TERMINOLOGY
Due to Federal government requirements, manufacturers may use names and acronyms for systems and components different than those used in previous years. The following table will help eliminate confusion when dealing with these components and systems. Only relevant components and systems whose names have changed from current Ford Motor Co. terminology have been listed. See REVISED TERMINOLOGY table.
| 1992 & Earlier | 1993 & After |
|---|---|
| ACT | Air Intake Temperature (AIT) Sensor |
| BP SENSOR | Barometric Pressure (BARO) Sensor |
| CHECK ENGINE Light | Malfunction Indicator Light (MIL) |
| Camshaft Sensor | Camshaft Position (CMP) Sensor |
| CPS | Crankshaft Position (CKP) Sensor |
| DIS | Electronic Ignition (EI) Low Data |
| Rate System | |
| ECA | Powertrain Control Module (PCM) |
| EDIS | Electronic Ignition (EI) High Data |
| Rate System | |
| EGO | Oxygen Sensor (O2S) |
| ESA | Distributor Ignition |
| HEGO | Heated Oxygen Sensor (HO2S) |
| Inertia Switch | Inertia Fuel Shutoff (IFS) Switch |
| Intercooler | Charge Air Cooler (CAC) |
| NGS | Park/Neutral Position (PNP) Switch |
| PRCS | Fuel Pressure Regulator |
| Control (FPRC) Solenoid | |
| Self-Test Connector | Data Link Connector (DLC) |
| DIS Module, EDIS Module | |
| Or TFI-IV Module | Ignition Control Module (ICM) |
| Thermactor Air System | Secondary Air Injection (AIR) System |
| Thick Film Ignition-IV | Distributor Ignition (DI) |
| TPS | Throttle Position (TP) Sensor |
REVISED TERMINOLOGY
POWERTRAIN CONTROL MODULE (PCM)
During system operation, PCM transmits electrical reference signals to engine sensors and analyzes return signals to determine engine operating conditions. (Scheme 1) If a sensor, circuit or actuator fails, PCM initiates an alternative strategy, allowing vehicle to continue to be driven. This strategy is called Failure Mode Effects Management (FMEM).
The MIL light will glow and stay on whenever FMEM occurs. During FMEM, the PCM continues to monitor failed sensor/circuit. Should sensor/circuit signals return to normal, PCM will cancel FMEM and resume control based on sensor signals.
| Application | Location |
|---|---|
| Bronco | Behind Left Kick Panel |
PCM LOCATION
Scheme 1
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, covering components which control or produce voltage signals monitored by the PCM. The second category is OUTPUT SIGNALS, covering components controlled by the PCM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see WIRING DIAGRAMS in this article. The following input signals are available.
A/C Compressor Clutch Signal
When battery voltage is supplied to A/C compressor clutch, PCM receives a signal, which it uses to increase engine idle speed to compensate for A/C compressor load.
Air Intake Temperature (AIT) Sensor
The AIT sensor provides PCM with temperature mixture information. The AIT sensor is used both as a density corrector for airflow calculation and as cold enrichment fuel flow.
Barometric Pressure (BARO) Sensor
BARO sensor measures barometric pressure of atmosphere. Variations in atmospheric pressure (changes in altitude) modify an electrical signal monitored by PCM. The BARO sensor input affects spark advance, EGR flow and air/fuel mixture adjustments by PCM. Sensor input is updated during key-on and wide open throttle applications. BARO sensor looks identical to Manifold Absolute Pressure (MAP) sensor.
Note. Tubing nipple on BARO sensor is open to atmosphere, while tubing nipple on MAP sensor is connected to intake manifold.
Brake On-Off (BOO) Switch
The BOO switch is mounted on brake pedal. It detects deceleration for air/fuel ratio adjustment.
Clutch Engage Switch
This switch is mounted at clutch pedal and signals position of clutch pedal to PCM. Clutch engage switch signal to PCM affects air/fuel ratio and idle speed.
Coolant Temperature Sensor
See ENGINE COOLANT TEMPERATURE (ECT) SENSOR.
Crankshaft Position (CKP) Sensor
A dual Hall Effect crankshaft sensor, mounted at crankshaft pulley, is used on 2.3L dual-plug Electronic Ignition (EI) system. Sensor signals are generated when 2 trigger wheels, mounted on pulley assembly, pass through air gap of 2 Hall Effect switches. One switch produces a Profile Ignition Pick-up (PIP) signal, monitored by DIS ignition module to provide RPM signal to PCM. The second switch produces Cylinder Identification (CID) signal, used by EI ignition module to identify which coil pack to trigger. If CID signal is not present, vehicle will be hard to start.
EGR Valve Position (EVP) Sensor
Mounted on EGR valve, EVP sensor detects EGR valve position and transmits this information to PCM. The EVP signal affects EGR flow and ignition timing.
Engine Coolant Temperature (ECT) Sensor
Threaded into coolant passage near thermostat housing, ECT sensor inputs coolant temperature to PCM. The signal from ECT affects air/fuel ratio, idle speed, EGR flow, purge flow, fuel pressure, boost pressure (turbo engine) and ignition timing output signal from PCM.
Heated Oxygen Sensor (HO2S)
The HO2S is mounted in exhaust manifold. When at operating temperature, the HO2S monitors oxygen content of exhaust gases. A heating circuit is used to warm HO2S to operating temperature, enabling faster conversion of feedback system to closed loop operation.
The HO2S produces low voltage (less than .4 volt) to indicate a lean mixture (high amount of oxygen) or high voltage (more than .6 volt) to indicate a rich mixture (low amount of oxygen). This voltage signal is transmitted to PCM.
Manifold Absolute Pressure (MAP) Sensor
Manifold pressure and temperature are used by the PCM to calculate the airflow rate. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes.
The MAP sensor uses frequency to measure manifold vacuum. The MAP sensor is used as a barometric sensor for altitude compensation, updating the PCM during Key On, Engine Off (KOEO) and at Wide Open Throttle (WOT). By monitoring MAP sensor output voltage, the PCM can determine correct rate of spark advance, EGR flow and air/fuel ratio. If MAP sensor fails, the PCM will supply a fixed MAP value and use the Throttle Position (TP) sensor to control fuel distribution.
Mass Airflow (MAF) Sensor
MAF sensor measures flow of air entering the engine. This measurement of airflow is a reflection of engine load (throttle opening). The sensing element (hot wire) is a thin platinum wire wound on a ceramic bobbin and coated with glass. The hot wire is maintained at 392°F (200°C) above cold wire (ambient) temperature. Cold wire is located downstream of hot wire. As air passes through the airflow sensor, the air temperature is measured as air passes over the cold wire sensor. The PCM uses this information to control fuel delivery.
Park/Neutral Position (PNP) Switch
The PNP monitors in-gear conditions and sends signal to PCM. This signal affects air/fuel ratio, idle speed and ignition timing.
Neutral Safety Switch (NSS)
Mounted on side of transmission, this switch monitors gear position on automatic transmission vehicles. The signal affects air/fuel ratio, idle speed and EGR flow.
Power Steering Pressure (PSP) Switch
The PSP switch monitors power steering pressure and signals PCM to adjust engine idle speed under load conditions. Switch is located in high pressure line from PSP pump to steering rack assembly.
Profile Ignition Pick-Up (PIP)
On Distributor Ignition (DI) systems, PIP signal is provided by a 12-volt reference from ignition module to Hall Effect switch inside distributor. This reference voltage is modulated by window/shutter Hall Effect switch. Monitored reference is pulled low when shutter blade is out of Hall Effect switch window.
When shutter blade enters window, 12-volt reference returns, and ignition module sends PIP signal to PCM. PCM uses the PIP signal as an RPM reference to calculate timing adjustments. PCM timing control returns to ignition module in form of a Spark Output (SPOUT) signal.
Self-Test Output/Self-Test Input (STO/STI) Connectors
The STO connector is a 6-pin connector used to perform self-test diagnostic procedure. The STI is a single-pin connector, located next to STO. When STI is grounded, it activates fault code output function. Codes are retrieved through STO connector.
Throttle Position (TP) Sensor
Mounted on throttle body at throttle plate rod, TP sensor monitors throttle plate opening. The TP sensor signal to PCM is proportional to throttle opening angle. The TP sensor signal affects air/fuel ratio, injector timing, idle speed, EGR flow and fuel pressure. If TP sensor system malfunctions, Code 12 will be set in PCM memory.
Vehicle Speed Sensor (VSS)
The transmission-mounted VSS sends a pulsing signal to PCM when vehicle is moving. The VSS generates pulses with axle shaft revolution. The PCM interprets speed sensor input along with TP sensor closed throttle input.
This input enables PCM to differentiate between closed throttle deceleration and closed throttle idle (vehicle stopped) conditions. During deceleration, PCM controls Idle Air Control (IAC) valve to maintain a desired manifold pressure. During idle, PCM controls IAC motor to maintain a desired idle speed.
OUTPUT SIGNALS
Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on components, refer to indicated system.
A/C Clutch Cycling Switch
See MISCELLANEOUS CONTROLS.
Canister Purge Solenoid Valve
See EMISSION SYSTEMS.
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM.
Cooling Fan
See MISCELLANEOUS CONTROLS.
EGR System
See EMISSION SYSTEMS.
Fuel Injectors
See FUEL SYSTEMS.
Fuel Pump
See FUEL SYSTEMS.
Fuel Pressure Regulator
See FUEL SYSTEMS.
Idle Air Control (IAC) Valve
See FUEL SYSTEMS.
Self-Diagnostic
See SELF-DIAGNOSTIC SYSTEM.
Self-Test Output/Self-Test Input Connectors
See SELF-DIAGNOSTIC SYSTEM.
Wide Open Throttle A/C Cutoff
See MISCELLANEOUS CONTROLS.
System Types
Fuel delivery systems differ in design depending on model. System designs use one of the following configurations
- Single tank with single pump.
- Single tank with dual pump.
- Dual tank with mechanical selector valve/reservoir.
Low Pressure Fuel Pump
Some vehicles have a primary, low pressure in-tank pump for supplying fuel to reservoir. The low pressure pump rests in a sump (depression) in fuel tank. A nylon screen protects low pressure pump inlet from contaminating particles.
When dual tanks are used, each tank is equipped with a low pressure pump. Such a system has a total of 3 pumps: 2 low pressure and one high pressure.
High Pressure Fuel Pump
The high pressure fuel pump is positioned inside fuel tank. A reservoir is built onto pump and sender assembly.
In a 2-tank system, sender assembly handles switching of high pressure fuel through internal valves. Should one tank overfill during use (return line returns fuel to wrong tank), pump and sender unit in overfilling tank need replacement.
The high pressure fuel pump is capable of pumping over 33 gallons (125L) of fuel per hour at a working pressure of 39.2 psi (2.75 kg/cm 2 ). This pump also has internal pressure relief and discharge check valves.
Mechanical Selector Valve
A driver-operated selector switch controls selector valve for switching fuel supply from one tank to another. This valve switches fuel supply and return lines from one tank to another in response to fuel pressure from in-tank pumps acting on its actuating diaphragm.
The diaphragm switches tank connection when less than 2 psi of fuel pressure is acting on upper side of front tank and lower side of rear tank. Valve function depends upon proper operation of in-tank low pressure pumps. In all dual-tank vehicles, excess fuel not used by engine is returned to same tank from which it was pumped.
Reservoirs & Filters
Fuel reservoirs are used to prevent fuel flow interruptions during extreme vehicle maneuvers with low tank fill levels. Reservoir is molded into plastic fuel pump and sender housing.
The fuel pressure regulator is attached to fuel supply manifold assembly, downstream of fuel injectors. It regulates fuel pressure supplied to injectors. Regulator is a diaphragm-operated valve with one side responding to fuel pressure and the other side to intake manifold vacuum.
When intake manifold vacuum is low, an internal spring increases pressure on diaphragm, blocking off fuel return passage and increasing fuel pressure. When manifold pressure is high, spring pressure is overcome by vacuum, opening fuel return passage and lowering fuel pressure. Excess fuel is by-passed through regulator and returned to fuel tank.
Fuel Pump Actuation
When ignition switch is turned to START position, PCM operates fuel pump relay to provide fuel for starting engine. PCM senses engine speed and shuts off fuel pump by opening ground circuit to fuel pump relay when engine stops or speed drops to less than 120 RPM. When ignition switch is in ON position, EEC power relay is energized (contacts closed). Power is provided to fuel pump relay and timer in PCM. Fuel pump receives power through fuel pump relay contacts.
Inertia Fuel Shutoff (IFS) Switch
All models use an electrical interrupt switch in fuel system. During a collision or vehicle rollover, electrical contacts within inertia switch open, shutting off fuel supply to electric fuel pump. Fuel supply is interrupted even when engine is running.
A reset button is located on switch assembly. If electrical circuit trips, vehicle will not restart until switch is reset. Fuel system should be inspected before resetting switch.
On Bronco, IFS switch is located on left toe board, near parking brake assembly.
Note. After an accident, DO NOT reset IFS switch until entire fuel system has been inspected for leaks.
FUEL CONTROL
Precise fuel metering is accomplished with EEC-IV system. The PCM continually monitors engine operating conditions based on information received from various sensors and switches. In response to information received, PCM calculates optimum air/fuel mixture in relation to present engine operating conditions and affects required metering adjustments through output actuators control.
Fuel Injection
The PCM controls fuel injectors to meter pulse width or time each injector is energized. Each injector receives battery voltage through ignition switch circuit. The PCM-controlled ground circuit completes circuit to energize injector. The PCM receives inputs from engine sensors to compute fuel flow necessary to maintain air/fuel mixture ratio throughout entire engine operational range.
Each cylinder has a solenoid-operated injector which sprays fuel toward back of each intake valve. Injector bodies consist of solenoid-actuated pintle and needle valve assembly.
The IAC valve, mounted on the throttle body, controls idle speed by regulating throttle plate by-pass air. IAC valve includes an air by-pass valve and idle speed control solenoid valve. The air by-pass valve is affected by the engine coolant temperature and functions during cold engine conditions less than 122°F (50°C). The idle speed control solenoid is controlled by PCM and works throughout the entire temperature range.
On some models, idle is controlled by idle speed control air by-pass valve. A throttle air by-pass valve is a solenoid-operated valve controlled by PCM. The valve allows air to by-pass throttle plates to control cold engine fast idle, no-touch start, dashpot, overtemperature idle boost and engine load idle correction.
Air by-pass channel carries idle airflow regulated by air by-pass valve. Air by-pass valve is controlled by PCM to adjust both cold and warm idle speeds. Air by-pass valve uses solenoid valve to vary idle airflow volume allowed to enter engine.
Distributor Ignition (DI)
All engines, except those with distributorless ignition systems, use DI systems. The DI distributor is a gear-driven, die-cast unit. A Hall Effect stator assembly is used to trigger ignition coil. This distributor does not use conventional centrifugal/vacuum advance mechanisms. The DI module is mounted on cowl behind engine.
The DI distributor uses a Hall Effect switch mechanism to switch primary voltage and send a Profile Ignition Pick-Up (PIP) signal to PCM. The PCM uses PIP input signal to produce a Spark Output (SPOUT) signal, which is sent to DI module to trigger coil secondary voltage discharge.
On manual transaxle vehicles, the DI ignition module features a push-start mode, which allows vehicle to be push-started if necessary. An "E" core ignition coil is used.
EMISSION SYSTEMS
Several systems and components are used to control emissions. Operation and actuation method is provided for most devices. For testing procedures, refer to specific system in the article I - SYSTEM/COMPONENT TESTS in the ENGINE PERFORMANCE section.
Temperature Vacuum Switch (TVS)
The TVS incorporates a bimetallic disc which opens and closes vacuum ports. TVS may be used in conjunction with distributor, canister purge or EGR systems.
Vacuum Control Valve
This temperature-operated vacuum switch has 2 or more ports. Valve uses a wax pellet or bimetallic material to open or close vacuum ports at normal engine operating temperatures.
Vacuum control valve is usually mounted in some part of cooling system with its base immersed in coolant. Valve may be either normally open or closed.
Vacuum Delay Valve
Vacuum delay valve is inserted in vacuum lines to provide gradual application or vacuum release to engine or emission control devices. One-way or two-way valve may be used, depending on function and system.
Vacuum Reservoir
The vacuum reservoir stores vacuum and provides an amplified vacuum signal, preventing rapid fluctuations or sudden drops in a vacuum signal during such conditions as acceleration.
Vacuum Restrictor
This orifice-type flow restrictor is used as an emission calibration to control flow rate and/or actuation timing of components and systems.
Vacuum Vent Valve
Vacuum vent valve controls induction of fresh air into system, preventing accumulation of fuel vapors which could cause decay of vacuum diaphragms. Valve may be vent only or combined vent and delay valve. Valve should always be mounted with ports pointing downward.
AIR INJECTION SYSTEM
The air injection system reduces carbon monoxide (CO) and hydrocarbon (HC) content of exhaust gases. It injects fresh air into exhaust gas stream, which continues combustion of unburned gases. Air can be by-passed to atmosphere by a thermactor air by-pass valve and/or directed near exhaust manifold or catalytic converter.
Depending upon engine size and application, individual systems may vary in number and type of components. All systems use same basic components: air supply pump, air by-pass valve, filter, check valve(s), air control valve, air manifold and air hoses. Some models may use a combined air by-pass/air control valve.
Air By-Pass Valve
Valve directs airflow from thermactor air pump to exhaust system or atmosphere as required. Valve may be mounted on air pump or in-line (remote). Air by-pass valve is vacuum operated and may be either normally open or closed.
Normally closed valve supplies air to exhaust system with medium and high applied vacuum signals during normal modes, short idles and some acceleration. With low or no vacuum applied, pump air is dumped through silencer valve ports.
Normally open valve with a vacuum vent provides a timed air dump during deceleration. Valve also dumps when a vacuum pressure difference is maintained between signal and vent ports.
Air Pump
The air pump is a belt-driven, positive displacement, vane-type pump which provides air for air injection system. Air is received from a remote silencer/filter, attached to air inlet nipple of pump, or through a centrifugal fan on front of pump. The by-pass valve performs pressure relief.
The air pump supplies air under pressure to exhaust port near exhaust valve by either an external air manifold or through an internal drilled passage in cylinder head or exhaust manifold. This pressurized air, combined with hot exhaust gases, creates a secondary combustion stage, which produces carbon dioxide and water.
Air Supply Control Valve
Operated by vacuum, this valve directs air pump output upstream to exhaust manifold or downstream to catalytic converter.
Check Valves
Check valves are used on all thermactor systems in various locations. These valves allow airflow in one direction only.
Combination Air By-Pass & Air Control Valve
By-pass valve routes thermactor air to either the exhaust system or atmosphere. When air is routed to exhaust system, control valve routes air either upstream to exhaust manifolds or downstream to catalytic converter.
Both valves are normally closed and come in either a bleed or non-bleed type. Bleed-type valves will have bleed percentage molded into plastic case.
Dual Thermactor Air Control Solenoid Valve
The dual thermactor air control solenoid valve assembly consists of 2 normally closed solenoid valves with vents. One valve controls thermactor air by-pass valve and other controls thermactor air diverter valve. Both valves pass air when deactivated and do not pass air when activated.
Thermactor Idle Vacuum (TIV) Valve
The TIV valve vents vacuum signal to atmosphere when preset manifold vacuum or pressure is exceeded. During periods of extended idle, this valve is used to divert thermactor airflow to limit exhaust temperature. This prevents excessive underbody temperature. TIV valve also cuts EGR in a heavy boost mode for turbocharged applications.
Note. Not all vehicles use EGR systems. EGR system usage depends on engine application.
The Exhaust Gas Recirculation (EGR) system distributes exhaust gas into intake mixture. This lowers combustion temperatures due to lower concentrations of oxygen. Lowering combustion temperatures reduces NOx emissions.
Electronic EGR Valve
The Electronic EGR valve is required in EEC systems where EGR flow is controlled according to computer demands of EGR Valve Position (EVP) sensor. The EGR valve is operated by a vacuum signal from EGR Vacuum Regulator (EVR).
EGR valve is mounted on top of an intake and exhaust gas port. The EGR pintle blocks exhaust gas from entering intake system. When vacuum is applied to EGR valve, the diaphragm is actuated. This lifts EGR pintle (attached to diaphragm) and allows exhaust gas to recirculate into intake system.
EGR Vacuum Regulator (EVR)
The vacuum regulator is an electromagnetic device controlling vacuum to EGR valve. Regulator operation is measured as a duty cycle: increased duty means increased vacuum to EGR.
This sensor is attached to EGR valve assembly and indicates EGR valve position to PCM.
EVAPORATIVE EMISSION CONTROL
Note. Not all listed components are used on every vehicle system. Component usage depends on calibration of vehicle.
The function of evaporative emission control system is to store gasoline fumes from fuel system in a carbon canister when engine is not running. During engine operation, fumes are drawn into engine for burning during combustion process, purging canister.
Three basic components are used in evaporative emission system
- Activated carbon canister.
- Computer-controlled solenoid.
- Tank pressure control cap.
For specific component application and vacuum hose routing, see M - VACUUM DIAGRAMS article in the ENGINE PERFORMANCE section.
Carbon Canister
Carbon canister storage is used for evaporative fuel control on all vehicles.
This normally closed solenoid valve controls fuel vapor flow from canister to intake manifold. It is opened or closed by a signal from PCM during various engine operating modes.
Fill Control/Vent System
Fill limiting is accomplished through configuration of fill neck and/or internal vent lines. Vent system is designed to permit air space in 10-12 percent of tank to allow for thermal expansion.
Vapor generated in fuel supply line is continuously vented back to fuel tank. Venting prevents engine surging from fuel enrichment and assists in hydrocarbon (HC) emission control.
Pressure/Vacuum Relief Fuel Cap
This system consists of a sealed filler cap with an integral pressure/vacuum relief valve. Fuel system vacuum relief is provided after one in. Hg. Pressure relief is provided after 1.8 psi (.13 kg/cm 2 ). Under normal conditions, filler cap allows air to enter fuel tank as fuel is used, without allowing fuel vapors to escape.
Vapor Vent System
System provides a vapor space above gasoline surface in fuel tank. This area is sufficient to permit adequate breathing room for tank vapor valve assembly.
All vapor valves are mounted on fuel tank and use a small orifice which allows vapor (but not liquid) fuel to pass into line running to canister. Fuel vapors in fuel tank are vented though vapor valve assembly on top of fuel tank. Vapors are routed through a vapor line to carbon canister in engine compartment.
POSITIVE CRANKCASE VENTILATION (PCV)
The PCV system uses intake manifold vacuum to eliminate blow-by gases from crankcase. Manifold vacuum draws gases from crankcase, through PCV hose, into combustion chamber. The PCV valve is positioned in hose through which blow-by gases flow on their way to combustion chamber.
By opening and closing in direct relation to engine vacuum, the PCV valve meters blow-by gas flow to combustion chamber. During periods of high manifold vacuum, such as at idle and deceleration, valve is almost completely closed, limiting flow of gases. During cruise speeds, valve permits greatest flow of gases.
Under conditions in which excessively high amounts of blow-by gases are produced (such as worn cylinders or rings), system allows excess gases to flow back through crankcase vent hose and into intake manifold.
The MIL (if equipped) will illuminate whenever ignition is turned to ON position (bulb check) or systems related to the EEC-IV system malfunction during normal engine operation. For additional information, see G - TESTS W/CODES - EEC-IV article in the ENGINE PERFORMANCE section.
A/C CLUTCH CYCLING PRESSURE SWITCH (CCPS)
On models with manual A/C system, the CCPS is mounted on top of the receiver-drier. Based on refrigerant system pressure, a signal is sent to the PCM. The PCM uses this signal to maintain system pressure within the programmed range.
The PCM regulates operation of the electric cooling fan through a PCM-controlled relay, which controls the ground or power circuit of the cooling fan. This allows the PCM to operate the cooling fan based on engine temperature. A malfunction of the cooling fan will cause engine overheating and possible detonation.
WIDE OPEN THROTTLE A/C (WAC) CUTOFF
During wide open throttle, WAC circuit interrupts power to A/C compressor clutch. The A/C remains off for about 3 seconds after returning from WAC.
