Engine Controls - Theory & Operation - Except Diesel Ford Econoline I

INTRODUCTION

Note. Information for Escort applies to Escort ZX2 unless otherwise indicated.

This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.

POWERTRAIN CONTROL MODULE (PCM)

PCM monitors engine operating conditions by input received from engine sensors. Control of output actuators determines fuel mixture and idle speed. For PCM location, see POWERTRAIN CONTROL MODULE LOCATION table.

The engine control system consists of the PCM, relays, modules, sensors, switches and actuators. The PCM sends out electrical reference signals to engine sensors and then analyzes the return signals. The engine sensors supply the PCM with specific information, in the form of electrical signals, to determine engine operating conditions.

In the event of a sensor or actuator failure, the PCM initiates an alternative strategy called Failure Mode Effects Management (FMEM) to allow the vehicle to maintain driveability. In the event of PCM failure, Hardware Limited Operation Strategy (HLOS) will be activated. HLOS is a system of alternate circuitry that provides minimal engine operation if the PCM fails. During HLOS, all self-test function will stop and system will be controlled by electronic hardware.

Malfunction Indicator Light (MIL) will remain on whenever FMEM or HLOS is in operation. FMEM and HLOS substitute a fixed signal and continue to monitor system failure. If signal(s) return to within operating limits, PCM will resume normal operation.

POWERTRAIN CONTROL MODULE LOCATION

CONSTANT CONTROL RELAY MODULE (CCRM)

CCRM interfaces with the PCM to control cooling fan, A/C clutch and fuel pump operation. The CCRM also incorporates electronic engine control power relay to supply power to the EEC-V system See CCRM LOCATIONS table.

CCRM LOCATIONS

FUEL PUMP DRIVER MODULE (FPDM)

FPDM receives a duty cycle signal from the PCM and controls fuel pump operation. This results in variable speed fuel pump operation. FPDM uses the fuel pump monitor circuit to send diagnostic information to the PCM.

NATURAL GAS (NG) VEHICLE MODULE

NG vehicle module has 2 functions. The first function is to operate fuel injectors and is referred to as Injector Driver Module (IDM). The second function is to control fuel gauge and is referred to as Fuel Indicator Module (FIM). See NATURAL GAS VEHICLE MODULE LOCATIONS table.

NATURAL GAS VEHICLE MODULE LOCATIONS

INPUT DEVICES

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

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 appropriate wiring diagram in WIRING DIAGRAMS article. The available input signals include the following

A/C Cycling Switch (ACCS)

The ACCS circuit provides a voltage signal to the PCM that indicates when A/C is requested. When A/C demand switch is in the ON position, and both the ACCS and the high pressure switch (if equipped) contacts are closed, voltage is supplied to the ACCS circuit at the PCM. If ACCS signal is not received by the PCM, the PCM will not allow A/C to operate.

A/C Pressure Sensor

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

A/C High Pressure Switch

The A/C high pressure switch is used for additional A/C system pressure control. Switch is either dual function for 2-speed fan control applications or single function for all other applications. For fan control, the normally open pressure contacts close at a predetermined A/C pressure. This grounds the ACPSW circuit input to the PCM. The PCM will then turn on the high speed fan to help reduce A/C pressure.

Brake Pedal Position (BPP) Switch

BPP switch is wired to brakelight circuit. It signals the PCM when the brake is applied. The BPP input is used to adjust engine idle when A/C is in use and to control torque converter clutch lock/unlock strategy.

Camshaft Position (CMP) Sensor

A 3-pin Hall Effect type sensor or a 2-pin variable reluctance CMP sensor is used. CMP sensor is used to determine camshaft position and to identify when piston No. 1 is at TDC of compression stroke. CMP sensor signal is used by PCM for synchronizing firing of sequential fuel injectors. Models with Coil On Plug (COP) ignition also use CMP signal to select the proper ignition coil to fire.

Clutch Pedal Position (CPP) Switch

CPP switch is mounted near clutch pedal. CPP switch indicates clutch pedal position by means of an on/off switch signal. This signal is used by PCM to determine clutch pedal position and on some models, gear shift selector position.

Crankshaft Position (CKP) Sensor

CKP sensor is a magnetic transducer mounted on engine block, next to crankshaft pulse wheel. By monitoring pulse wheel, the CKP sensor indicates crankshaft position and speed information to PCM.

Cylinder Head Temperature (CHT) Sensor

CHT sensor is the input signal used for the cooling system fail-safe strategy. CHT sensor signals PCM to activate fail-safe strategy if cylinder head temperature exceeds preprogrammed conditions.

Differential Pressure Feedback EGR (DPFE) Sensor

See EGR SYSTEM under EMISSION SYSTEMS.

Engine Coolant Temperature (ECT) Sensor

ECT sensor is a thermistor which changes resistance proportionate to temperature changes. ECT sensor inputs coolant temperature to the PCM. ECT sensor is threaded into heater outlet fitting or coolant passage.

Engine Fuel Temperature (EFT) Sensor

EFT sensor is a thermistor device which changes resistance proportionate to temperature changes. The EFT sensor inputs fuel temperature of fuel near fuel injectors to the PCM. Signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.

Flex Fuel (FF) Sensor

The FF sensor is a capacitive device with a signal processing stage whose frequency varies with dielectric constant, conductivity and temperature of the methanol gasoline fuel mixture in its measuring cell.

As the percentage of methanol in fuel mixture increases, the output frequency of the FF sensor signal will increase. A fuel mixture with 30 percent methanol will have a FF sensor signal output frequency of 60-100 Hz. A fuel mixture with 60 percent methanol will have a FF sensor signal output frequency of 90-130 Hz. The PCM uses the data to calculate correct air/fuel ratio and ignition spark advance.

Fuel Pump Monitor (Models Without Fuel Pump Driver Module)

The Fuel Pump Monitor (FPM) circuit is spliced into the Fuel Pump Power (FP PWR) circuit and used by the PCM for diagnostic purposes. The PCM sources a low current voltage down the FPM circuit.

With the fuel pump off, voltage is pulled low by the path to ground through the fuel pump. With fuel pump off and the FPM circuit low, the PCM can verify the FPM circuit and FP PWR circuit are complete from the FPM splice through the fuel pump to ground.

With the fuel pump on, voltage is supplied from the fuel pump relay to the FP PWR and FPM circuits. With the 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 Pump Monitor (Models With Fuel Pump Driver Module)

The Fuel Pump Driver Module (FPDM) communicates diagnostic information to the PCM through the Fuel Pump Monitor (FPM) circuit. This information is sent to the PCM as a duty cycle signal. PCM uses this signal to verify FPDM is powered and able to communicate on the FPM circuit.

Fuel Rail Pressure (FRP) Sensor

FRP sensor changes resistance proportionate to pressure changes. The FRP sensor inputs fuel pressure (near fuel injectors) to the PCM. Signal is used by PCM to adjust fuel injector pulse width and meter fuel to each cylinder.

Heated Oxygen Sensor (HO2S)

The heated oxygen sensors are mounted in the exhaust manifold and pipe. (Scheme 4) HO2S sensor uses a built-in heating circuit. The heating circuit is used to bring the HO2S sensor up to operating temperature, enabling faster conversion to closed-loop operation.

HO2S monitors oxygen content of exhaust gases. When HO2S is at operating temperature, a voltage signal is produced, which varies according to oxygen content of exhaust gases. Signal is transmitted to the PCM and is translated into a rich or lean mixture signal.

Scheme 4

Intake Air Temperature (IAT) Sensor

IAT sensor is a thermistor which changes resistance in proportion to temperature changes. IAT sensor inputs air temperature to the PCM. The IAT sensor provides a quicker temperature change response time than the ECT sensor.

Mass Airflow (MAF) Sensor

MAF sensor uses 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 5)

The current required to maintain hot wire operating temperature is proportional to the intake air mass. The PCM uses this current requirement to calculate the fuel injector pulse width in order to provide the desired air/fuel ratio.

Scheme 5

Park/Neutral Position (PNP) Switch

PNP switch is mounted on transmission selector lever. PNP switch indicates shift lever position by means of a variable resistance signal. This signal is used by PCM to determine gear shift selector position.

Power Steering Pressure (PSP) Sensor

The PSP sensor monitors power steering pressure. When power steering fluid pressure exceeds the preset limit, the PSP sensor sends an input signal to the PCM. The PCM then adjusts idle speed. PCM also uses PSP signal to adjust transmission Electronic Pressure Control (EPC) pressure during increased engine load.

Power Steering Pressure (PSP) Switch

The PSP switch monitors power steering pressure. PSP switch is normally closed and opens as pressure increases. PCM uses input signal from PSP switch to compensate for additional loads on engine by adjusting idle speed. PCM also uses PSP signal to adjust transmission Electronic Pressure Control (EPC) pressure during increased engine load.

Power Take-Off (PTO) Switch

The PTO circuit is used to disable some of the OBD-II monitors during PTO operation. The switch is normally open and circuit voltage is normally low. When switch is closed, battery voltage is supplied to the circuit, indicating an additional load condition to PCM.

Throttle Position (TP) Sensor

TP sensor is a rotary potentiometer or Hall Effect sensor that monitors throttle plate opening. TP sensor signal to the PCM is proportional to throttle plate opening angle and rate of angle change. The TP sensor signal affects air/fuel ratio, injector timing, idle speed, EGR flow and ignition timing. The TP sensor is mounted on throttle body.

Transmission Control Switch (TCS)

TCS position is controlled by vehicle operator. When equipped, the Transmission Control Indicator Light (TCIL) will come on when the TCS is cycled to disengage overdrive.

Transmission Fluid Temperature (TFT) Sensor

TFT sensor is a thermistor that changes resistance as transmission fluid temperature changes. Sensor resistance decreases as fluid temperature increases. Sensor resistance variation is converted into a voltage signal and sent to the PCM. The PCM uses this input signal to determine transmission fluid temperature.

Vehicle Speed Sensor (VSS)

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. The PCM uses this signal to control fuel injection, ignition timing and transmission shift points.

OUTPUT SIGNALS

Note. 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 Purge (CANP) Solenoid Valve

See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.

EGR Vacuum Regulator Solenoid

See EGR SYSTEM under EMISSION SYSTEMS.

EGR Valve

See EGR SYSTEM under EMISSION SYSTEMS.

Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM (GASOLINE) or FUEL SYSTEM (NATURAL GAS) .

Fuel Pump (Gasoline Models Only)

See FUEL DELIVERY under FUEL SYSTEM (GASOLINE) .

Fuel Rail Shutoff Valve

See FUEL DELIVERY under FUEL SYSTEM (NATURAL GAS) .

Fuel Valve Relay

See FUEL DELIVERY under FUEL SYSTEM (NATURAL GAS) .

Idle Air Control (IAC) Valve

See IDLE SPEED under FUEL SYSTEM (GASOLINE) or FUEL SYSTEM (NATURAL GAS) .

Intake Manifold Runner Control (IMRC)

The air induction system improves engine performance by using the IMRC assemblies as follows

1. The lower intake manifold has two runners per cylinder, feeding each of the intake ports in the cylinder heads.
2. The IMRC assemblies are located between the upper intake manifold and cylinder heads, providing two air passages for each cylinder.
3. One air passage is always open and the other passage switches from closed to open by means of a valve plate. Below 2450 rpm, this valve plate is closed to improve fuel economy and emissions. Above 2450 rpm, this valve plate opens to improve high speed engine performance.

The valve plates are opened and closed by the IMRC electric actuator, which is controlled by the PCM.

Malfunction Indicator Light (MIL)

See SELF-DIAGNOSTIC SYSTEM .

FUEL DELIVERY

Three types of fuel systems are used: returnable, mechanical returnless and electronic returnless.

FUEL SYSTEM IDENTIFICATION

Fuel Pump (Returnable Fuel System)

Fuel is supplied by in-tank electric fuel pump. (Scheme 6) Pump also has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Pump delivers fuel from fuel tank through fuel filter to fuel supply manifold. Fuel charging manifold assembly incorporates electrically actuated fuel injectors directly above each intake port. Injectors spray metered quantity of fuel into intake airstream. Constant fuel pressure is maintained to injector nozzles by fuel pressure regulator located on fuel supply manifold.

Scheme 6

Fuel Pump (Mechanical Returnless Fuel System)

Fuel is supplied by an in-tank electric fuel pump. (Scheme 7) Pump also has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Pump delivers fuel from fuel tank through fuel filter and fuel rail pulse damper to fuel charging manifold assembly. Fuel charging manifold assembly incorporates electrically actuated fuel injectors directly above each intake port. Injectors spray metered quantity of fuel into intake airstream. Constant fuel pressure is maintained to injector nozzles by fuel pressure regulator located in fuel tank, attached to fuel pump.

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.

Scheme 7

Fuel Pump (Electronic Returnless Fuel System)

Fuel is supplied by an in-tank electric fuel pump. (Scheme 8) Pump also has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. Pump delivers fuel from fuel tank through fuel filter to fuel charging manifold assembly. Fuel charging manifold assembly incorporates electrically actuated fuel injectors directly above each intake port. Injectors spray metered quantity of fuel into intake airstream.

Scheme 8

Fuel Pressure Regulator (Returnable Fuel System)

Fuel pressure regulator controls fuel pressure supplied to injectors. Fuel pressure regulator is attached to fuel supply manifold assembly, downstream of fuel injectors. Regulator is diaphragm operated. One side of diaphragm senses fuel pressure, and other side is subjected to intake manifold pressure. (Scheme 9)

Fuel pressure is controlled by spring preload applied to diaphragm. Balancing one side of diaphragm with manifold pressure maintains constant fuel pressure at injectors. Excess fuel supplied by pump, but not consumed by engine, passes through regulator and returns to fuel tank through fuel return line.

Scheme 9

Fuel Pressure Regulator (Mechanical Returnless Fuel System)

Fuel pressure regulator controls fuel pressure supplied to injectors. Fuel pressure regulator is located in fuel tank, attached to fuel pump assembly. (Scheme 7) Fuel pressure regulator is a diaphragm operated relief valve. Fuel pressure is controlled by spring preload applied to diaphragm. Excess fuel is by-passed through the regulator and returned to fuel tank.

Fuel Pressure Regulator (Electronic Returnless Fuel System)

Electronic returnless fuel system does not use a fuel pressure regulator. Electronic returnless fuel system uses a Fuel Rail Pressure (FRP) sensor to sense fuel pressure. FRP sensor is located in fuel supply manifold assembly. FRP sensor input signal is used by the PCM to vary the duty cycle output to the Fuel Pump Driver Module (FPDM) to compensate for varying loads. FPDM then modulates voltage to fuel pump to achieve proper fuel pressure. Engine Fuel Temperature (EFT) sensor input signal is also used by PCM to vary fuel pressure to avoid fuel system vaporization.

Inertia Fuel Shutoff (IFS) Switch (All Fuel Systems)

In the event of a collision or vehicle rollover, electrical contacts within the inertia switch trip open and voltage supply to the electric fuel pump is shut off. If the electrical circuit trips, 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 10)

Scheme 10

The PCM controls fuel injector pulse width ("on" time) to meter fuel quantity into intake ports. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain correct air/fuel ratio throughout entire engine operating range. Injector on time (pulse width) is the only controlled variable in fuel delivery system.

Each cylinder has a solenoid-operated injector that sprays fuel toward the back of each intake valve. Fuel injector nozzles are solenoid-operated valves, which meter and atomize fuel delivered to engine. Each injector receives battery voltage through an ignition switch circuit. The PCM-controlled ground circuit is used to complete the circuit and energize the injector.

Injector bodies consist of solenoid-actuated pintle and needle valve assembly. Injector flow orifice is fixed and fuel pressure at injector tip is constant. Fuel flow to engine is regulated according to length of time solenoid is energized. Atomized spray pattern is obtained by shape of pintle.

Idle Air Control (IAC) Valve Assembly

IAC valve assembly is used to control idle speed and provide a dashpot function. IAC valve assembly meters inlet air around the throttle plate through a by-pass within the IAC valve assembly and throttle body. (Scheme 11)or (Scheme 12).

The PCM determines desired idle speed or air by-pass and signals the IAC valve assembly through specified duty cycle. The IAC solenoid is built into IAC valve assembly. IAC solenoid responds by positioning the IAC valve to control amount of air by-passed. PCM monitors engine speed and adjusts IAC duty cycle to achieve desired RPM. IAC valve assembly is not adjustable and cannot be cleaned.

Scheme 11

Scheme 12

Fuel system consists of fuel tank(s), fuel shutoff valve assemblies, fuel supply lines, fuel filter, manual shutoff valve(s), fuel rail and fuel pressure regulator.

Fuel Tank Shutoff Valve

The fuel tank shutoff valve is located on end of fuel tank. Fuel tank shutoff valve logic is defined in the fuel system control strategy and is executed in the PCM.

The fuel valve relay has a primary and a secondary circuit. The primary circuit is controlled by the PCM. The secondary circuit provides battery power to the fuel shutoff valve circuit when relay is energized.

The fuel rail shutoff valve is a normally closed valve that opens when grounded by PCM. Fuel rail shutoff valve isolates fuel injectors from fuel line pressure when engine is not running. The fuel rail shutoff valve is wired in parallel with the fuel tank shutoff valves.

Fuel Pressure Regulator

Fuel pressure regulator is a single staged pressure reducing regulator that expands natural gas from stored pressures of 200-3000 psi (1379-20,685 kPa) to engine fuel injector pressures of 105-125 psi (724-862 kPa). Regulator contains a 275 psi (1896 kPa) check valve that protects the low pressure system. When natural gas expands, fuel temperature decreases causing extreme cold temperatures. To prevent damaging fuel system components, engine coolant is routed through the pressure regulator to warm the fuel before it expands. The regulator has an internal thermostat to control engine coolant flow through the regulator. This prevents overheating and thinning of fuel which could cause lean combustion. When coolant temperature increases to about 100°F (82°C), regulator thermostat closes and outlet coolant flow is restricted.

Inertia Fuel Shutoff (IFS) Switch

In the event of a collision or vehicle rollover, electrical contacts within the inertia switch trip open and voltage supply to the electric fuel pump is shutoff. If the electrical circuit trips, 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 10) Some models are equipped with a fuel reset indicator light located on the instrument cluster.

The PCM controls fuel injector pulse width ("on" time) to meter fuel quantity into intake ports. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain correct air/fuel ratio throughout entire engine operating range. Injector on time pulse width is the only controlled variable in fuel delivery system.

Each cylinder has a solenoid-operated injector that sprays fuel toward the back of each intake valve. Fuel injector nozzles are solenoid-operated valves which meter and atomize fuel delivered to engine. Each injector receives battery voltage through an ignition switch circuit. The PCM-controlled ground circuit is used to complete the circuit and energize the injector.

Flow capacity of natural gas fuel injectors is 6-12 times greater than typical gasoline fuel injectors. Also, injector resistance (4-6 ohms) is less than gasoline fuel injectors (11-18 ohms). To accommodate the lower resistance, a fuel injector driver module (also referred to as natural gas vehicle module) is used to convert the PCM fuel injector driver signal to a signal required by fuel injector.

IAC valve assembly is used to control idle speed and provide a dashpot function. IAC valve assembly meters inlet air around the throttle plate through a by-pass within the IAC valve assembly and throttle body. (Scheme 11)or (Scheme 12).

The PCM determines desired idle speed or air by-pass and signals the IAC valve assembly through specified duty cycle. The IAC solenoid is built into IAC valve assembly. IAC solenoid responds by positioning the IAC valve to control amount of air by-passed. PCM monitors engine speed and adjusts IAC duty cycle to achieve desired RPM. IAC valve assembly is not adjustable and cannot be cleaned.

ELECTRONIC IGNITION (EI) SYSTEM

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

Models Equipped With Coil Pack(s)

The EI system consists of a Crankshaft Position (CKP) sensor, coil pack(s), related wiring and PCM. The CKP sensor is used by the PCM to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted on front of crankshaft. The coil pack(s) receives its 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 strategy is reversed.

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.

Models Equipped With Coil On Plugs (COPs)

The EI system consists of a Crankshaft Position (CKP) sensor, Camshaft Position (CMP) sensor, individual COPs mounted directly on the spark plugs, related wiring and PCM. The CKP sensor is used by the 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 the 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 coils receive their signal from the PCM to fire at a calculated spark target. Only one coil is fired at a time and only on the compression stroke. The PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, 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.

Electronic Secondary Air Injection (AIR) System

The air injection system operates during the first 20-120 seconds of engine operation. Electronic AIR system consists of an electric air supply pump, single or dual Air Injection (AIR) diverter valve(s), AIR by-pass solenoid, solid state relay, related wiring and vacuum hoses. The electric air pump is controlled by signals from the PCM.

When the engine is started, PCM strategy determines when to enable the electronic air pump. The PCM signals the solid state relay and the AIR by-pass solenoid after a 5-10 second delay to begin system operation. Once the catalytic converter warms up, PCM then signals solid state relay to stop air pump operation and signals AIR by-pass solenoid to stop vacuum supply to AIR diverter valve(s).

EGR SYSTEM

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

System Description

The Differential Pressure Feedback EGR system controls oxides of nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to be reburned with the air/fuel charge. The EGR system consists of a differential pressure feedback EGR sensor, EGR valve, EGR vacuum regulator solenoid, orifice tube assembly, related wiring, PCM and vacuum hoses.

EGR valve is a conventional vacuum operated EGR valve. Vacuum to the EGR valve is controlled by a vacuum signal from EGR vacuum regulator solenoid. EGR valve should be closed at 1.6 in. Hg or less and fully open at 4.5 in. Hg.

Differential Pressure Feedback Sensor

Differential pressure feedback sensor is a ceramic, capacitive type pressure transducer that monitors the pressure difference across a metering orifice located in the orifice tube assembly. Sensor outputs a voltage signal to the PCM that is proportional to the pressure drop across the metering orifice. The PCM uses the voltage as feedback information on the rate of EGR flow. The PCM uses feedback to adjust the EGR vacuum solenoid and achieve the desired EGR flow.

Vacuum regulator solenoid is an electromagnetic device used to regulate vacuum supply to the EGR valve. 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 vacuum regulator solenoid to the EGR valve also increases. Vacuum not directed to the EGR is vented to atmosphere.

Orifice Tube Assembly

Orifice tube assembly is the section of tubing connecting exhaust system to intake manifold. Orifice tube provides flow path for the exhaust gas to the intake manifold. The orifice tube contains a metering orifice and 2 pressure pick-up tubes. (Scheme 13) The metering orifice creates a measurable pressure drop across it as the EGR valve opens and closes. The pressure differential across the orifice is picked up by the differential pressure feedback EGR sensor which provides feedback to PCM.

Scheme 13

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 3 different types of EVAP systems that may be used

1. Vapor Management Flow System
2. EVAP Running Loss System
3. On-Board Refueling Vapor Recovery EVAP System

Vapor Management Flow System

The vapor management flow system components consist of fuel tank, fuel filler cap, fuel vapor vent valve, EVAP canister, EVAP purge valve, related wiring and fuel vapor hoses. Vapor management flow system uses inputs from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Mass Airflow (MAF) sensor and Vehicle Speed Sensor (VSS) to provide information about engine operating conditions to PCM. Conditions necessary to activate vapor management flow system are: engine must be at normal operating temperature, engine must be operating under a moderate load, throttle must be open, and in close loop fuel control. The PCM deactivates vapor management flow system during idle or whenever a failure is detected.

1. EVAP Canister Purge Valve Normally closed purge valve controls the flow of fuel vapors from canister to intake manifold during various engine operating modes. When engine is shut off, vapors from fuel tank flow into canister. After engine is started, purge valve regulates fuel vapor flow by means of manifold vacuum and duty cycle signal from PCM.
2. Fuel Vapor Vent Valve Fuel Vapor in the fuel tank is vented to EVAP canister through the fuel vapor vent valve assembly. The fuel vapor vent valve is mounted in a rubber grommet in top of fuel tank. A vapor space between the fuel level and upper surface of fuel tank is combined with a small orifice and float shutoff (rollover) valve in the fuel vapor vent valve to prevent liquid fuel from passing into the EVAP canister. (Scheme 14)

Scheme 14

EVAP Running Loss System

The EVAP running loss system components consist of fuel tank, fuel filler cap, fuel tank mounted or in-line fuel vapor control valve, fuel vapor vent valve, EVAP canister, EVAP canister purge valve, fuel tank pressure sensor, canister vent solenoid, related wiring and fuel vapor hoses. EVAP running loss system uses inputs from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) 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 the PCM to determine activation of EVAP Monitor based on presence of fuel vapor or fuel sloshing.

1. Canister Vent (CV) Solenoid The CV solenoid seals the EVAP running loss system to atmosphere during the EVAP Running Monitor test.
2. Fuel Tank Pressure (FTP) Sensor The FTP sensor is used to measure fuel tank pressure during EVAP Monitor Running Monitor test. FTP sensor is also used to control excessive fuel tank pressure by forcing the system to purge.
3. EVAP Canister Purge Valve Normally closed purge valve controls the flow of fuel vapors from canister to intake manifold during various engine operating modes. When engine is shut off, vapors from fuel tank flow into canister. After engine is started, purge valve regulates fuel vapor flow by means of manifold vacuum and duty cycle signal from PCM.
4. Fuel Vapor Control Valve The fuel vapor control valve is used to close the flow of liquid fuel to the EVAP canister purge valve or EVAP canister during refueling. Fuel vapor control valve is also used to prevent accumulation of liquid fuel in the fuel vapor hoses caused by overfilling fuel tank. On Escort and Tracer, the fuel vapor control valve also contains a liquid/vapor fuel discriminator. Purpose of the liquid/vapor fuel discriminator is to separate the liquid and vapor state of the fuel at the fuel tank vent and allow only the fuel vapor to move through the EVAP running loss system with the liquid fuel remaining in the tank.
5. Fuel Vapor Vent Valve Fuel vapor vent valve assembly is mounted on top of fuel tank and is used to control flow of fuel vapor entering the fuel tank vapor delivery line to the EVAP canister. The head valve portion of the fuel vapor vent valve prevents fuel tank from overfilling during refueling. The fuel vapor vent valve also has a spring supported float that prevents liquid fuel from entering fuel tank vapor delivery line under severe handling or a vehicle rollover condition.
6. EVAP Canister Fuel Vapors from fuel tank are stored in EVAP canister. With engine running at RPM higher than idle, vapors are purged from EVAP canister back into the engine for combustion.

On-Board Refueling Vapor Recovery EVAP System

The on-board refueling vapor recovery EVAP system components consist of fuel tank, fuel filler cap, fuel filler pipe check valve/flapper valve, fuel tank pressure sensor, fuel vapor vent valve(s), EVAP canister(s), EVAP canister purge valve, canister vent solenoid, related wiring and fuel vapor hoses. (Scheme 15)or (Scheme 16).

1. Fuel Filler Pipe Check Valve The fuel filler pipe check valve on Crown Victoria, Grand Marquis, Sable 3.0L 2-Valve, Taurus 3.0L 2-Valve and Town Car is located inside fuel filler pipe. (Scheme 15) Purpose of check valve is to prevent liquid fuel from re-entering the fuel filler pipe during refueling or during a vehicle rollover condition.
2. Fuel Filler Pipe Flapper Valve The fuel filler pipe flapper valve on Escort SOHC and Tracer SOHC, is located inside fuel filler pipe. (Scheme 16) Purpose of flapper valve is to minimize fuel flow from backing up into fuel filler pipe. Flapper valve is not a positive seal to fuel tank.
3. Fill Limit Valve Assembly The fill limit valve assembly on Escort SOHC and Tracer SOHC controls fuel tank volume and prevents fuel from entering the vent tube in a vehicle rollover condition. The fill limit valve consists of a vent tube, vapor seal (which has an "O" ring on both ends) and a check valve which consists of a float with a spring assembly.
4. Fuel Vapor Vent Valve Fuel Vapor vent valve assembly is mounted on top of fuel tank and is used to control flow of fuel vapor entering the fuel tank vapor delivery line to the EVAP canister. The head valve portion of the fuel vapor vent valve prevents fuel tank from overfilling during refueling. The fuel vapor vent valve also has a spring supported float that prevents liquid fuel from entering fuel tank vapor delivery line under severe handling or a vehicle rollover condition.
5. Fuel Vapor Control Valve (Fuel Tank Mounted) The fuel vapor control valve on Crown Victoria, Grand Marquis, Sable 3.0L 2-Valve, Taurus 3.0L 2-Valve and Town Car is used for preventing liquid fuel from entering the EVAP canister and EVAP canister purge valve.
6. EVAP Canister Fuel Vapors from fuel tank are stored in EVAP canister. With engine running at a RPM higher than idle, vapors are purged from EVAP canister back into the engine for combustion.

Scheme 15

Scheme 16

POSITIVE CRANKCASE VENTILATION (PCV)

PCV system uses intake manifold vacuum to recycle blow-by vapors from the crankcase to the combustion chamber, where they are burned. PCV valve meters flow of blow-by vapors, according to manifold vacuum. When high amounts of blow-by gases are produced (such as worn piston rings), excess gases flow back through crankcase vent hose into the air inlet and are burned during normal combustion.

SELF-DIAGNOSTIC SYSTEM

Note. All systems have self-diagnostic capabilities. For information on procedures for entering self-test modes and reading Diagnostic Trouble Codes (DTCs), see TROUBLE SHOOTING - NO CODES - EEC-V article.

The MIL is located on the instrument cluster and is labeled CHECK ENGINE or SERVICE ENGINE SOON. MIL will illuminate when ignition switch is turned to the ON position (bulb check), or when systems related to the EEC-V system malfunction during normal engine operation. For additional information, see TROUBLE SHOOTING - NO CODES - EEC-V article.

See also:
• POWERTRAIN CONTROL MODULE LOCATION
• EGR SYSTEM
• SELF-DIAGNOSTIC SYSTEM