Engine Controls - Theory & Operation - Cng, Flex-Fuel & Gasoline: Other Ford Explorer III

Supercharger By-Pass System

Supercharger By-Pass (SCB) system allows high pressure air at outlet of supercharger to vent back to inlet side of supercharger. This equalizes pressure and eliminates boost for times when supercharger function is not required. Descriptions of supercharger by-pass system components are as follows

1. Vacuum By-Pass Actuator During normal operation engine vacuum is applied to upper port of vacuum by-pass actuator. Lower port of vacuum by-pass actuator references air pressure in clean air tube, cancelling out any pressure difference in intake air system. Actuator opens during engine high vacuum conditions (by-passing supercharger). As throttle is opened and engine vacuum decreases, vacuum by-pass actuator closes to allow supercharger to pressurize air in intake manifold.
2. SCB Solenoid/Thermactor Air Control Solenoid SCB solenoid is used to control intake manifold vacuum to vacuum by-pass actuator. The SCB solenoid is de-energized during normal operating conditions. The Powertrain Control Module (PCM) will transmit an output signal to activate SCB solenoid to apply stored vacuum from vacuum reservoir assembly to vacuum by-pass actuator when an undesirable condition occurs in the engine. Once engine condition is corrected, SCB solenoid will be deactivated by PCM allowing engine intake manifold vacuum to control vacuum by-pass actuator.
3. Vacuum Reservoir Assembly Vacuum reservoir assembly stores vacuum that is applied to the vacuum actuator when a condition such as overheating or critical sensor failure is generated.

Supercharger Intercooler (Charge Air Cooler) System

Intercooler system is designed to cool induction air which has been heated by the supercharger. Removing heat from pressurized air through an intercooler increases air density, which results in increased combustion efficiency, engine horsepower and torque.

Intercooler system consists of the following components: an additional radiator and coolant reservoir (independent from engine cooling system), an intercooler (charge air cooler) located in lower intake manifold and a charge air cooler pump (electric water pump) located at right front side of engine compartment and intercooler coolant hoses. (Scheme 20)

Charge air cooler pump is controlled by PCM and charge air cooler pump relay to maintain a desirable intake air temperature signalled by a second intake air temperature sensor (IAT2) located in lower intake manifold.

Scheme 20

Intake Manifold Runner Control - Focus 2.0L (VIN P), Econoline & Pickup 4.2L (VIN 2) & Windstar 3.8L (VIN 4)

On 3.8L & 4.2L engines, Intake Manifold Runner Control (IMRC) system consists of a remote mounted electric actuator with an attaching cable or linkage to operate the housing butterfly valve plate levers located between intake manifold and cylinder head(s). (Scheme 21)- (Scheme 24). On 2.0L, IMRC uses a motorized actuator mounted directly to a single housing, between intake manifold and cylinder head, without use of a cable or linkage. PCM uses a positive change in Throttle Position (TP) sensor along with the increase in engine RPM from Crankshaft Position (CKP) sensor to open butterfly valve plates.

IMRC housing is an aluminum casting with 2 intake air passages for each cylinder. One passage is always open and the other is opened and closed with a butterfly valve plate(s). IMRC housing uses a return spring to hold butterfly valve plate(s) in closed position. Electric actuator houses an internal switch or switches, dependent on application, to provide feedback to PCM indicating butterfly valve plate(s) position.

When engine speed is less than 3000 RPM, electric actuator will not be energized, allowing IMRC butterfly valve plate(s) to remain in closed position. When engine speed is approximately 3000 RPM or more, electric actuator is energized, causing butterfly valve plate(s) to the open position to improve high speed engine performance. Some applications will activate IMRC butterfly valve plate(s) when engine speed is about 1500 RPM.

Scheme 21

Scheme 22

Scheme 23

Scheme 24

Intake Manifold Swirl Control Vacuum Actuated System - Ranger 2.3L (VIN D)

Intake Manifold Swirl Control (IMSC) vacuum actuated system consists of manifold mounted vacuum actuator and Powertrain Control Module (PCM) controlled electric solenoid. (Scheme 25)and (Scheme 26). PCM monitors Throttle Position (TP) sensor, cylinder head temperature sensor and crankshaft position sensor signals to determine activation of IMSC. A positive change in voltage from TP sensor along with increase in RPM at proper engine temperature must be present to open valve plates. When conditions are met to open valves, PCM energizes IMSC solenoid and vacuum is then applied to actuator to pull butterfly plates open.

Linkage from actuator attaches to manifold butterfly plate lever. IMSC actuator and manifold are a composite/plastic with a single intake air passage for each cylinder. The passage has a butterfly valve plate that blocks 60 percent of intake opening when actuated, leaving top of intake passage open to generate turbulence. A return spring is used to hold butterfly valve plates closed. Vacuum actuator provides feedback to PCM indicating butterfly valve plate position.

When engine speed is less than 3000 RPM, vacuum solenoid will be energized to allow manifold vacuum to be applied and butterfly valve plates will remain closed. When engine speed is 3000 RPM or more, vacuum solenoid is de-energized to allow vacuum to vent from actuator and butterfly valve plates will open.

Scheme 25

Scheme 26

Intake Manifold Tuning Valve - LS, Sable & Taurus 3.0L (VIN S), Econoline & Pickup 4.6L (VIN W), & Blackwood 5.4L 4VPC (VIN A)

Intake Manifold Tuning Valve (IMTV) is an electric actuator mounted directly to intake manifold. IMTV operates a shutter device attached to electric actuator shaft. When electric actuator is energized, it rotates shaft and opens shutter, allowing both sides of the manifold airflow to blend together. (Scheme 27)- (Scheme 30).

There is no monitor feedback to PCM from IMTV to indicate shutter position (open or closed). PCM uses a positive change in throttle position sensor along with the increase in engine RPM from crankshaft position sensor to open shutter.

When engine speed is below 2600 RPM, electric actuator will not be energized, allowing IMTV shutter to remain in closed position (no airflow blend occurs). When engine speed is 2600 RPM or more, electric actuator is initially energized at a 100 percent duty cycle, causing shutter to open position (airflow blend occurs). Duty cycle then falls to about 50 percent duty cycle to continue to hold shutter open.

Scheme 27

Scheme 28

Scheme 29

Scheme 30

POWERTRAIN CONTROL MODULE

Powertrain Control Module (PCM) monitors engine operating conditions by input received from engine sensors. PCM receives input from sensors and other electronic components, such as switches or relays. Based on information received and programmed into its memory, PCM generates output signals to control various components, such as relays, solenoids and actuators.

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES , which control or produce voltage signals monitored by PCM. The second category covers OUTPUT SIGNALS , covering components controlled by PCM.

There are 4 types of PCM used. A 150-pin PCM which has 3 separate electrical harness connectors (Aviator, Explorer, LS, Mountaineer and Thunderbird), a 150-pin PCM which has 3 separate electrical harness connectors (Focus 2.3L), a 122-pin PCM which has 3 separate electrical harness connectors (Expedition and Navigator) and a 104-pin PCM which has one electrical harness connector (all others). (Scheme 31)- (Scheme 34). For PCM location, see POWERTRAIN CONTROL MODULE LOCATION table.

PCM uses a memory integrated circuit chip which stores information for Keep Alive Random Access Memory (KAM). For additional KAM information, see KEEP ALIVE RANDOM ACCESS MEMORY under POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS. Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within PCM. This IC contains software code required by PCM to control powertrain. For additional EEPROM information, see FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY under POWERTRAIN CONTROL SOFTWARE.

In the event that one or more input sensors fail, PCM initiates an alternative operating procedure called Failure Mode Effects Management (FMEM) to allow the vehicle to maintain driveability. For additional information on FMEM, see FAILURE MODE EFFECTS MANAGEMENT under POWERTRAIN CONTROL SOFTWARE. If PCM detects an engine overheating condition, it activates a fail-safe cooling strategy. For additional information, see FAIL-SAFE COOLING STRATEGY under POWERTRAIN CONTROL SOFTWARE. In the event of PCM failure, Hardware Limited Operation Strategy (HLOS) will be activated. For additional information on HLOS, see HARDWARE LIMITED OPERATION STRATEGY under POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS.

POWERTRAIN CONTROL MODULE LOCATION

Scheme 31

Scheme 32

Scheme 33

Scheme 34

Integrated Electronic Ignition System

Integrated Electronic Ignition (EI) System consists of a Crankshaft Position (CKP) sensor, coil pack(s), connecting wiring, and PCM. Coil On Plug (COP) Integrated EI System uses a separate coil for each spark plug and each coil is mounted directly onto plug. COP Integrated EI System eliminates the need for spark plug wires but does require input from Camshaft Position (CMP) sensor. For additional EI system information, see INTEGRATED ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEMS.

Keep Alive Random Access Memory

Keep Alive Random Access Memory (KAM) stores memory of vehicle operating conditions and then uses this information for adaptive learning. KAM remains powered with ignition off so that input and output information is not lost.

Vehicle Buffered Power

Vehicle Buffered Power (VBPWR) is a PCM supplied power source that supplies regulated voltage (10-14 volts) to Vistronic Drive Fan (VDF) Fan Speed Sensor (FANSS) under normal operating conditions. It regulates to VPWR minus 1.5 volts, and voltage output is limited to protect sensor. For additional VDF clutch information, see VISTRONIC DRIVE FAN under OUTPUT SIGNALS.

Vehicle Power

When ignition switch is turned to START or RUN position, battery positive voltage (B+) is applied to coil of PCM power relay. Since other end of coil is wired to ground, this energizes coil and closes contacts of PCM power relay. Vehicle power (VPWR) is now sent to PCM and various OBD-II systems.

Vehicle Reference Voltage

Vehicle Reference Voltage (VREF) is a positive voltage (about 5 volts) that is output by PCM. This is a consistent voltage that is used by 3-wire sensors.

Mass Air Flow Return

Mass Air Flow Return (MAF RTN) is a dedicated analog signal return from Mass Air Flow (MAF) sensor. It serves as a ground offset for analog voltage differential input by MAF sensor to PCM.

Signal Return

Signal Return (SIG RTN) is a dedicated ground circuit used by most OBD-II sensors and some other inputs.

Power Ground

Power Ground (PWR GND) is an electric current path return for VPWR voltage circuit. The purpose of PWR GND is to maintain sufficient voltage at PCM.

Gold Plated Terminals

Note. Damaged gold terminals should only be replaced with NEW gold terminals.

Some engine control hardware has gold plated terminals on connectors and mating harness connectors to improve electrical stability for low current draw circuits and to enhance corrosion resistance. OBD-II components equipped with gold terminals will vary by vehicle application.

Engine RPM/Vehicle Speed Limiter

PCM will disable some or all fuel injectors whenever an engine RPM or vehicle overspeed condition is detected. This prevents damage to the powertrain. Excessive wheel slippage caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in RPM while in NEUTRAL or while driving may cause engine RPM/vehicle speed limiter to be enabled. When engine RPM/vehicle speed limiter has been enabled, vehicle will exhibit a rough running engine condition, and PCM will store DTC P1270. After driver reduces excessive speed, engine will return to normal operating mode. No repairs are required. Technician should clear DTC from PCM and inform customer of the reason for DTC. Excessive wheel slippage may be caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in RPM while in Neutral or while driving.

Fail-Safe Cooling Strategy

Fail-safe cooling strategy is activated by PCM only in the event that an overheating condition has been detected. This strategy provides engine temperature control when cylinder head temperature exceeds certain limits. Cylinder head temperature is measured by Cylinder Head Temperature (CHT) sensor. For additional CHT sensor information, see CYLINDER HEAD TEMPERATURE SENSOR under INPUT DEVICES.

Note. Not all vehicles equipped with a CHT sensor will have fail-safe cooling strategy.

A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Along with a CHT sensor, fail-safe cooling strategy is used to prevent damage by allowing air cooling of engine. This strategy allows the vehicle to be driven safely for a short time with some loss of performance when an overheating condition exists. Engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power.

Note. A Wide Open Throttle (WOT) delay is incorporated if CHT temperature is exceeded during WOT operation. At WOT, injectors will function for a limited amount of time allowing customer to complete a passing maneuver.

Before injectors are disabled, fail-safe cooling strategy alerts customer to a cooling system problem by moving instrument cluster temperature gauge to HOT zone and a PCM DTC P1285 is set. Depending on the vehicle, other indicators, such as an audible chime or warning lamp, can be used to alert customer of fail-safe cooling. If overheating continues, fail-safe cooling strategy begins to disable fuel injectors, a DTC P1299 is stored in PCM memory and a Malfunction Indicator Light (MIL), either CHECK ENGINE or SERVICE ENGINE SOON will illuminate. If overheating condition continues and a critical temperature is reached, all fuel injectors are turned off and engine is disabled.

Failure Mode Effects Management

Failure Mode Effects Management (FMEM) is an alternate system strategy in PCM designed to maintain engine operation if one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by PCM, an alternative strategy is initiated. PCM substitutes a fixed value and continues to monitor incorrect sensor input. If suspect sensor operates within limits, PCM returns to normal engine operational strategy. All FMEM sensors display a sequence error message on scan tool. Message may or may not be followed by Key On Engine Off (KOEO) or Continuous Memory DTCs when attempting Key On Engine Running (KOER) self-test mode.

Flash Electrically Erasable Programmable Read Only Memory

Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within PCM. This IC contains software code required by PCM to control powertrain. EEPROM can be electrically erased and then reprogrammed without removing PCM from vehicle. If a software change is required to PCM, PCM can be reprogrammed through Data Link Connector (DLC) using scan tool.

Fuel Trim

Short Term Fuel Trim. If the oxygen sensors are warmed up and the PCM determines that the engine can operate near stoichiometric air/fuel ratio (14.7 to 1 for gasoline), the PCM goes into closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy must constantly adjust the desired air/fuel ratio rich and lean to get the oxygen sensor to "switch" around the stoichiometric point. If the time between switches are the same, then the system is actually operating at stoichiometry. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometry is represented by 0 percent. Richer (more fuel) is represented by a positive number and leaner (less fuel) is represented by a negative number. Normal operating range for short term fuel trim is plus or minus 25 percent. Some calibrations will have time between switches and short term fuel trim excursions that are not equal. These unequal excursions are used to run the system slightly lean or rich of stoichiometry. This practice is referred to as using "bias". For example, the fuel system can be biased slightly rich during closed loop fuel to help reduce NOx.

Values for SHRTFT1 and 2 may change a great deal on a scan tool when the engine is operated at different RPM and load points. This is because SHRTFT1 and 2 will react to fuel delivery variability that can change as a function of engine RPM and load. Short term fuel trim values are not retained after the engine is turned off.

Long Term Fuel Trim. While the engine is operating in closed loop fuel, the short term fuel trim corrections can be "learned" by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in Keep Alive Memory (KAM) in tables that are referenced by engine speed and load (and by bank for engines with two HO2S sensors forward of the catalyst). Learning the corrections in KAM improves both open loop and closed loop air/fuel ratio control. Advantages include

1. Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop.
2. Long term fuel trim corrections can be used both while in open loop and closed loop modes.

Long term fuel trim is represented as a percentage, just like short term fuel trim, however it is not a single parameter. There is a separate long term fuel trim value that is used for each RPM/load point of engine operation. Long term fuel trim corrections may change depending on the operating conditions of the engine (RPM and load), ambient air temperature and fuel quality (percent alcohol, oxygenates, etc.). When viewing the LONGFT1/2 PID(s), the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1/2 PID(s) will display the long term fuel trim correction that is currently being used at that RPM/load point.

As fuel control and air metering components age and vary from nominal values, fuel trim learns corrections while in closed loop fuel control. Corrections are stored in a table that is a function of engine speed and load. Tables reside in Keep Alive Random Access Memory (RAM) and are used to correct fuel delivery during open and closed loop. As changing conditions continue, individual cells are allowed to update for that speed load point. If both Short Term FT and Long Term FT reach their high or low limit and can no longer compensate during adaptive process, MIL is illuminated and a DTC is stored. Whenever a fuel injector or fuel pressure regulator is replaced, RAM should be cleared. This is necessary so PCM does not use previously learned fuel trim values. To clear RAM, see KEEP ALIVE RANDOM ACCESS MEMORY RESET PROCEDURE under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article.

Idle Air Trim

Idle Air Trim is designed to adjust Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. Idle air trim values are stored in a table for reference. This table is used by PCM as a correction factor when controlling idle speed. The table is stored in Keep Alive Random Access Memory (RAM) and retains the learned values even after engine is shut off. A DTC is output if idle air trim has reached its learning limits.

Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that RAM be cleared. This is necessary so idle strategy does not use previously learned idle air trim values. To clear RAM, see KEEP ALIVE RANDOM ACCESS MEMORY RESET PROCEDURE under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article. It is important to note that erasing DTCs with a scan tool does not reset idle air trim table. Once RAM has been reset, engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as strategy adapts. Adaptation occurs in 4 separate modes. The modes are shown in IDLE AIR TRIM LEARNING MODES table.

IDLE AIR TRIM LEARNING MODES

Idle Speed Control Closed Throttle Determination

One of the fundamental criteria for entering RPM control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position voltage seen since engine start. This lowest learned value is called "ratch", since the software acts like a one-way ratch. The ratch value (voltage) is displayed as TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest steady TP voltage seen after engine starts. In some cases, ratch can learn higher values of TP. The time to learn higher values is significantly longer than the time to learn lower values. The brakes must also be applied to learn the higher values.

All PCM functions are done using this ratch voltage, including idle speed control. PCM goes into closed throttle mode when TP voltage is at ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volt, will put PCM in part throttle mode. Throttle mode can be viewed by looking at TP MODE PID. With throttle closed, PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle RPM control, and could result in a high idle. Ratch can be corrupted by a Throttle Position (TP) sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.

Multiplexing

The increased number of modules on the vehicle necessitates a more efficient method of communication. Multiplexing is a method of designating a system for sending two or more signals simultaneously over a single circuit. In an automotive application, multiplexing is used to allow two or more electronic modules to communicate simultaneously over a single media. Typically this media is a twisted pair of wires. The information or messages that can be communicated on these wires consists of commands, status or data. The advantage of using multiplexing is to reduce the weight of the vehicle by reducing the number of redundant components and electrical wiring.

Multiplexing Implementation

Currently Ford Motor Company uses two different types of communication language protocols to communicate with the Powertrain Control Module (PCM). These protocols are Standard Corporate Protocol (SCP) and Controller Area Network (CAN). Starting with the 2003 model year, Ford will phase-in High Speed-CAN (HS-CAN) for PCM communication with the following vehicles

1. LS
2. Thunderbird
3. Focus 2.3L Partial Zero Emission Vehicle (PZEV)

The LS and Thunderbird will use HS-CAN between the Data Communication Link (DCL) connector and the PCM for scan tool to PCM diagnostics only. Inter communication (PCM to other network modules) for the LS and Thunderbird will continue to use SCP. The Focus 2.3L PZEV will use HS-CAN for PCM and instrument cluster (IC) module communication and for scan tool diagnostics.

All other vehicles for model year 2003 will continue to use SCP as its communication media for the PCM.

Standard Corporate Protocol

SCP is a communication language protocol based on SAE J1850 and is used by Ford Motor Company for exchanging bi-directional message (signals) between electronic modules. Two or more signals can be sent over one SCP network circuit. Fords SCP network operates at 41.6 kB/sec.

Included in these messages is diagnostic data that is outputted over the BUS (+) and BUS (-) lines to the Data Link Connector (DLC). PCM connection to the DLC is typically done with a two wire, twisted pair cable used for network interconnection. The diagnostic data such as Self-Test or PIDs can be accessed with a scan tool.

High Speed - Controller Area Network (HS-CAN)

HS-CAN is based on SAE J2284, ISO-11898 and is a serial communication language protocol used to transfer messages (signals) between electronic modules or nodes. Two or more signals can be sent over one CAN network circuit allowing two or more electronic modules or nodes to communicate with each other. This communication or multiplexing network operates at 500 kB/sec and allows the electronic modules to share their information messages.

Included in these messages is diagnostic data that is outputted over the CAN High (+) and CAN Low (-) lines to the Data Link Connector (DLC). PCM connection to the DLC is typically done with a two wire, twisted pair cable used for the network interconnection. The diagnostic data such as Self-test or PIDs can be accessed with a scan tool.

CONSTANT CONTROL RELAY MODULE

Constant Control Relay Module (CCRM) provides vehicle power to powertrain control module and electronic system. CCRM controls cooling fan and A/C clutch. CCRM also contains Fuel Pump Driver Module (FPDM) power supply relay, which supplies power to FPDM. If any of the internal components of CCRM fail, entire unit must be replaced. For location of CCRM, see CONSTANT CONTROL RELAY MODULE LOCATION table.

CONSTANT CONTROL RELAY MODULE LOCATION

FUEL PUMP DRIVER MODULE

Note. On LS and Thunderbird, Fuel Pump Driver Module (FPDM) functions are incorporated into Rear Electronic Module (REM). Fuel pump operation is same as applications using the stand-alone FPDM. REM will communicate diagnostic information through BUS (+) and BUS (-) circuits instead of using a fuel pump monitor circuit.

FPDM receives a duty-cycle signal from PCM and controls fuel pump operation in relation to this duty cycle. This results in variable fuel pump operation speed. The FPDM sends diagnostic information to PCM on fuel pump monitor circuit.

GENERIC ELECTRONIC MODULE

Automatic 4-Wheel Drive (A4WD) system is a full time 4-wheel drive system with an electronic shift 4x4 system that allows the operator to choose between three different 4x4 modes. The operator can switch between A4WD, and 4WD high mode at any speed, and 4WD low mode. In A4WD mode, Generic Electronic Module (GEM) varies torque split between front and rear driveline by controlling transfer case clutch. Transfer case clutch allows for slight speed differences between front and rear driveshaft which normally occurs when negotiating a corner on dry pavement. When rear wheels are overpowered, GEM detects this slip condition, and duty cycle to transfer case clutch is increased until speed difference between driveshafts is reduced.

NATURAL GAS VEHICLE MODULE

Note. F150 5.4L bi-fuel model uses an Alternative Fuel Control Module (AFCM) to allow communication between PCM and AFCM. AFCM is incorporated within compuvalve on F150 bi-fuel models. For additional information on bi-fuel system, see appropriate THEORY & OPERATION - BI-FUEL article.

Natural Gas Vehicle (NGV) module has 2 functions. The first function is to operate fuel injectors and is referred to as Injector Driver Module (IDM). The second function sends a fuel level indicator signal to drive the fuel gauge and is called Fuel Indicator Module (FIM). IDM vehicle fuel indicator driver signals are based on PCM fuel injector driver signals and are controlled directly by corresponding injector drivers in PCM. IDM must be used to provide NG fuel injectors with the required high current necessary for proper operation. The greater demand of fuel injector current warrants an increased size of injector driver and increased heat dissipation. Given these conditions, PCM would not be suitable for location of these drivers. IDM closely resembles 60-pin EEC-IV PCM module in appearance. See NATURAL GAS VEHICLE MODULE LOCATION table.

IDM injector drivers are capable of controlling amount of current flow to each NG fuel injector. Once fuel injector is open, IDM NG fuel injector driver will reduce current flow to a sufficient amount to continue to hold fuel injector open in an effort to reduce heat. If IDM driver does not detect required peak current to initially open NG fuel injector within a specified amount of time, IDM driver will drop current to fuel injector hold open current. The FIM is not part of the powertrain control subsystem.

NATURAL GAS VEHICLE MODULE LOCATION

INPUT DEVICES

Note. Transmission related PCM inputs are not listed here. For a complete listing of transmission related PCM inputs, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device used on a specific model, see WIRING DIAGRAMS . The available input devices include the following

A/C Cycling Switch

Note. Some applications do not have a dedicated (separate) input to PCM indicating that A/C is requested. This information is received by PCM through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits.

The A/C Cycling Switch (ACCS) may be wired to either the ACCS or ACPSW PCM input. When the A/C cycling switch opens, the PCM will turn off the A/C clutch.

The ACCS circuit to the PCM provides a voltage signal which indicates when the A/C is requested. When the A/C demand switch is turned on, and both the A/C cycling switch and the high pressure contacts of the A/C high pressure switch (if equipped and in circuit) are closed, voltage is supplied to the ACCS circuit at the PCM. See WIRING DIAGRAMS .

If the ACCS signal is not received by the PCM, the PCM circuit will not allow the A/C to operate. For additional information, see WIDE OPEN THROTTLE A/C CUT-OFF RELAY under PCM OUTPUTS.

Some applications do not have a dedicated (separate) input to the PCM indicating that A/C is requested. This information is received by the PCM through the BUS + and BUS - (SCP) communication.

Air Conditioning Evaporator Temperature Sensor

Air Conditioning Evaporative Temperature (ACET) sensor senses evaporator air discharge temperature. ACET sensor is a thermistor device in which resistance changes with temperature. Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. PCM sources a low current 5 volts on ACET circuit. With SIG RTN also connected to ACET sensor, varying resistance affects voltage drop across sensor terminals. As A/C evaporator air temperature changes, varying resistance of ACET sensor changes voltage PCM detects. ACET sensor is used to more accurately control A/C clutch cycling, improving defrost/demist performance, and reduce A/C clutch cycling.

Air Conditioning Pressure Sensor

Air Conditioning Pressure (A/C pressure) sensor is located in high pressure (discharge) side of A/C system. A/C pressure sensor provides a voltage signal to PCM that is proportional to A/C pressure. (Scheme 35) PCM uses this information for A/C clutch control, fan control and idle speed control.

Scheme 35

A/C High Pressure Switch

The A/C high pressure switch is used for additional A/C system pressure control. A/C high pressure switch is either dual function for 2-speed fan control applications or single function for all other applications. For refrigerant containment control, the normally closed high pressure contacts open at a predetermined A/C pressure. This will result in A/C turning off, preventing A/C pressure from rising to a level that would open A/C high pressure relief valve. For fan control, the normally open medium pressure contacts close at a predetermined A/C pressure. This grounds the ACPSW circuit input to Powertrain Control Module (PCM). The PCM will then turn on the high speed fan to help reduce A/C pressure.

Brake Pedal Position Switch

The Brake Pedal Position (BPP) switch is used by the PCM to disengage the transmission torque converter clutch and on some applications as an input to the idle speed control for idle quality and for vehicle speed control deactivation. Depending on the vehicle application the BPP switch can be connected to the PCM in the following manner

1. BPP switch is hard wired to the PCM supplying battery positive voltage (B+) when the vehicle brake is applied.
2. BPP switch is hard wired to a module (ABS, LCM or REM), BPP signal is than broadcasted over the data link to be received by the PCM.
3. BPP switch is hard wired to the anti-lock brake (ABS)- traction control/stability assist module. The stability module will interpret the BPP switch input along with other ABS inputs and generate an output called the Driver Brake Application (DBA) signal. The DBA signal is than sent to the PCM and to other BPP signal users.

On applications where the BPP switch is hard wired to the PCM and stoplamp circuit, if all stoplamp bulbs are burned out (open), high voltage is present at the PCM due to a pull-up resistor in the PCM. This provides fail-safe operation in the event the circuit to the stoplamp bulbs has failed.

Brake Pressure Applied/Brake Deactivator Switch

Brake Pressure Applied (BPA) switch is sometimes called Brake Deactivator switch for vehicle speed control deactivation, is a normally closed switch, which supplies battery positive voltage (B+) to PCM when brake pedal is not applied. When brake pedal is applied, the normally closed switch will open and power is removed from PCM. On some applications the normally closed BPA switch along with the normally open Brake Pedal Position (BPP) switch are used for a brake rationality test within PCM. PCM misfire monitor profile learn function can be disable if a brake switch failure occurs. If one or both brake pedal inputs to PCM did not change states when they were expected to, DTC P1572 may be set by PCM.

Camshaft Position Sensor

A 3-pin Hall Effect type Camshaft Position (CMP) sensor or a 2-pin variable reluctance sensor is used. (Scheme 36)and (Scheme 37). CMP sensor is used to determine camshaft position and to identify when piston No. 1 is on its compression stroke. CMP sensor signal is used by PCM for synchronizing the firing of sequential fuel injectors. Applications with Coil On Plug (COP) ignition also use CMP signal to select the proper ignition coil to fire. The input circuit to PCM is referred to as the CMP input or circuit.

Scheme 36

Scheme 37

Clutch Pedal Position Switch

Clutch Pedal Position (CPP) switch is mounted near clutch pedal. CPP switch is an input for Powertrain Control Module (PCM) indicating clutch pedal position and, in some manual transmission applications, both clutch pedal position and gearshift position. PCM provides a 5-volt reference (VREF) signal to CPP and/or Park/Neutral Position (PNP) switch (on CPP signal circuit). If CPP switch is closed (indicating clutch pedal applied) and shift lever is in Neutral position, output voltage from PCM is grounded through signal return circuit to PCM and one volt or less will be present. If CPP switch (or PNP switch, or both CPP and PNP switches) is open, meaning clutch pedal is released (all systems), or shift lever is not in Neutral position (PNP switch systems), CPP input signal to PCM will be about 5 volts, indicating a load on engine. PCM uses load information for mass airflow and fuel calculations.

Crankshaft Position Sensor

Crankshaft Position (CKP) sensor is a magnetic transducer mounted on engine block, next to crankshaft pulse wheel. On all engines except 6.8L, trigger wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. On 6.8L, trigger wheel has a total of 39 teeth spaced 9 degrees apart and one 9 degree empty space for a missing tooth. By monitoring pulse wheel, CKP sensor indicates crankshaft position and speed information to PCM. By monitoring missing tooth, CKP sensor is also able to identify piston travel to synchronize ignition system and provide a way of tracking angular position of crankshaft relative to a fixed reference.

Cylinder Head Temperature Sensor

Cylinder Head Temperature (CHT) sensor is mounted in an aluminum cylinder head and measures metal temperature. CHT sensor is a thermistor which changes resistance proportionate to temperature changes. Resistance increases as cylinder head temperature decreases and decreases as cylinder head temperature increases. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus the voltage drop across the fixed resistor. If CHT sensor signal indicates an overheating condition, PCM will initiate a fail-safe cooling strategy based on information from CHT sensor. For additional information, see FAIL-SAFE COOLING STRATEGY under POWERTRAIN CONTROL SOFTWARE. Using both CHT sensor and fail-safe cooling, PCM prevents damage by allowing air cooling of engine and limp home capability.

Differential Pressure Feedback EGR Sensor

See DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM under EGR SYSTEMS.

Engine Coolant Temperature Sensor

Engine Coolant Temperature (ECT) sensor is a thermistor device in which resistance changes with temperature. Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to temperature. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in a series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor. ECT measures temperature of engine coolant and is threaded into an engine coolant passage. ECT sensor is similar in construction to IAT sensor.

Engine Fuel Temperature Sensor

Engine Fuel Temperature (EFT) sensor inputs fuel temperature of fuel near fuel injectors to the PCM. EFT sensor is a thermistor device which changes resistance proportionate to temperature changes. Resistance increases as fuel temperature decreases and decreases as fuel temperature increases. Signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.

Engine Oil Temperature Sensor

The Engine Oil Temperature (EOT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The EOT sensor measures the temperature of the engine oil. The sensor is typically threaded into the engine oil lubrication system near the oil filter. The PCM can use the EOT sensor input to determine the following

1. On Variable Cam Timing (VCT) applications the EOT input is used to adjust the VCT control gains and logic for camshaft timing.
2. The PCM can use EOT sensor input in conjunction with other PCM inputs to determine oil degradation.
3. The PCM can use EOT sensor input to initiate a soft engine shutdown. To prevent engine damage from occurring as a result of high oil temperatures, the PCM has the ability to initiate a soft engine shutdown. Whenever engine RPM exceeds a calibrated level for a certain period of time, the PCM will begin reducing power by disabling engine cylinders.

Fan Speed Sensor

See VISTRONIC DRIVE FAN under OUTPUT SIGNALS.

Fuel Level Input

Fuel Level Input (FLI) is a hard wire signal input to PCM from Fuel Pump (FP) module. See description of FLI under ENHANCED EVAPORATIVE EMISSION SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Fuel Pump Monitor (With Fuel Pump Driver Module)

Fuel Pump Driver Module (FPDM) communicates diagnostic information to PCM through Fuel Pump Monitor (FPM) circuit. This information is sent by FPDM as a duty cycle signal. The 3 duty cycle signals that may be sent are listed in FUEL PUMP DRIVER MODULE DUTY CYCLE SIGNALS table. PCM uses this signal to verify FPDM is powered and able to communicate on the FPM circuit.

FUEL PUMP DRIVER MODULE DUTY CYCLE SIGNALS

Fuel Pump Monitor (Without Fuel Pump Driver Module)

The Fuel Pump Monitor (FPM) circuit is spliced into Fuel Pump Power (FP PWR) circuit and is used by PCM for diagnostic purposes. PCM sources a low current voltage down FPM circuit. With fuel pump off, voltage is pulled low by path to ground through fuel pump. With fuel pump off and FPM circuit low, PCM can verify FPM and FP PWR circuits are complete from FPM splice through fuel pump to ground. This also confirms that FP PWR or FPM circuits are not shorted to power.

With fuel pump on, voltage is supplied from fuel pump relay to FP PWR and FPM circuits. With fuel pump on and FPM circuit high, PCM can verify FP PWR circuit from fuel pump relay to FPM splice is complete. It can also verify that fuel pump relay contacts are closed and battery voltage is supplied to fuel pump relay.

Fuel Tank Pressure Sensor

See ENHANCED EVAPORATIVE EMISSION SYSTEM under FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Fuel Rail Pressure Sensor

On Crown Victoria 4.6L NGV, Fuel Rail Pressure (FRP) sensor is a diaphragm strain gauge device in which resistance changes with pressure. (Scheme 38) Electrical resistance of a strain gauge increases as pressure increases, and decreases as pressure decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to pressure. Strain gauge type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor.

Scheme 38

On all others, FRP sensor measures pressure of fuel near fuel injectors. (Scheme 39) This signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder. FRP sensor senses pressure difference between fuel rail and intake manifold. Return fuel line to fuel tank has been deleted in this type of fuel system. Differential of fuel/intake manifold pressure together with measured fuel temperature provides an indication of fuel vapors in fuel rail. Both differential pressure and temperature feedback signals are used to control fuel pump speed. Fuel pump speed sustains fuel rail pressure which preserves fuel in its liquid state. Dynamic range of fuel injectors increases because of higher rail pressure, which allows injector pulse width to decrease.

Scheme 39

Generator Load

The Generator Load Input (GLI) circuit is used by the PCM to determine generator load on the engine. As generator load increases the PCM will adjust idle speed accordingly. This strategy helps reduce idle surges due to switching high current loads. The GLI signal is sent to the PCM from the voltage regulator/generator. The signal is a variable frequency duty cycle. Normal operating frequency is 40-250 Hz. Normal signal DC voltage (referenced to ground) is between 1.5 V (low generator load) and 10.5 V (high generator load). See GENERATOR LOAD INPUT under PCM CONTROLLED CHARGING SYSTEM under MISCELLANEOUS CONTROLS.

Generator Monitor

See GENERATOR MONITOR under PCM CONTROLLED CHARGING SYSTEM under MISCELLANEOUS CONTROLS.

Heated Oxygen Sensor

Heated Oxygen Sensors (HO2S) are mounted in or right after exhaust manifold before catalytic converter (upstream HO2S), and in exhaust pipe after catalytic converter (downstream HO2S). HO2S detects presence of oxygen in exhaust gases and produces a variable voltage according to amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in exhaust gases produces a low voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a high voltage signal more than 0.6 volt. HO2S provides feedback to PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. HO2S generates a voltage between 0.0 and 1.1 volts.

Embedded with the sensing element is the HO2S heater. The heating element heats sensor to 1400°F (800°C). At approximately 600°F (300°C), engine can enter closed loop operation. VPWR circuit supplies voltage to heater and PCM will complete the ground when the proper conditions occur. Starting in 1998, a new HO2S heater and heater control system are installed on some vehicles. The high power heater reaches closed loop fuel control temperatures. Use of this heater requires HO2S heater control be duty cycled, to prevent damage to heater. The 6-ohm design is not interchangeable with new style 3.3-ohm heater.

Intake Air Temperature Sensor

Intake Air Temperature (IAT) sensors and integrated MAF type, are thermistor devices in which resistance changes with temperature. (Scheme 40)and (Scheme 41). Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to temperature. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow.

Scheme 40

Voltage that is dropped across a fixed resistor in a series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor. IAT provides air temperature information to PCM. PCM uses air temperature information as a correction factor in calculation of fuel, spark and MAF. IAT sensor provides a quicker temperature change response time than ECT or CHT sensor.

Supercharged vehicles use 2 IAT sensors. Both sensors are thermistors. However, one is located before the supercharger at air cleaner for standard OBD-II cold weather input, while the second sensor (IAT2) is located after the supercharger in intake manifold. IAT2 sensor located after supercharger provides air temperature information to PCM to control border-line spark and to help determine intercooler (charge air cooler) efficiency.

Currently 2 types of IAT2 sensors are used on supercharged vehicles. A screw in type and an integrated type, which is part of Thermal Manifold Absolute Pressure (TMAP) sensor. (Scheme 40)and (Scheme 42). TMAP sensor consists of an IAT thermistor and a Manifold Absolute Pressure (MAP) sensor. The thermistor portion of TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the TMAP, see THERMAL MANIFOLD ABSOLUTE PRESSURE SENSOR.

Intake Manifold Runner Control

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Intake Manifold Swirl Control

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Intake Manifold Tuning Valve

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Knock Sensor

The Knock Sensor (KS) is a tuned accelerometer located on the engine, which converts engine vibration to an electrical signal. PCM uses this signal to determine the presence of engine knock and retards spark timing accordingly.

Mass Airflow Sensor

Mass Airflow (MAF) sensor is located between air cleaner and throttle body, or inside air cleaner assembly. MAF sensors use a hot wire sensing element to measure amount of air entering the engine. Air passing over the hot wire causes it to cool. The hot wire is maintained at 392°F (200°C) greater than ambient temperature, as measured by a constant cold wire. (Scheme 41)

The current required to maintain hot wire operating temperature is proportional to the intake air mass flow. MAF sensor outputs an analog voltage signal to PCM proportional to intake air mass. PCM uses this signal to calculate fuel injector pulse width in order to provide the desired air/fuel ratio. On some applications, MAF sensor input is used in determining transmission Electronic Pressure Control (EPC), shift and Torque Converter Clutch (TCC) scheduling.

Most MAF sensors have Integrated By-Pass Technology (IBT) with an integrated Intake Air Temperature (IAT) sensor.

Scheme 41

Output Shaft Speed Sensor

Output Shaft Speed (OSS) sensor provides PCM with information about rotational speed of transmission output shaft. PCM uses information to control and diagnose powertrain behavior. In some applications, OSS sensor is also used as source of monitoring vehicle speed. OSS sensor may be physically located in different places on vehicle, depending upon the specific application. Design of each OSS sensor is unique and depends on which powertrain control feature uses the information generated.

Power Steering Pressure Sensor

Power Steering Pressure (PSP) sensor monitors power steering pressure. PSP sensor voltage input to PCM will change as hydraulic pressure changes. PCM uses PSP sensor input signal to compensate for additional loads on engine by adjusting idle speed RPM, and prevents engine stall during parking maneuvers. PCM also uses PSP signal to adjust transaxle/transmission Electronic Pressure Control (EPC) pressure during increased engine load.

Power Steering Pressure Switch

Power Steering Pressure (PSP) switch monitors power steering pressure. PSP switch is normally closed and opens as pressure increases. PCM uses PSP switch input signal to compensate for additional loads on engine by adjusting idle speed RPM, and prevents engine stall during parking maneuvers. PCM also uses PSP signal to adjust transaxle/transmission Electronic Pressure Control (EPC) pressure during increased engine load.

Power Take-Off Switch

Power Take-Off (PTO) circuit is used by PCM to disable some OBD-II monitors during PTO operation. PTO switch is normally open and circuit voltage is normally low. When PTO switch is closed, battery voltage is supplied to PTO circuit, indicating an additional load condition to PCM. If an additional load condition is not reported to PCM by PTO circuit, a false DTC may be stored.

Thermal Manifold Absolute Pressure Sensor

The Thermal Manifold Absolute Pressure (TMAP) sensor consists of a Manifold Absolute Pressure (MAP) sensor and an integrated thermistor. The MAP portion of the sensor uses a piezo-resistive silicon sensing element to provide a voltage proportional to the absolute pressure in the intake manifold. The thermistor portion of the sensor operates in the same manner as an Intake Air Temperature (IAT) sensor. For additional information on how the IAT sensor operates, see INTAKE AIR TEMPERATURE SENSOR .

For the Ranger 2.3L and Focus 2.3L PZEV, the TMAP sensor is part of the Exhaust Gas Recirculation (EGR) system. The PCM uses information from the MAP portion of the TMAP sensor, Throttle Position (TP) sensor, Mass Air Flow (MAF) sensor, Engine Coolant Temperature (ECT) sensor or Cylinder Head Temperature (CHT) sensor and Crankshaft Position (CKP) sensor to determine how much exhaust gas is introduced into the intake manifold. The thermistor portion of the TMAP sensor is currently not being used on this application.

For the Mustang 4.6L SC, the PCM uses manifold absolute pressure information from the MAP portion of the TMAP sensor along with other sensor inputs to determine the proper amount of fuel needed for combustion under varying engine load conditions. The thermistor portion of the TMAP sensor is used as a second IAT sensor. This second IAT sensor, located after the supercharger, provides manifold air temperature information to the PCM.

Scheme 42

Throttle Position Sensor

Throttle Position (TP) sensor is a rotary potentiometer sensor that provides a signal to PCM that is linearly proportional to throttle plate/shaft position. TP sensor housing has a 3-blade electrical connector that may be gold plated. The gold plating increases corrosion resistance on terminals and increases connector durability. TP sensor is mounted on throttle body and has 4 operating conditions: closed throttle (idle or deceleration), part throttle (cruise or moderate acceleration), wide open throttle (includes maximum acceleration or de-choke on crank), and throttle angle rate. TP sensor signal affects air/fuel ratio, injector timing, idle speed, EGR flow and ignition timing.

Transmission Control Switch

Transmission Control Switch (TCS) may also be referred to as overdrive (O/D) cancel switch. The TCS signals the PCM with keypower whenever the TCS is pressed. TCS position is controlled by vehicle operator. If overdrive is disengaged, O/D OFF indicator located on instrument panel, or Transmission Control Indicator Light (TCIL) located on shift lever, will illuminate.

Vehicle Speed Sensor

Vehicle Speed Sensor (VSS) is a variable reluctance or Hall Effect type sensor that generates a waveform with a frequency that is proportional to vehicle speed. When vehicle is moving slowly, sensor produces a low frequency signal. As vehicle speed increases, sensor produces a higher frequency signal. PCM uses this signal to control fuel injection, ignition timing and transaxle/transmission shift and Torque Converter Clutch (TCC) scheduling.

4x4 Mode Switch

Generic Electronic Module (GEM) provides PCM with an indication of 4x4L. This input is used to adjust transmission shift scheduling. A 5-volt module pull-up indicates 4x4H or 2WD. (Scheme 43)

Scheme 43

OUTPUT DEVICES

Note. Transmission related PCM outputs are not listed here. For a complete listing of transmission related PCM inputs, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

Vehicles are equipped with different combinations of computer controlled components. Not all components listed are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

Canister Vent Solenoid

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Coil Pack

A coil in a coil pack is turned on (coil charging) by PCM, and is turned off when 2 spark plugs are fired simultaneously. Spark plugs are paired so that one spark plug fires on the compression stroke and other spark plug fires on exhaust stroke. Next time coil is fired, order is reversed and next pair of spark plugs fire according to engine firing order.

Coil On Plug

Coil On Plug (COP) ignition operates similar to a standard coil pack ignition except each spark plug has one coil per spark plug. (Scheme 44) COP has 3 different modes of operation

1. Engine Cranking During engine cranking, PCM will fire 2 spark plugs simultaneously. One spark plug will fire on compression stroke and the other spark plug fires on exhaust stroke. Both spark plugs will fire until camshaft position is identified by a successful camshaft sensor signal.
2. Engine Running Once camshaft position is identified and engine is running, only spark plug with cylinder under compression will be fired.
3. CMP Failure Mode Effects Management (CMP FMEM) During CMP FMEM, COP ignition operates similar to engine cranking mode. This allows engine to operate without requiring PCM to know if cylinder is on compression or exhaust stroke.

Scheme 44

Electric EGR Motor System

For information on the Electric Exhaust Gas Recirculation (EEGR) system, see ELECTRIC EGR MOTOR SYSTEM under EGR SYSTEMS.

EGR System Module

For information on the EGR System Module (ESM), see EGR SYSTEM MODULE under EGR SYSTEMS.

EGR Vacuum Regulator Solenoid

See EGR SYSTEMS .

Electric Secondary Air Injection Pump

See ELECTRIC SECONDARY AIR INJECTION SYSTEM under SECONDARY AIR INJECTION SYSTEM.

Evaporative Emission Canister Purge Valve

Note. Evaporative Emission Canister Purge (CANP) Valve may also be referred to as Vapor Management Valve (VMV).

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Fan Control

The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C on/off status, A/C pressure, etc.) to determine engine cooling fan needs.

For Variable Speed Electric Fan(s): The PCM controls the fan speed and operation using a duty cycle output on the Fan Control - Variable (FCV) circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor). (Scheme 45)

Scheme 45

For Relay Controlled Fans: The PCM controls the fan operation through the Fan Control (FC) (single speed fan applications), Low Fan Control (LFC), Medium Fan Control (MFC) and/or High Fan Control (HFC) outputs. For three speed fans, although the PCM output circuits are called low, medium and high fan control (FC), cooling fan speed is controlled by a combination of these outputs. (Scheme 46)

Scheme 46

Fuel Cap Off Indicator Light

Note. Escape, Expedition, LS, Mustang, Navigator, Thunderbird, Town Car and Windstar do not have a dedicated output wire from PCM to instrument cluster. PCM commands Fuel Cap Off Indicator Light (FCIL) on and off through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits.

FCIL is an output signal controlled by PCM and will illuminate when it is determined there is a failure in vapor management system due to fuel filler cap not being sealed properly. This would be detected by inability to pull vacuum in fuel tank, after a fueling event.

Fuel Injectors

See FUEL INJECTORS under FUEL CONTROL under FUEL SYSTEMS (GASOLINE), or NG FUEL INJECTORS under FUEL CONTROL under FUEL SYSTEMS (NATURAL GAS).

Generator Communication

See GENERATOR COMMUNICATION under PCM CONTROLLED CHARGING SYSTEM under MISCELLANEOUS CONTROLS.

Idle Air Control Valve

See IDLE AIR CONTROL VALVE ASSEMBLY under IDLE CONTROL SYSTEM under AIR INDUCTION SYSTEMS.

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

See VARIABLE INDUCTION SYSTEM under AIR INDUCTION SYSTEMS.

Malfunction Indicator Light

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

Secondary Air Injection By-Pass Solenoid

See ELECTRIC SECONDARY AIR INJECTION SYSTEM under SECONDARY AIR INJECTION SYSTEM.

Solid State Relay

See ELECTRIC SECONDARY AIR INJECTION SYSTEM under SECONDARY AIR INJECTION SYSTEM.

Thermostat Heater Control

The primary objective for the thermostat heater control is for improvement in fuel economy and thermal efficiency. The system consists of a high temperature 208°F (98°C) instead of a 194°F (90°C) thermostat that has a resistive heater within a wax element. (Scheme 47) The heater is controlled by PCM dependent on engine speed, throttle position, engine load, vehicle speed, air charge temperature, transmission oil temperature and engine coolant temperature. During low speed, low load and low air charge temperature conditions, the thermostat heater is OFF and engine is allowed to operate at an elevated coolant temperature. This should result in lower internal friction and higher thermal efficiency, both leading to improved fuel economy.

Scheme 47

During high speed, high load, high temperature conditions (air charge, transmission oil or engine coolant), PCM output is energized with a duty cycle to thermostat heater. This heats the wax and forces thermostat to rapidly open wider allowing extra coolant to flow from radiator. This will reduce coolant temperature and improve with performance demand. The heater is only capable of supplying a small amount of additional heat to wax element. It is not capable of opening thermostat alone. The thermostat is 100 percent duty cycle for short calibrated time and than duty cycle is reduced to a maximum of 70 percent ON and 30 percent OFF. Unheated, thermostat will begin to open at a coolant temperature of about 208°F (98°C), and will be fully open at 226°F (108°C). Energizing heater will reduce opening temperature to about 154°F (68°C), and the fully open temperature to 217°F (103°C).

Transmission Control Indicator Light

Transmission Control Indicator Light (TCIL) is an output signal from PCM that controls indicator light on/off function depending on engagement or disengagement of overdrive. See TRANSMISSION CONTROL SWITCH under INPUT DEVICES.

Wide Open Throttle A/C Cut-Off Relay

Note. The Wide Open Throttle A/C Cut-Off (WAC) relay may also be referred to as the A/C clutch relay.

The WAC relay is normally open (normally closed for Aviator). There is no direct electrical connection between A/C switch or Electronic Air Temperature Control (EATC) module and A/C clutch. On some applications, A/C request signal will be sent to PCM through Standard Corporate Protocol (SCP) BUS (+) and BUS (-) circuits. When A/C is requested, PCM will ensure all other A/C related inputs and engine components are operating correctly before grounding WAC relay output (unground for Aviator), causing voltage to be sent to A/C clutch.

Vapor Management Valve

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS.

Vehicle Speed Output

Powertrain Control Module - Vehicle Speed Output (PCM-VSO) speed signal subsystem generates vehicle speed information for vehicle's electrical/electronic modules and subsystems that require vehicle speed data. This subsystem senses transmission output shaft speed using a sensor. See OUTPUT SHAFT SPEED SENSOR or VEHICLE SPEED SENSOR under INPUT DEVICES. Vehicle speed data is processed by PCM and distributed as a hard-wired signal or as a multiplexed data message.

Key features of PCM-VSO system are to

1. Infer Vehicle Movement From Output Shaft Sensor Signal
2. Convert Transmission Output Shaft Rotational Information To Vehicle Speed Information
3. Compensate For Tire Size & Axle Ratio With A Programmed Calibration Variable
4. Utilize Transfer Case Sensor For Four Wheel Drive Applications
5. Distribute Vehicle Speed Information As A Multiplexed Message &/Or An Analog Signal

The signal from a non-contact shaft sensor mounted on transmission (OSS) or transfer case (TCSS) is sensed directly by PCM. PCM converts OSS or TCSS information to 8000 pulses per mile, based on a tire and axle ratio conversion factor. This conversion factor is programmed into PCM at time of vehicle assembly and can be reprogrammed in the field for servicing changes in tire size and axle ratio. PCM transmits computed vehicle speed and distance traveled information to all vehicle speed signal users.

VSO information can be transmitted by a hard-wired interface between vehicle speed signal user and PCM, or by speed and odometer Standard Corporate Protocol (SCP) multiplexed data messages. VSO hard-wired signal wave form is a DC square wave with a voltage level of zero to battery voltage. Typical output operating range is 2.22Hz per MPH. Multiplexed data for speed and distance data are transmitted as separate SCP messages over SCP multiplex link.

Vistronic Drive Fan

The primary purpose for the Vistronic Drive Fan (VDF) clutch is to optimize fan energy (i.e. improved fuel economy) while meeting cooling performance requirements. Successful optimization will also minimize objectionable fan noise. The operation is similar to the existing viscous fan clutch, except viscous fluid flow is controlled by a Pulse Width Modulated (PWM) solenoid versus a bi-metal temperature sensor on the front of the clutch.

The VDF consists of three main elements, a working chamber, a reservoir chamber, and a Fan Speed Sensor (FANSS). A fluid port valve controls fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, "shearing" of the fan clutch fluid will result in fan rotation. The valve is activated via a PWM output signal from the PCM. By opening and closing the fluid port valve, the PCM can control approximate fan speed. Fan speed is monitored via a Hall Effect sensor and is read by the PCM for closed loop operation.

The PCM will optimize the VDF fan speed based upon CHT, TFT, or IAT cooling requirements. When either of these inputs is demanding increased fan speed for vehicle cooling, the PCM will monitor the Hall Effect Fan Speed Sensor (FANSS), and output the resultant PWM signal to the fluid port valve thus controlling to the required fan speed.

FUEL DELIVERY

FUEL SYSTEM IDENTIFICATION

There are 3 different types of fuel systems that are used

Returnable Fuel System

Returnable fuel system consists of a fuel tank with a reservoir, fuel pump module, fuel supply lines, fuel filter(s), Schrader/pressure test port, fuel rail, fuel injectors, and fuel pressure regulator. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 48)

1. The fuel delivery system uses Crankshaft Position (CKP) sensor to signal PCM that engine is either cranking or running.
2. The fuel pump logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground fuel pump relay for one second during Key On Engine Off. During cranking, fuel pump relay is grounded as long as PCM receives a CKP signal.
3. The fuel pump relay has a primary and a secondary circuit. Primary side is controlled by PCM and secondary side provides battery voltage (B+) to fuel pump circuit when relay is energized.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(ref-153170-S34610515122003032100000).
5. The fuel injector is a solenoid operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see «FUEL INJECTORS»(ref-153170-S25132090352003032100000) under FUEL CONTROL.
6. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
7. The fuel pressure regulator, also referred to as the pulse damper, is mounted to the fuel pump bracket within the fuel tank. It regulates fuel pressure supplied to fuel injectors. (Scheme 49)
8. There are 4 filtering or screening devices in fuel delivery system. Fuel intake sock or screen is a fine, nylon mesh mounted on intake side of fuel pump. (Scheme 50) There is a fuel filter screen located at fuel rail side of fuel injector. A fuel filter/screen is located in the inlet side of fuel pressure regulator. The fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
9. The Fuel Pump (FP) module is a device that contains both fuel pump and fuel sender assembly. The fuel pump is located inside reservoir and supplies fuel through fuel pump module manifold to engine and fuel pump module jet pump. (Scheme 51)

Scheme 48

Scheme 49

Scheme 50

Scheme 51

Mechanical Returnless Fuel System

Note. Fuel rail pulse damper used on mechanical returnless fuel systems should not be confused with a fuel pressure regulator. Both are visually similar, but the fuel rail pulse damper does not regulate fuel pressure. Damper is used to reduce fuel system noise. Vacuum port on fuel rail pulse damper is connected to manifold vacuum to avoid fuel spillage if damper diaphragm ruptures.

Electronic returnless fuel system consists of a fuel tank with reservoir, fuel pump, fuel pressure regulator, fuel filter, fuel supply line, fuel rail, fuel rail pulse damper, fuel injectors, and Schrader/pressure test port. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 52)

1. The fuel delivery system is enabled during crank or running mode once PCM receives a Crankshaft Position (CKP) sensor signal.
2. The fuel pump logic is defined in the fuel system control strategy and is executed by PCM.
3. The PCM grounds fuel pump relay, which provides Vehicle Power (VPWR) to fuel pump.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(ref-153170-S34610515122003032100000).
5. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
6. The fuel rail pulse damper is located on fuel rail to reduce fuel system noise caused by pulsing of fuel injectors. The vacuum port located on damper is connected to manifold vacuum to avoid fuel spillage in the event pulse damper diaphragm were to rupture. Pulse damper should not be confused with a fuel pressure regulator.
7. The fuel injector is a solenoid-operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see «FUEL INJECTORS»(ref-153170-S25132090352003032100000) under FUEL CONTROL.
8. There are 3 filtering or screening devices in fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on intake side of fuel pump. (Scheme 53) There is a fuel filter screen located at fuel rail side of fuel injector, and the fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
9. The Fuel Pump (FP) module contains fuel pump, fuel pressure regulator and fuel sender assembly. The fuel pump has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Fuel pressure regulator is attached to fuel pump in fuel pump module located in fuel tank. It regulates fuel pressure supplied to fuel injectors. The fuel pressure regulator is a diaphragm operated relief valve, wherein fuel pressure is established by a spring preload applied to diaphragm. Excess fuel is by-passed through regulator and returned to fuel tank.

Scheme 52

Scheme 53

Electronic Returnless Fuel System

Electronic returnless fuel system consists of a fuel tank with reservoir, fuel pump, fuel rail pressure sensor, fuel filter, fuel supply line, engine fuel temperature sensor, fuel rail, fuel injectors, and Schrader/pressure test point. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 54)

1. The fuel delivery system is enabled during crank or running mode once PCM receives a Crankshaft Position (CKP) sensor signal.
2. The fuel pump logic is defined in fuel system control strategy and is executed by PCM.
3. The PCM commands a duty cycle to Fuel Pump Driver Module (FPDM).
4. The FPDM modulates voltage to Fuel Pump (FP) to achieve proper fuel pressure. Voltage for fuel pump is supplied by power relay or FPDM power supply relay. For additional FPDM information, see «FUEL PUMP DRIVER MODULE»(ref-153170-S37465800692003032100000) under COMPUTERIZED ENGINE CONTROLS.
5. The Fuel Rail Pressure (FRP) sensor provides PCM with current fuel rail pressure. PCM uses this information to vary duty cycle output to FPDM to compensate for varying loads.
6. The Engine Fuel Temperature (EFT) sensor measures current fuel temperatures in fuel rail. This information is used to vary fuel pressure and avoid fuel system vaporization.
7. The fuel injector is a solenoid-operated valve that meters fuel flow to each cylinder. Fuel injector is opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector information, see «FUEL INJECTORS»(ref-153170-S25132090352003032100000) under FUEL CONTROL.
8. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.
9. There are 3 filtering or screening devices in fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on intake side of fuel pump. (Scheme 55) There is a fuel filter screen located at fuel rail side of fuel injector, and the fuel filter assembly is located between fuel pump and pressure test point/Schrader valve.
10. The Fuel Pump (FP) module is a device that contains fuel pump and fuel sender assembly. The fuel pump has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Fuel pump is located inside reservoir and supplies fuel through fuel pump module manifold to engine and fuel pump module jet pump. The reservoir prevents fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels.
11. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(ref-153170-S34610515122003032100000).

Scheme 54

Scheme 55

Inertia Fuel Shutoff Switch (All Fuel Systems)

In the event of a collision or vehicle rollover, electrical contacts within the Inertia Fuel Shutoff (IFS) switch are tripped open when the internal steel ball breaks loose of the switch magnet. (Scheme 56) Once loose, the steel ball rolls up a conical ramp and makes contact with the target plate which creates an open in the electrical circuit to electric fuel pump. If the electrical circuit is opened, it is not possible to restart the vehicle until the switch is reset. A reset button is located on top of IFS switch assembly.

Scheme 56

FUEL CONTROL

Note. Fuel injectors are deposit resistant and must not be cleaned.

The fuel injector is a solenoid-operated valve that meters fuel flow to the engine. (Scheme 57) The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open.

The fuel injector is normally closed and is operated by 12 volt VPWR from the electronic engine control power relay. The ground signal is controlled by the PCM.

The injector is the Deposit Resistant Injection (DRI) type and does not have to be cleaned. However, it can be flow checked and, if found outside of specification, the fuel injector should be replaced.

Scheme 57

Natural Gas (NG) fuel system consists of fuel tank(s), fuel shutoff valve assemblies, fuel supply lines, fuel filter, manual shutoff valve(s), service (Schrader) valve, fuel injection supply manifold and fuel pressure regulator. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 58)

1. The Crankshaft Position (CKP) sensor is used to signal PCM that engine is either cranking or running.
2. The fuel shutoff valve logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground fuel pump relay for one second during Key On Engine Off (KOEO). During cranking, fuel pump relay is grounded as long as PCM receives a signal from CKP.
3. The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by PCM and secondary side provides battery voltage (B+) to fuel shutoff valve circuit when relay is energized.
4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision). For additional IFS information, see «INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS)»(ref-153170-S34610515122003032100000).
5. The fuel injector is used to meter natural gas to each combustion cylinder. Although NG fuel injector appears very similar to some gasoline fuel injectors, it is unique. Flow capacity of this fuel injector is 6-12 times as large as various gasoline fuel injectors. (Scheme 59) For additional NG fuel injector information, see «NG FUEL INJECTORS»(ref-153170-S20734823852003032100000) under FUEL CONTROL.
6. The fuel tank shutoff solenoid valve is located in fuel tank. The solenoid valves are on the same circuit as fuel pump and utilize the same Inertia Fuel Shutoff (IFS) switch as gasoline models. For additional fuel tank shutoff solenoid valve information, see «FUEL TANK SHUTOFF VALVE»(ref-153170-S19038710982003032100000).
7. The high pressure fuel filter is used to protect engine fuel system components. A natural gas coalescing and particulate filter is located on high pressure side of fuel system just prior to fuel pressure regulator. Filter is part of regulator assembly. Filter can be disassembled to service the element. Drain plug on bottom of filter housing can be removed to drain any accumulated water.
8. Fuel pressure regulator used on NG vehicles is a single-staged pressure reducing regulator which expands natural gas from storage pressures of 200-3000 psi (1379-20,685 kPa) to engine fuel pressures of 105-125 psi (724-862 kPa). For additional NG fuel pressure regulator information, see «NG FUEL PRESSURE REGULATOR»(ref-153170-S38866954552003032100000).
9. The fuel rail shutoff valve is a normally closed solenoid actuated valve that opens when terminal No. 80 is grounded by PCM. The valve isolates fuel injectors from fuel line pressure when engine is not operating. The fuel rail shutoff valve is wired in parallel with fuel tank shutoff solenoid valves. For additional fuel rail shutoff valve information, see «FUEL RAIL SHUTOFF VALVE»(ref-153170-S27284644592003032100000).

Scheme 58

Scheme 59

Fueling Connector

The flange assembly is designed for 3000 psi (20,685 kPa) service pressure and is the refueling connection to fill vehicle. The assembly is mounted behind fuel filler door and attached to fuel filler housing, similar to a gasoline vehicle. This assembly consists of an NGVP1 type receptacle with a 150-micron filter (which can be serviced), a spring loaded check valve to allow filling of vehicle and a manually opened bypass to provide safe venting of fuel system. The vehicle is refueled by attaching fuel station fill nozzle to receptacle and locking into place.

Fuel Lines & Fittings

A fuel line assembly consists of flexible hose and/or stainless steel seamless tubing, end fittings and tube nuts. The hose is a conductive polytetrafluoroethylene (PTFE) liner reinforced with a stainless steel wire braided covering. The fittings are inserted into hose ends and crimped into place. The stainless steel tubing contains end fittings which are brazed to the tube. There are high pressure fuel lines that are identified by either 1/4-inch or 3/8-inch outer diameter, and a low pressure fuel line identified by a 1/2-inch outer diameter. The low pressure fuel line has a quick-connect at one end for connection to fuel rail. The other fittings used on natural gas vehicle to connect fuel components are SAE "O" ring face seal tube fittings. There are 2 end types: an "O" ring face seal end and a straight thread end. On tee and elbow fittings, a washer and a positionable nut are provided to aid in orientation of the fitting.

Fuel Rail

The fuel rail distributes low pressure fuel from chassis supply line to each fuel injector. Fuel pressure at top of each fuel injector is maintained within 1 percent of other fuel injectors at all times, done by nearly symmetric flow paths. The fuel rail is also designed to have minimal flow restriction by increasing cross-sectional flow area and reducing flow path length. The fuel rail contains several other components that perform crucial functions. (Scheme 59) These include

1. Injection Pressure Sensor Measures the pressure of fuel near fuel injectors. This signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.
2. Engine Fuel Temperature Sensor Measures pressure of fuel near fuel injectors. This signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.
3. Low Pressure Solenoid Shutoff Valve Isolates fuel rail from upstream fuel system when engine is OFF. This minimizes the amount of fuel available to flow through fuel injectors when engine is off or leak from a damaged fuel rail during and after a crash. The valve is controlled by PCM fuel shutoff valve circuit and contains an inertia switch. The valve is only on for one second after a key-on or whenever CKP signals are being received by PCM.
4. Schrader/Service Valve Provides a service port to low pressure fuel system. This valve is needed to relieve pressure in system before and during service. This valve could also be used to monitor pressure near injectors during diagnostic procedures.

Fuel Rail Shutoff Valve

The fuel rail shutoff valve is a normally closed valve that opens when terminal No. 80 is grounded by PCM. (Scheme 60) Resistance of the fuel rail shutoff valve coil is 11 ohms. When ignition switch is in ON position, power relay is turned on. Power relay provides power to PCM and control side of fuel shutoff valve relay. Relay provides voltage to fuel rail valve. If ignition switch is not in START position, PCM will close fuel rail shutoff valve after one second. PCM will open valve, along with the tank valve(s), to provide fuel while cranking. The valve will remain open when engine is running unless IFS switch is "tripped".

Scheme 60

Fuel Tank Shutoff Valve

The fuel tank shutoff valve is located in fuel tank(s). (Scheme 61) When ignition switch is in OFF position, fuel tank shutoff valves are closed and fuel in the tanks is isolated. During refueling, fuel tank shutoff valve acts as a check valve and allows flow due to pressure differential between fuel being added from fill station and fuel in the tank.

The fuel tank shutoff valve internal solenoid valves also have capability of being manually locked down. While servicing vehicle, if it becomes necessary to remove the fuel tank, lock down feature provides an added measure of safety.

The fuel tank shutoff valve has an internal Canadian Gas Association (CGA) type 9 fusible link pressure relief device that senses internal fuel tank gas temperature. Fuel tank is vented to the atmosphere when internal fuel tank gas temperature reaches 217°F (199°C) and melts fusible link. The escaping gas is vented through a vent line.

Scheme 61

Inertia Fuel Shutoff Switch

See INERTIA FUEL SHUTOFF SWITCH (ALL FUEL SYSTEMS) under FUEL SYSTEMS (GASOLINE).

NG Fuel Pressure Regulator

The fuel pressure regulator used in the Natural Gas fuel system is a single-stage pressure reducing regulator which expands natural gas from storage pressures of 200-3000 psi (1379-20,685 kPa) to engine fuel injector pressures of 105-125 psi (724-862 kPa).

The regulator contains a pressure relief device, a 275 psi (1896 kPa) check valve, which protects the low pressure fuel system. The low pressure fuel system no longer must fulfill the design requirements of the high pressure fuel system, therefore reducing cost, weight and complexity.

When gas expands, the fuel temperature drops significantly causing extreme cold temperatures (-160°F or -177°C) that may damage synthetic fuel system components as well as cause water vapor within the fuel to condense, freeze and plug the lines, valve and injectors. To prevent this, engine coolant is routed through the fuel pressure regulator to warm the fuel before it expands.

The regulator has an internal thermostat to control the flow of engine coolant. This prevents overheating and subsequent thinning of the fuel which may cause lean combustion. Outlet coolant flow is restricted by the thermostat when it rises above approximately 100°F (82°C).

See NATURAL GAS VEHICLE MODULE under COMPUTERIZED ENGINE CONTROLS.

NG Fuel Injectors

The fuel injector is a solenoid-operated valve that meters fuel flow to the engine. The fuel injector is opened and closed every other crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open.

The fuel injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.

The fuel injectors are used to meter natural gas to each combustion cylinder. Although the natural gas fuel injectors appear very similar to some gasoline fuel injectors, they are unique. Flow capacity of these fuel injectors is 6 to 12 times as large as various gasoline fuel injectors. Electrical resistance is much lower than typical gasoline fuel injectors (4.6 ohms as opposed to 14.5 ohms). To accommodate this lower resistance, a fuel injector driver module is used to convert the PCM fuel injector driver signal to the signal required by the fuel injector.

Note. Ignition timing is controlled by the Powertrain Control Module (PCM) and is not adjustable. DO NOT attempt to check base timing as false readings will result.

Coil Pack System

The EI system consists of a CKP sensor, coil pack(s), related wiring and PCM. The CKP sensor is used by PCM to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted on front of crankshaft. The coil pack receives the signal from the PCM to fire at a calculated spark target. Each coil within the pack fires 2 spark plugs at the same time.

The plugs are paired so one plug is fired on the compression stroke, and the other plug fires the mating cylinder, which is on the exhaust stroke. On the next cycle, firing is reversed. On 6-tower coil pack applications the matched cylinder pairs are: No. 1 and 5, No. 2 and 6, and No. 3 and 4. (Scheme 62)and (Scheme 63).

On single 4-tower coil pack applications (4-cylinder), the matched cylinder pairs are No. 1 and 4, and No. 2 and 3. (Scheme 64)and (Scheme 65). On dual 4-tower coil pack applications (8-cylinder), the matched cylinder pairs are No. 1 and 6, No. 3 and 5, No. 4 and 7, and No. 2 and 8. (Scheme 65)

The PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, positive battery voltage applied to the coil primary circuit builds a magnetic field around the primary coil. When the switch opens, power is interrupted and the primary field collapses inducing high voltage in the secondary coil winding and the spark plug is fired.

Scheme 62

Scheme 63

Scheme 64

Scheme 65

Coil On Plug System

Individual COPs are mounted directly on spark plugs. (Scheme 44) CKP sensor is used by PCM to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted on front of crankshaft. The CMP sensor is used by PCM to identify when piston No. 1 is at Top Dead Center (TDC) of compression stroke. This signal is used to synchronize firing of individual coils.

The individual coils receive their signal from PCM to fire at a calculated spark target. Only one coil is fired at a time and only on compression stroke. PCM acts as an electronic switch to ground individual coil primary circuit. When the switch is closed, battery voltage applied to coil primary circuit builds a magnetic field around primary coil. When the switch opens, power is interrupted and primary field collapses, inducing high voltage in secondary coil winding and spark plug is fired. For additional COP information, see COIL ON PLUG under OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS.

Variable Cam Timing Solenoid Valve

The VCT solenoid valve is an integral part of the VCT system. (Scheme 66) The solenoid valve controls the flow of engine oil in the VCT assembly. As the PCM controls the duty cycle of the solenoid valve, oil pressure/flow advances or retards the cam timing. Duty cycles near 0 or 100 percent represent rapid movement of the camshaft. Retaining a fixed camshaft position is accomplished by dithering (oscillating) the solenoid valve duty near 50 percent.

Scheme 66

CATALYST SYSTEM

The catalytic converter and exhaust systems work together to control the release of harmful engine exhaust emissions into the atmosphere. Engine exhaust gas consists mainly of Nitrogen (N), Carbon Dioxide (CO2) and water vapor (H2O). However, it also contains Carbon Monoxide (CO), Oxides of Nitrogen (NOX), Hydrogen (H), and various unburned Hydrocarbons (HCs). CO, NOX, and HCs are major air pollutants, and their emission into the atmosphere must be controlled. The exhaust system generally consists of an exhaust manifold, front exhaust pipe, upstream Heated Oxygen Sensor (HO2S), rear exhaust pipe, downstream HO2S, a muffler and an exhaust tailpipe. The catalytic converter is installed between front and rear exhaust pipes. Catalytic converter efficiency is monitored by the OBD-II system. For additional OBD-II Monitor information, see DIAGNOSTIC MONITORS under COMPUTERIZED ENGINE CONTROLS.

The number of HO2S(s) used in the exhaust stream and the location of these sensors depend on the vehicle emission certification level (i.e. LEV, ULEV, PZEV). (Scheme 67)and (Scheme 68). On most vehicles, only two HO2S are used in an exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst will be used for primary fuel control while the ones after the catalyst (HO2S12/HO2S22) will be utilized to monitor catalyst efficiency. However, some Partial Zero Emission Vehicles (PZEV) will utilize three HO2S sensors for each engine bank. The stream 1 sensors (HO2S11/HO2S21) before the catalyst will be used for primary fuel control, the next group of sensors or stream 2 (HO2S12/HO2S22) is utilized to monitor the light-off catalyst and the last group of sensors or stream 3 (HO2S13/HO2S23) is utilized for long term fuel trim control to optimize catalyst efficiency (Fore Aft Oxygen Sensor Control). Currently Ford's PZEV vehicles use only a 4-cylinder engine, so only the Bank 1 HO2S(s) will be utilized. (Scheme 67)and (Scheme 68).

Scheme 67

Scheme 68

Catalytic Converter

A catalyst is a material that remains unchanged when it initiates and increases the speed of a chemical reaction. A catalyst will also enable a chemical reaction to occur at a lower temperature. The catalytic converter assists in controlling the concentration of exhaust gas products released to the atmosphere. It contains a catalyst in the form of a specially treated ceramic honeycomb structure saturated with catalytically active precious metals. As exhaust gases come in contact with the catalyst, they are changed into mostly harmless products. The catalyst initiates and speeds up heat producing chemical reactions of the exhaust gas components so they are used up as much as possible. For additional 3-Way Catalytic (TWC) converter information, see 3-WAY CATALYTIC CONVERTER .

Light Off Catalyst

As the catalyst heats up, converter efficiency rises rapidly. The point at which conversion efficiency exceeds 50 percent is called catalyst light off. For most catalysts this point occurs at 475-575°F (246-301°C). A fast light catalyst is a 3-Way Catalyst (TWC), that is located as close to exhaust manifold as possible. Because light off catalyst is located close to exhaust manifold it will light off faster and reduce emissions quicker than the catalyst located under vehicle. Once catalyst lights off, the catalyst will quickly reach maximum conversion efficiency.

3-Way Catalytic Converter

The 3-way Catalytic (TWC) converter contains either Platinum (Pt) and Rhodium (Rh), or Palladium (Pd) and Rhodium (Rh). TWC converter catalyzes oxidation reactions of unburned HCs and CO and reduction reaction of NOx. The 3-way conversion can be best accomplished by always operating engine air fuel/ratio at or close to stoichiometry (14.7:1). For additional stoichiometry information, see 3-WAY CATALYST CONVERSION EFFICIENCY .

3-Way Catalyst Conversion Efficiency

A TWC requires a stoichiometric fuel ratio, 14.7 pounds of air to one pound of fuel (14.7:1), for high conversion efficiency. In order to achieve these high efficiencies, air/fuel ratio must be tightly controlled with a narrow window of stoichiometry. Deviations outside of this window will greatly decrease conversion efficiency. (Scheme 69) For example, a RICH mixture will decrease HC and CO conversion efficiency, while a LEAN mixture will decrease NOx conversion efficiency.

Scheme 69

EXHAUST SYSTEM

The purpose of the exhaust system is to convey engine emissions from exhaust manifold to atmosphere. Engine exhaust emissions are directed from engine exhaust manifold to catalytic converter through front exhaust pipe. A Heated Oxygen Sensor (HO2S) is mounted on the front exhaust pipe before catalyst. Catalytic converter reduces concentration of Carbon Monoxide (CO), unburned Hydrocarbons (HCs) and Oxides of Nitrogen (NOx) in exhaust emissions to an acceptable level. Reduced exhaust emissions are directed from catalytic converter to a muffler through rear exhaust pipe. Another HO2S is mounted on rear exhaust pipe. Exhaust emissions are then directed to atmosphere through an exhaust tailpipe.

Hardware

The downstream HO2S may be located after light off catalyst or underbody catalyst. Underbody catalyst may be in-line with light off catalyst, or underbody catalyst may be common to 2 light off catalysts, forming a "Y" pipe configuration.

Exhaust Manifold & Runners

Exhaust manifold runners collect exhaust gases from engine cylinders. The number of exhaust manifolds and exhaust manifold runners depends on engine configuration and number of cylinders.

Exhaust Pipes

Exhaust pipes are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the product. The pipes serve as guides for flow of exhaust gases from engine exhaust manifold through catalytic converter and muffler.

Upstream & Downstream Heated Oxygen Sensors

Heated Oxygen Sensors (HO2S) provide PCM with voltage and frequency information related to oxygen content of exhaust gas. For additional HO2S information, see HEATED OXYGEN SENSOR under PCM INPUTS under COMPUTERIZED ENGINE CONTROLS.

Muffler

Mufflers are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the product. The muffler reduces noise levels produced by engine, and it also reduces noise produced by exhaust gases as they travel from catalytic converter to atmosphere.

FUEL EVAPORATIVE SYSTEMS

The Evaporative Emission (EVAP) system prevents fuel vapor build-up in the fuel tank. Fuel vapor trapped in fuel tank is vented through the vapor valve assembly on top of fuel tank. Fuel vapors leave the valve assembly through a single vapor line and continue on to the EVAP canister for storage until vapors are purged into the engine for burning. EVAP canister is located in engine compartment, in rear of vehicle near luggage compartment or underneath vehicle along the frame rail. There are 2 different types of EVAP systems that may be used

1. «ENHANCED EVAPORATIVE EMISSION SYSTEM»(ref-153170-S27206142222003032100000)
2. «ON-BOARD REFUELING VAPOR RECOVERY EVAP SYSTEM»(ref-153170-S15932377342003032100000)

ENHANCED EVAPORATIVE EMISSION SYSTEM

The enhanced Evaporative Emission (EVAP) system consists of a fuel tank, fuel filler cap, fuel tank mounted or in-line fuel vapor control valve, fuel vapor vent valve, EVAP canister, fuel tank mounted or fuel pump mounted or in-line Fuel Tank Pressure (FTP) sensor, EVAP canister purge valve, intake manifold hose assembly, Canister Vent (CV) solenoid, PCM and connecting wires and fuel vapor hoses. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 70)

1. Enhanced EVAP system uses inputs from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Mass Airflow (MAF) sensor, Vehicle Speed Sensor (VSS) and Fuel Tank Pressure (FTP) sensor to provide information about engine operating conditions to PCM. The Fuel Level Input (FLI) and FTP sensor signals are used by PCM to determine activation of EVAP Monitor based on presence of fuel vapor or fuel sloshing.
2. PCM calculates a variable duty cycle based on desired amount of purge vapor flow to intake manifold for a given engine condition. PCM can then output the duty cycle to solenoid on EVAP canister purge valve. PCM uses Enhanced EVAP system inputs to evacuate system, using EVAP canister purge valve, CV solenoid to seal Enhanced EVAP system from atmosphere, and uses FTP sensor to observe total vacuum lost for a period of time.
3. Canister Vent (CV) solenoid seals EVAP canister from atmospheric pressure. (Scheme 71) This allows EVAP canister purge valve to obtain fuel tank target vacuum during EVAP Leak Check Monitor.
4. PCM outputs a variable duty cycle signal (between zero and 100 percent) to solenoid on EVAP canister purge valve. For additional EVAP canister purge valve information, see «EVAP CANISTER PURGE VALVE»(ref-153170-S21484964192003032100000).
5. Fuel Tank Pressure (FTP) sensor monitors the fuel tank pressure during engine operation and continuously transmits an input signal to the PCM. During the EVAP monitor testing, the FTP sensor monitors the fuel tank pressure or vacuum bleed-up. (Scheme 72)and (Scheme 73).
6. The fuel tank mounted fuel vapor vent valve assembly, fuel tank mounted fuel vapor control valve (or remote fuel vapor control valve) are used in Enhanced EVAP system to control flow of fuel vapor entering engine. All of these valves also prevent fuel tank overfilling during refueling operation and prevent liquid fuel from entering EVAP canister and EVAP canister purge valve under any vehicle altitude, handling or rollover condition. The liquid/vapor fuel discriminator is part of fuel vapor control valve assembly on Focus and ZX2 models.

The Enhanced EVAP system, including all fuel vapor hoses, can be checked when a leak is detected by PCM. This can be done by pressurizing system using Rotunda Evaporative Emission Tester Kit (134-00056) or equivalent, and leak (frequency) detector included with kit.

Scheme 70

Scheme 71

Scheme 72

Scheme 73

EVAP Canister Purge Valve

EVAP canister purge valve is part of Enhanced EVAP system that is controlled by PCM. (Scheme 74)and (Scheme 75). This valve controls flow of vapors (purging) from EVAP canister to intake manifold during various engine operating modes. EVAP canister purge valve is a normally closed valve. The electronic EVAP canister purge valve controls the flow of vapors electronically by way of a solenoid thereby, eliminating the need for an electronic vacuum regulator and vacuum diaphragm. (Scheme 76)

Scheme 74

Scheme 75

Scheme 76

Fuel Filler Cap

The fuel filler cap is used to prevent fuel spill and close the evaporative emission/fuel system to atmosphere. Some vehicles may have a Fuel Cap Off Indicator Lamp (FCIL) in the instrument cluster which will illuminate when there is a failure in the vapor management system that may be due to the fuel filler cap not being sealed.

ON-BOARD REFUELING VAPOR RECOVERY EVAP SYSTEM

The basic elements forming the ORVR system operation are as follows when fuel is dispensed: (Scheme 77)and (Scheme 78).

1. The fuel filler pipe forms a seal to prevent vapors from escaping the fuel tank, while liquid is entering the fuel tank (liquid in the one inch diameter tube blocks vapors from rushing back up the fuel filler pipe).
2. A fuel vapor control valve controls the flow of vapors out of the fuel tank (valve closes when liquid level reaches a height associated with the fuel tank usable capacity). This valve accomplishes the following: Limits the total amount of fuel that can be dispensed into the fuel tank. Prevents liquid gasoline from exiting the fuel tank when submerged (and also when tipped well beyond a horizontal plane as part of the vehicle roll-over protection in road accidents). Minimizes vapor flow resistance during anticipated refueling conditions.
3. Fuel vapor tubing connects the fuel vapor control valve to the EVAP canister. This routes the fuel tank vapors (displaced by the incoming liquid) to the EVAP canister.
4. A check valve in the bottom of the fuel filler pipe prevents liquid from rushing back up the fuel filler pipe during the liquid flow variations associated with the filler nozzle shut-off.

Between refueling events, the EVAP canister is purged with fresh air so that it may be used again to store vapors accumulated during engine soaks or subsequent refueling events. The vapors drawn off of the carbon in the EVAP canister are consumed in the engine.

Scheme 77

Scheme 78

POSITIVE CRANKCASE VENTILATION

The Positive Crankcase Ventilation (PCV) system cycles crankcase gases back through the engine where they are burned. The PCV valve regulates the amount of ventilating air and blow-by gas to the intake manifold and prevents backfire from traveling into the crankcase. The PCV valve is designed with a quarter-turn cam-lock thread at one end to prevent accidental disconnection from the valve cover.

ELECTRIC SECONDARY AIR INJECTION SYSTEM

Electric Secondary Air Injection (AIR) system consists of an Electric AIR Pump (EAP), single or dual combination check air injection diverter (AIR diverter) valve(s), an AIR by-pass solenoid, a solid state relay, PCM, wiring and vacuum hoses. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 79)

1. PCM requires Engine Coolant Temperature (ECT), Intake Air Temperature (IAT) and Crankshaft Position (CKP) inputs to initiate secondary air injection function.
2. When engine is started, strategy will determine when to enable Electric Air Pump (EAP). After a 5-10 second delay, PCM signals solid state relay and AIR by-pass solenoid to begin system operation. Once catalyst is lit-off, PCM then signals solid state relay to stop EAP operation and to close AIR by-pass solenoid from supplying vacuum to AIR diverter valve(s). For additional AIR by-pass solenoid or AIR diverter valve information, see «AIR BY-PASS SOLENOID»(ref-153170-S32413616402003032100000) or «AIR DIVERTER VALVE»(ref-153170-S21070538162003032100000).
3. Solid state relay provides start-up signal and will switch high current required to operate EAP. Input control to solid state relay comes from PCM. (Scheme 80)
4. AIR by-pass solenoid applies a vacuum to AIR diverter valve(s) causing it to open and to allow air to flow into exhaust manifolds.
5. Vacuum check valve controls vacuum bleed-off to solenoid.
6. Function of splash cap, if equipped, is to provide EAP with a source of dry air.
7. EAP delivers required amount of air to control emissions during engine operation. Air is forced into exhaust manifolds to oxidize hydrocarbons and carbon monoxide created by running rich at start up. For additional EAP information, see «ELECTRIC AIR PUMP»(ref-153170-S30373678242003032100000).

Scheme 79

Scheme 80

Scheme 81

AIR By-Pass Solenoid

Secondary AIR by-pass solenoid is used by PCM to control vacuum to secondary AIR diverter valve. AIR by-pass solenoid is a normally closed solenoid. AIR by-pass solenoid also has a filtered vent feature to permit vacuum release. (Scheme 81)

AIR Diverter Valve

The secondary air injection diverter (AIR diverter) valve is used with Electric Air Pump (EAP) to provide on/off control of air to exhaust manifold and catalytic converter. (Scheme 81) When EAP is on and vacuum is supplied to AIR diverter valve, air passes integral check valve disk. When EAP is off, and vacuum is removed from AIR diverter valve, integral check valve disk is held on the seat and stops air from being drawn into exhaust system and prevents backflow of exhaust into secondary air injection system.

Electric AIR Pump

Electric AIR Pump (EAP) provides pressurized air to secondary air injection system. EAP functions independently of RPM and is controlled by PCM. EAP is used for short periods of time. Delivery of air is dependent on amount of system backpressure and system voltage. Inlet system of EAP incorporates a non-serviceable filter and splash cap which helps to guard against dirt and water. (Scheme 81)

EGR SYSTEMS

Note. The self-diagnostic system monitors EGR system performance and sets a Diagnostic Trouble Code (DTC) if self-test requirements are not obtained.

DIFFERENTIAL PRESSURE FEEDBACK EGR SYSTEM

Differential Pressure Feedback (DPFE) EGR system consists of a DPFE EGR sensor, EGR vacuum regulator solenoid, EGR valve, orifice tube assembly and Powertrain Control Module (PCM). The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 82)

1. DPFE EGR system receives signals from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor and Crankshaft Position (CKP) sensor to provide information on engine operating conditions to PCM. Engine must be warm, stable and running at a moderate load and engine speed (RPM) before EGR system is activated. PCM deactivates EGR during idle, extended Wide Open Throttle (WOT), or whenever a failure is detected in an EGR component or EGR required input.
2. PCM calculates desired amount of EGR flow for a given engine condition. It then determines desired pressure drop across metering orifice required to achieve that flow and outputs corresponding signal to EGR vacuum regulator solenoid.
3. EGR vacuum regulator solenoid receives a variable duty cycle signal between 0-100 percent. The higher the duty cycle, the more vacuum the solenoid diverts to EGR valve. For additional EGR vacuum regulator solenoid information, see «EGR VACUUM REGULATOR SOLENOID»(ref-153170-S05306383872003032100000).
4. The increase in vacuum acting on EGR valve diaphragm overcomes valve spring and begins to lift EGR valve pintle off its seat, causing exhaust gas to flow into intake manifold.
5. Exhaust gas flowing through EGR valve must first pass through EGR metering orifice (orifice tube). With one side of orifice exposed to exhaust backpressure and other to intake manifold, a pressure drop is created across orifice whenever there is EGR flow. When EGR valve closes, there is no longer flow across metering orifice and pressure on both sides of orifice is the same. PCM constantly targets a desired pressure drop across metering orifice to achieve desired EGR flow. For additional orifice tube assembly information, see «ORIFICE TUBE ASSEMBLY»(ref-153170-S15623207612003032100000).
6. DPFE EGR sensor measures actual pressure drop across metering orifice and relays a proportional voltage signal between 0-5 volts to PCM. (Scheme 83) PCM uses this feedback signal to correct for any errors in achieving desired EGR flow. For additional DPFE EGR sensor information, see «REMOTE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR»(ref-153170-S11561378592003032100000) or «TUBE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR»(ref-153170-S37648975652003032100000).

Scheme 82

Scheme 83

Differential Pressure Feedback EGR Sensor (Remote Mounted)

Differential Pressure Feedback (DPFE) EGR sensor is a ceramic, capacitive type pressure transducer that monitors differential pressure across a metering orifice located in orifice tube assembly. DPFE EGR sensor receives this signal through 2 hoses referred to as downstream pressure hose (REF), and upstream pressure hose (HI). HI and REF hose connections are marked on aluminum DPFE EGR sensor housing for identification. Note that HI uses a larger diameter hose. DPFE EGR sensor outputs a voltage proportional to pressure drop across metering orifice and supplies it to PCM as EGR flow rate feedback. (Scheme 84)

Scheme 84

Differential Pressure Feedback EGR Sensor (Tube Mounted)

Tube mounted DPFE EGR sensor is identical in operation as remote mounted larger metal or plastic DPFE sensors and uses a one volt offset. HI and REF hose connections are marked on underside of sensor. (Scheme 85)

Scheme 85

Vacuum regulator solenoid is an electromagnetic device used to regulate vacuum supply to the EGR valve. EGR vacuum regulator solenoid contains a coil which magnetically controls the position of a disk to regulate the vacuum. As the duty cycle to coil increases, vacuum signal passed through the EGR vacuum regulator solenoid to the EGR valve also increases. Vacuum not directed to the EGR is vented to atmosphere. At zero percent duty cycle (no electrical signal applied), EGR vacuum regulator solenoid allows some vacuum to pass, but not enough to open EGR valve.

EGR Valve

EGR valve in the DPFE EGR system is a conventional, vacuum actuated EGR valve. The valve increases or decreases flow of exhaust gas recirculation. As vacuum applied to EGR valve diaphragm overcomes spring force, valve begins to open. As vacuum signal weakens, at 1.6 in. Hg (5.4 kPa) or less, spring force closes valve. EGR valve is fully open at about 4.5 in. Hg (15 kPa). Since EGR flow requirement varies greatly, providing service specifications on flow rate is impractical. The OBD-II system monitors EGR valve function and triggers a DTC if test criteria is not met. EGR valve flow rate is not measured directly as part of field diagnostic procedures.

Electric EGR (EEGR) motor/valve system uses exhaust gas recirculation to control Oxides of Nitrogen (NOx) emissions just like vacuum operated systems. The difference is the way in which exhaust gas is controlled. Advantages to this type of system are

1. EEGR valve is activated by an electric stepper motor not a vacuum motor. It is located at rear of engine block.
2. No vacuum diaphragm is used.
3. No DPFE sensor is used.
4. No Orifice Tube Assembly is used.
5. No EGR vacuum regulator solenoid is used.
6. A new MAP sensor is used. A TMAP is used, but temperature function is not used at this time. TMAP is located on top of valve cover.
7. Engine coolant is routed through the assembly, extending durability of electric motor.

EEGR system consists of an electric EGR motor/valve integrated assembly, a PCM, TMAP sensor and connecting wiring. The following list of components and their specific operation corresponds to numbers in illustration. (Scheme 86)

1. EEGR system receives signals from Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor, Crankshaft Position (CKP) sensor and Thermal Manifold Absolute Pressure (TMAP) sensor to provide information on engine operating conditions to PCM. Engine must be warm, stable and running at a moderate load and engine speed (RPM) before EEGR system is activated. PCM will deactivate EGR during idle, extended Wide Open Throttle (WOT), or whenever a failure is detected in an EEGR component or EGR required input.
2. PCM calculates desired amount of EGR for a given set of engine operating conditions.
3. PCM in turn will output signals to EEGR motor to move (advance or retract) a certain number of discrete steps. Electric stepper motor will directly actuate EGR valve, independent of engine vacuum. EGR valve is commanded from 0-52 discrete increments or "steps" to move EGR valve from a fully closed to full or partially open position. The position of EGR valve determines EGR flow.
4. TMAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into intake manifold. Variations in EGR being used will correlate to TMAP signal. Increasing EGR will increase manifold pressure values.

EEGR valve is a water cooled motor/valve assembly. (Scheme 87)and (Scheme 88). The motor is commanded to move in 52 discrete steps as it acts directly on EGR valve. Position of valve determines rate of EGR flow. The built in spring works to close valve against motor opening force.

Scheme 86

Scheme 87

Scheme 88

The ESM EGR system is an updated DPFE system. It functions in the same manner as the conventional DPFE system, however the various system components have been integrated into a single component called the EGR System Module (ESM). (Scheme 89)and (Scheme 90). The flange of the valve portion of the ESM bolts directly to the intake manifold with a metal gasket that forms the measuring orifice. This arrangement increases system reliability and response time. By relocating the EGR orifice from the exhaust to the intake side of the EGR valve, the downstream pressure signal measures Manifold Absolute Pressure (MAP). The system provides the PCM with a differential DPFE signal, identical to the traditional DPFE system.

The Delta Pressure Feedback EGR Monitor is a series of electrical tests and functional tests that monitor various aspects of EGR system operation.

First, the Delta Pressure Feedback EGR (DPFE) sensor input circuit is checked for out of range values (P1400/P0405 and P1401/P0406). The Electronic Vacuum Regulator (EVR) output circuit is checked for opens and shorts (P1409/P0403).

EGR normally has large amounts of water vapor that are the result of the engine combustion process. During cold ambient temperatures, under some circumstances, water vapor can freeze in the DPFE sensor, hoses, as well as other components in the EGR system. In order to prevent MIL illumination for temporary freezing, the following logic is used

1. If an EGR system malfunction is detected above 32°F, the EGR system and the EGR monitor is disabled for the current driving cycle. A DTC is stored and the MIL is illuminated if the malfunction has been detected on two consecutive driving cycles.
2. If an EGR system malfunction is detected below 32°F, only the EGR system is disabled for the current driving cycle. A DTC is not stored and the I/M readiness status for the EGR monitor will not change. The EGR monitor, however, will continue to operate. If the EGR monitor determined that the malfunction is no longer present (i.e., the ice melts), the EGR system will be enabled and normal system operation will be restored.

After the vehicle is started, during vehicle acceleration, the differential pressure indicated by the DPFE sensor at zero EGR flow is checked to ensure that both hoses to the DPFE sensor are connected. Under this condition, the differential pressure should be zero. If the differential pressure indicated by the DPFE sensor exceeds a maximum threshold or falls below a minimum threshold, an upstream or downstream DPFE hose malfunction is indicated (P1405 P1406).

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the low flow check is performed. Since the EGR system is a closed loop system, the EGR system will deliver the requested EGR flow as long as it has the capacity to do so. If the EVR duty cycle is very high (greater than 80% duty cycle), the differential pressure indicated by the DPFE sensor is evaluated to determine the amount of EGR system restriction. If the differential pressure is below a calibratable threshold, a low flow malfunction in indicated (P0401/P0406).

Finally, the differential pressure indicated by the DPFE sensor is also checked at idle with zero requested EGR flow to perform the high flow check. If the differential pressure exceeds a calibratable limit, it indicates a stuck open EGR valve or debris temporarily lodged under the EGR valve seat (P0402).

If the inferred ambient temperature is less than 32°F, or greater than 140°F, or the altitude is greater than 8,000 feet (BARO less than 22.5 in. Hg), the EGR monitor cannot be run reliably. In these conditions, a timer starts to accumulate the time in these conditions. If the vehicle leaves these extreme conditions, the timer starts decrementing, and, if conditions permit, will attempt to complete the EGR flow monitor. If the timer reaches 500 seconds, the EGR monitor is disabled for the remainder of the current driving cycle and the EGR Monitor I/M Readiness bit will be set to a "ready" condition after one such driving cycle. Vehicles will require two such driving cycles for the EGR Monitor I/M Readiness bit to be set to a "ready" condition.

Scheme 89

Scheme 90

Malfunction Indicator Light (MIL) alerts the driver that PCM has detected an OBD-II emission related component or system fault. When this occurs, an OBD-II DTC will be set. MIL is located on instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or uses an ISO standard engine symbol. (Scheme 91) Power is supplied to MIL whenever ignition switch is in RUN or START position. MIL will remain ON in RUN or START mode as a bulb check during instrument cluster proveout for about 4 seconds. MIL will remain on after bulb check for the following reasons

1. PCM illuminates MIL for an emission related concern and a DTC will be present.
2. Instrument cluster will illuminate MIL if PCM does not send a control message to instrument cluster.
3. PCM is operating in Hardware Limited Operation Strategy (HLOS). See «HARDWARE LIMITED OPERATION STRATEGY»(ref-153170-S09191290582003032100000) under POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS.
4. MIL circuit is shorted to ground.

If MIL remains off (during bulb check), possible causes are; bulb is damaged or MIL circuit is open. To turn off the MIL after a repair, a reset command from scan tool must be sent, or 3 consecutive drive cycles must be completed without a fault. If MIL blinks at a steady rate, a severe misfire condition could possibly exist. If MIL blinks erratically, an intermittent open in B+ circuit to bulb or an intermittent short to ground in MIL circuit may exist. Also, PCM can reset while cranking if battery voltage is low.

Scheme 91

ELECTRONIC THROTTLE BODY

The Gen II electronic throttle body has the following characteristics

1. The DC motor is driven by the PCM (requires two wires). The gear ratio from the motor to the throttle plate shaft is 17:1.
2. There are two designs; parallel and in-series. The parallel design has the motor under the bore parallel to the plate shaft. The motor housing is integrated into the main housing (in general this is more difficult to package). The in-series design has a separate motor housing that protrudes out and offers more packaging flexibility.
3. Two springs are used: one is used to close the throttle (main spring) and the other is in a plunger assembly that results in a default angle with no power applied. This is for limp home reasons (force of plunger spring is 2X main spring). Default angle is usually set to result in a top vehicle speed of 30 MPH (typically 7 to 8 degrees from hard-stop angle).
4. The closed throttle plate hard stop is used to avoid the throttle from binding is the bore (about 0.75 degree). This hard stop is non-adjustable and is set to result in less airflow than the minimum engine airflow required at idle.
5. Unlike cable type throttle bodies, the intent for the ETB is not to have a hole in the plate or use plate sealant. The hole in the plate is not required with ETB because the required idle airflow is provided by the plate angle, which also is the reason there is no IAC.
6. The system has two throttle position sensors. Redundant throttle position signals are required for monitor reasons. TP1 has a negative slope (increasing angle, decreasing voltage) and TP2 has a positive slope (increasing angle, increasing voltage). During normal operation the negative sloped TP sensor (TP1) is used by the control strategy as the indication of throttle position. The TP assembly requires four wires: 5 V Reference Voltage Signal Return (ground) TP1 voltage with negative voltage slope (5-0) TP2 voltage with positive voltage slope (0-5)

ACCELERATOR PEDAL POSITION SENSORS

The ETC strategy uses pedal position sensors as an input to determine the driver demand.

1. There are three pedal position sensors required for safety monitor reasons. APP1 has a negative slope (increasing angle, decreasing voltage) and APP2 & APP3 both have a positive slope (increasing angle, increasing voltage). During normal operation APP1 is used as the indication of pedal position by the strategy.
2. There are two VREF wires, two signal return wires and three signal wires (total of seven wires and pins) between the PCM and APPS assembly. 2-5 V Reference Voltage. 2-Signal Return "ground". APP1 voltage with negative voltage slope (5-0). APP2 voltage with positive voltage slope (0-5). APP3 voltage with positive voltage slope (0-5).
3. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then converts these degrees to counts, which is the input to the torque based strategy.
4. The three pedal position signals ensure a correct input to the PCM, if any one signal has a fault. The PCM knows if a signal is wrong by calculating where it should be, inferred by the other signals. A safe value will be substituted for a faulty signal if two out of the three signals are bad.

Scheme 92

PCM controlled charging system provides improved battery life and improved engine performance. PCM controlled generator regulator voltage set point is determined by PCM and communicated to the regulator by the Generator Communication (GEN COM) circuit. PCM will use a calibratable algorithm to estimate battery temperature, reducing damage to battery by overcharging or undercharging. At Wide Open Throttle (WOT), PCM will momentarily lower the regulator voltage set point, reducing torque load on engine and improving acceleration. PCM has a calibratable time limit on the reduced voltage feature to prevent decreased generator output for an extended WOT period, which may cause battery discharge.

Generator Load Input (GLI) circuit is used by PCM to determine generator load on engine. As generator load increases, PCM will adjust idle speed accordingly. This helps reduce idle surges due to switching high current loads. GLI signal is sent to PCM from voltage regulator/generator. GLI signal is a variable frequency duty cycle. Normal operating frequency is 40-250 Hz. Normal signal DC voltage (referenced to ground) is between 1.5 volts (low generator load) and 10.5 volts (high generator load).

The regulator uses a Generator Monitor (GEN MON) signal to provide feedback to Powertrain Control Module (PCM) with charging system information. GEN MON signal lets PCM know when the charging system receives a transient electrical load which would normally affect idle stability. Because PCM can anticipate additional loads, PCM can choose to reduce regulator set point or increase engine idle speed, both of which are calibratable features. Charge indicator will be illuminated if PCM fails to see a signal on generator monitor line for a time period greater than 500 milliseconds. This telltale command will also be used to indicate over-voltage conditions detected by PCM controlled generator.

CARS

1. On Crown Victoria, see «ENGINE PERFORMANCE»(ref-154364-S30294725172003051400000) in SYSTEM WIRING DIAGRAMS article.
2. On Focus, see «ENGINE PERFORMANCE»(ref-154425-S07468081362003051400000) in SYSTEM WIRING DIAGRAMS article.
3. On Grand Marquis, see «ENGINE PERFORMANCE»(ref-154406-S03975765212003051400000) in SYSTEM WIRING DIAGRAMS article.
4. On LS, see «ENGINE PERFORMANCE»(ref-154424-S20020034772003051400000) in SYSTEM WIRING DIAGRAMS article.
5. On Marauder, see «ENGINE PERFORMANCE»(ref-154433-S13321705662003051400000) in SYSTEM WIRING DIAGRAMS article.
6. On Mustang, see «ENGINE PERFORMANCE»(ref-154340-S15212209392003051400000) in SYSTEM WIRING DIAGRAMS article.
7. On Sable, see «ENGINE PERFORMANCE»(ref-154408-S21196731022003051400000) in SYSTEM WIRING DIAGRAMS article.
8. On Taurus, see «ENGINE PERFORMANCE»(ref-154346-S41000750532003051400000) in SYSTEM WIRING DIAGRAMS article.
9. On Thunderbird, see «ENGINE PERFORMANCE»(ref-154347-S15764185652003051400000) in SYSTEM WIRING DIAGRAMS article.
10. On Town Car, see «ENGINE PERFORMANCE»(ref-154332-S36162759332003051400000) in SYSTEM WIRING DIAGRAMS article.
11. On ZX2, see «ENGINE PERFORMANCE»(ref-154434-S05219728512003051400000) in SYSTEM WIRING DIAGRAMS article.

TRUCKS

1. On Aviator, see «ENGINE PERFORMANCE»(ref-154449-S30952553792003051400000) in SYSTEM WIRING DIAGRAMS article.
2. On Cab and Chassis F350 Super Duty, see «ENGINE PERFORMANCE»(ref-154363-S18748364512003051400000) in SYSTEM WIRING DIAGRAMS article.
3. On Cutaway E350 Super Duty, see «ENGINE PERFORMANCE»(ref-154333-S04450249282003051400000) in SYSTEM WIRING DIAGRAMS article.
4. On Econoline E150, see «ENGINE PERFORMANCE»(ref-154334-S10462385272003051400000) in SYSTEM WIRING DIAGRAMS article.
5. On Econoline E250, see «ENGINE PERFORMANCE»(ref-154335-S16491182962003051400000) in SYSTEM WIRING DIAGRAMS article.
6. On Econoline E350 Super Duty, see «ENGINE PERFORMANCE»(ref-154336-S11415451512003051400000) in SYSTEM WIRING DIAGRAMS article.
7. On Escape, see «ENGINE PERFORMANCE»(ref-154430-S08155773812003051400000) in SYSTEM WIRING DIAGRAMS article.
8. On Expedition, see «ENGINE PERFORMANCE»(ref-154337-S37422994292003051400000) in SYSTEM WIRING DIAGRAMS article.
9. On Explorer, see «ENGINE PERFORMANCE»(ref-154339-S21010081492003051400000) in SYSTEM WIRING DIAGRAMS article.
10. On Explorer Sport, see «ENGINE PERFORMANCE»(ref-154432-S32262993312003051400000) in SYSTEM WIRING DIAGRAMS article.
11. On Explorer Sport Trac, see «ENGINE PERFORMANCE»(ref-154429-S34302365642003051400000) in SYSTEM WIRING DIAGRAMS article.
12. On Excursion, see «ENGINE PERFORMANCE»(ref-154426-S21967319832003051400000) in SYSTEM WIRING DIAGRAMS article.
13. On E450 Super Duty, see «ENGINE PERFORMANCE»(ref-154453-S37520167922003051400000) in SYSTEM WIRING DIAGRAMS article.
14. On E550 Super Duty, see «ENGINE PERFORMANCE»(ref-154456-S36775797642003051400000) in SYSTEM WIRING DIAGRAMS article.
15. On F450 Super Duty, see «ENGINE PERFORMANCE»(ref-154454-S19299036622003051400000) in SYSTEM WIRING DIAGRAMS article.
16. On F550 Super Duty, see «ENGINE PERFORMANCE»(ref-154455-S23398037162003051400000) in SYSTEM WIRING DIAGRAMS article.
17. On Mountaineer, see «ENGINE PERFORMANCE»(ref-154407-S09318122352003051400000) in SYSTEM WIRING DIAGRAMS article.
18. On Navigator, see «ENGINE PERFORMANCE»(ref-154331-S09556899652003051400000) in SYSTEM WIRING DIAGRAMS article.
19. On Pickup F150, see «ENGINE PERFORMANCE»(ref-154341-S02719138532003051400000) in SYSTEM WIRING DIAGRAMS article.
20. On Pickup F250 Super Duty, see «ENGINE PERFORMANCE»(ref-154342-S17416650412003051400000) in SYSTEM WIRING DIAGRAMS article.
21. On Pickup F350 Super Duty, see «ENGINE PERFORMANCE»(ref-154343-S34121943772003051400000) in SYSTEM WIRING DIAGRAMS article.
22. On Ranger, see «ENGINE PERFORMANCE»(ref-154344-S07083847482003051400000) in SYSTEM WIRING DIAGRAMS article.
23. On RV Cutaway E350 Super Duty, see «ENGINE PERFORMANCE»(ref-154345-S25603007422003051400000) in SYSTEM WIRING DIAGRAMS article.
24. On Windstar, see «ENGINE PERFORMANCE»(ref-154348-S23364496442003051400000) in SYSTEM WIRING DIAGRAMS article.