ENGINE CONTROLS - THEORY & OPERATION - 5.0L

• HEADINGS
  • INTRODUCTION
  • COMPUTERIZED ENGINE CONTROLS
    • CONTROLS
      • Powertrain Control Module (PCM)
      • Constant Control Relay Module (CCRM)
      • Fuel Pump Driver Module (FPDM)
    • INPUT DEVICES
      • Brake On/Off (BOO) Switch
      • Camshaft Position (CMP) Sensor
      • Clutch Pedal Position (CPP) Switch
      • Coolant Temperature Sensor
      • Crankshaft Position (CKP) Sensor
      • Cylinder Head Temperature (CHT) Sensor
      • Data Link Connector (DLC)
      • Differential Pressure Feedback EGR (DPFE) Sensor
      • Electronic Vacuum Regulator (EVR) Solenoid
      • Engine Coolant Temperature (ECT) Sensor
      • Engine RPM / Vehicle Speed Limiter System
      • Fuel Pump Monitor (FPM)
      • Heated Oxygen Sensor (HO2S)
      • Mass Airflow (MAF) Sensor
      • Octane Adjust Shorting Bar
      • Output Shaft Speed (OSS) Sensor
      • Park/Neutral Position (PNP) Switch
      • Throttle Position (TP) Sensor
      • Transmission Control Switch (TCS)
      • Transmission Fluid Temperature (TFT) Sensor
      • Vehicle Speed Sensor (VSS)
    • OUTPUT SIGNALS
      • A/C Cycle Switch (ACCS)
      • A/C Pressure Switch (ACPSW)
      • By-Pass Air (BPA) Valve
      • Canister Purge Valve
      • Canister Purge Solenoid Valve
      • EGR System
      • Fuel Injectors
      • Fuel Pump
      • Fuel Pressure Regulator
      • Idle Air Control (IAC) Solenoid
      • Inertia Fuel Shutoff (IFS) Switch
      • Malfunction Indicator Light
      • Transmission Solenoids
  • FUEL SYSTEM
    • FUEL DELIVERY
      • Fuel Pump
      • Fuel Pressure Regulator
      • Inertia Fuel Shutoff (IFS) Switch
    • FUEL CONTROL
      • Fuel Injectors
    • IDLE SPEED
      • Idle Air Control (IAC) Valve Assembly
  • IGNITION SYSTEM
    • ELECTRONIC IGNITION (EI) (HIGH DATA RATE) SYSTEM
  • EMISSION SYSTEMS
    • SYSTEMS
      • Temperature Vacuum Switch (TVS)
      • Vacuum Control Switches
      • Vacuum Reservoir
      • Vacuum Restrictor
      • Vacuum Vent Valves
    • AIR INJECTION SYSTEM
      • Electronic Secondary Air Injection (EAIR) System
    • EGR SYSTEM
      • EGR Valve
      • Differential Pressure Feedback Electronic (DPFE) Sensor
      • Electronic Vacuum Regulator (EVR) Solenoid
    • FUEL EVAPORATIVE SYSTEM
      • Carbon Canister
      • Canister Purge (CANP) Solenoid Valve
      • Fill Control/Vent System
      • Pressure/Vacuum Relief Fuel Cap
      • Rollover/Vent Valve
      • Vapor Vent System
    • POSITIVE CRANKCASE VENTILATION (PCV)
  • SELF-DIAGNOSTIC SYSTEM
    • MALFUNCTION INDICATOR LIGHT (MIL)
  • MISCELLANEOUS CONTROLS
    • A/C
      • A/C Cycle Switch (ACCS)
      • A/C Pressure Switch (ACPSW)
    • TRANSMISSION
      • Solenoids
• FIGURES
  • Fig. 1: Locating HO2S
  • Fig. 2: Cross-Sectional View Of MAF Sensor
  • Fig. 3: Identifying Fuel Pump Components
  • Fig. 4: Cross-Sectional View Of Pressure Regulator Components
  • Fig. 5: Identifying IFS Reset Button Switch Positions
  • Fig. 6: Cross-Sectional View Of IAC Valve Assembly Components
  • Fig. 7: EGR System Schematic
• TABLES

E - THEORY/OPERATION - 5.0L

1996 ENGINE PERFORMANCE Ford Motor Co. - Theory & Operation - EEC-V

INTRODUCTION

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.

COMPUTERIZED ENGINE CONTROLS

CONTROLS

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. PCM is located behind right kick panel.

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.

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.

Fuel Pump Driver Module (FPDM)

FPDM interfaces with the PCM to control fuel pump operation. By controlling fuel pump operation, noise and the amount of hot fuel returned to the fuel tank is minimized. If FPDM or system fail self-test, DTC P1230, P1233, P1234, P1235 P1236, P1237 or P1238 may be set in PCM memory.

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.

INPUT DEVICES

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 diagram in the WIRING DIAGRAMS - 5.0L article. The available input signals include the following:

Brake On/Off (BOO) Switch

BOO switch is wired to brakelight circuit. It signals the PCM when the brake is applied. The BOO 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 variable reluctance sensor is used.

CMP sensor is used to determine the position of the camshaft and to identify when piston No. 1 is at TDC of compression stroke. CMP sensor provides cylinder identification information during engine start-up for PCM to initiate correct firing order. Cylinder identification information signal is sent from CMP sensor to PCM through CID circuit.

Clutch Pedal Position (CPP) Switch

CPP switch is mounted near clutch pedal. CPP 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.

Coolant Temperature Sensor

See ENGINE COOLANT TEMPERATURE (ECT) SENSOR (Below).

Crankshaft Position (CKP) Sensor

CKP sensor is a Hall Effect magnetic switch. The Hall Effect switch is activated by vanes on the crankshaft damper and pulley assembly. The Profile Ignition Pick-Up (PIP) is a crankshaft position signal that is sent to the PCM. The PIP signal generated by the Hall Effect sensor provides base timing and RPM information to the PCM.

Cylinder Head Temperature (CHT) Sensor

CHT sensor is the input signal used for the cooling system failsafe strategy. CHT sensor signals PCM to activate failsafe strategy if cylinder head temperature exceeds pre-programmed conditions. If CHT sensor or system fail self-test, DTC P1288, P1289, P1290 or P1299 may set in PCM memory.

Data Link Connector (DLC)

The 16-pin Data Link Connector (DLC) is used to perform the Quick Test diagnostic procedure. When scan tool connected to DLC, fault code output function can be activated.

Differential Pressure Feedback EGR (DPFE) Sensor

See EGR SYSTEM under EMISSION SYSTEMS.

Electronic Vacuum Regulator (EVR) Solenoid

See EGR SYSTEM under EMISSION SYSTEMS.

Engine Coolant Temperature (ECT) Sensor

ECT sensor is a thermistor device 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 RPM / Vehicle Speed Limiter System

The engine RPM/vehicle speed limiter system is integrated into PCM. The purpose of this system is to prevent damage to the powertrain in overspeed conditions.

Whenever engine RPM or vehicle speed is detected, PCM will disable some or all of the fuel injectors. This will cause engine to run rough and DTC P1270 will set in PCM memory. When overspeed condition has been discontinued, normal engine operating conditions will be restored.

Fuel Pump Monitor (FPM)

FPM circuit is spliced into the Power-To-Pump 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 the fuel pump off and the FPM circuit low, the PCM can verify that FPM and, circuit and Power-To-Pump circuit are complete from the FPM splice through the fuel pump to ground.

With the fuel pump on, voltage is supplied from the CCRM to the Power-To-Pump and FPM circuits. With the fuel pump on and FPM circuit high, PCM can verify that Power-To-Pump circuit from CCRM to FPM splice is complete. It can also verify that fuel pump relay contacts are closed and battery voltage is supplied to CCRM for the relay. See CCRM circuit schematic in CIRCUIT TEST X in the TESTS W/CODES - 5.0L article for more information.

Heated Oxygen Sensor (HO2S)

The heated oxygen sensors are mounted in the exhaust manifold and pipe. See Fig. 1 . 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.

Fig. 1: Locating HO2S
Courtesy of FORD MOTOR CO.

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) above ambient temperature, as measure by a constant cold wire. See Fig. 2 .

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

Fig. 2: Cross-Sectional View Of MAF Sensor
Courtesy of FORD MOTOR CO.

Octane Adjust Shorting Bar

The octane adjust shorting bar is used to retard spark. A diagnostic trouble code will set if Octane Adjust Shorting Bar is removed or, if an open circuit is present.

Output Shaft Speed (OSS) Sensor

The OSS sensor is a magnetic pick-up that sends a voltage signal to the PCM. This signal tells the PCM transmission output shaft speed. Voltage is also used for shift schedules, modulated converter clutch control, and determining EPC pressure.

OSS sensor is located on the rear of transmission case, on driver's side of vehicle. Control functions associated with OSS sensor are limiting vehicle speed, converter clutch control and shift quality.

Park/Neutral Position (PNP) Switch

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

Throttle Position (TP) Sensor

TP sensor is a rotary potentiometer. TP sensor monitors throttle plate opening. Its 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, at throttle plate rod.

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 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 below are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

A/C Cycle Switch (ACCS)

See MISCELLANEOUS CONTROLS .

A/C Pressure Switch (ACPSW)

See MISCELLANEOUS CONTROLS .

By-Pass Air (BPA) Valve

See IDLE SPEED under FUEL SYSTEM .

Canister Purge Valve

See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS .

Canister Purge Solenoid Valve

See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS .

EGR System

See EGR SYSTEM under EMISSION SYSTEMS .

Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM .

Fuel Pump

See FUEL DELIVERY under FUEL SYSTEM .

Fuel Pressure Regulator

See FUEL DELIVERY under FUEL SYSTEM .

Idle Air Control (IAC) Solenoid

See IDLE SPEED under FUEL SYSTEM .

Inertia Fuel Shutoff (IFS) Switch

See FUEL DELIVERY under FUEL SYSTEM .

Malfunction Indicator Light

See SELF-DIAGNOSTIC SYSTEM .

Transmission Solenoids

See MISCELLANEOUS CONTROLS .

FUEL SYSTEM

NOTE:

For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article.

FUEL DELIVERY

Fuel Pump

Fuel is supplied by an in-tank electric fuel pump. Pump also has a discharge check valve to maintain system pressure during shutdowns and to minimize starting problems. See Fig. 3 .

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. Constant fuel pressure is maintained to injector nozzles by fuel pressure regulator.

Fig. 3: Identifying Fuel Pump Components
Courtesy of FORD MOTOR CO.

Fuel Pressure Regulator

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. See Fig. 4 .

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.

Fig. 4: Cross-Sectional View Of Pressure Regulator Components
Courtesy of FORD MOTOR CO.

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 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 the switch assembly. See Fig. 5 .

WARNING:

DO NOT reset IFS switch until complete fuel system has been inspected for leaks.

Fig. 5: Identifying IFS Reset Button Switch Positions
Courtesy of FORD MOTOR CO.

FUEL CONTROL

Fuel Injectors

The PCM controls fuel injector 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. This period is known as pulse width. Atomized spray pattern is obtained by shape of pintle.

IDLE SPEED

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. See Fig. 6 .

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.

Fig. 6: Cross-Sectional View Of IAC Valve Assembly Components
Courtesy of FORD MOTOR CO.

IGNITION SYSTEM

ELECTRONIC IGNITION (EI) (HIGH DATA RATE) SYSTEM

The EI (high data rate) system consists of a Crankshaft Position (CKP) sensor, Ignition Control Module (ICM) and either one 4-tower coil pack; one 6-tower coil pack; or two 4-tower coil packs.

The EI system operates by sending crankshaft position information from CKP sensor to ICM. The ICM generates a Profile Ignition Pick-Up (PIP) signal and sends it to the PCM.

The PCM responds with a Spark Output (SPOUT) signal containing advance or retard timing information back to the ICM. The ICM processes the CKP and SPOUT signals and decides which coils to fire. Also, the ICM generates an Ignition Diagnostic Monitor (IDM) signal to PCM, which is used to provide a tach output signal and indicate a failure mode if detected.

The CKP sensor is an electromagnetic device that senses movement of a 35 tooth wheel, located behind the crankshaft pulley. Each tooth is positioned in 10 degree increments with an empty slot (missing tooth) located BTDC. The detection of the missing tooth is what enables the PCM to identify crankshaft position and initiate correct firing order.

The ICM is a microprocessor with coil drivers. ICM strategy controls spark timing and coil firing. The ICM turns coils on and off at the correct time and in proper sequence, based on information from CKP sensor and a pulse width modulated signal (SPOUT) generated from PCM. The ICM receives CKP sensor and SPOUT signals and produces PIP and IDM output signals, which are sent to PCM.

The PCM receives ignition ground and PIP signals from the ICM, and then generates a SPOUT output signal based on engine speed, load, temperature and other sensor information. An IDM signal is received from ICM to determine if an ignition failure mode should be recorded.

The coil is turned on (coil charging) by ICM, and then turned off, firing 2 spark plugs at once. One plug is fired on the compression stroke; the other plug fires the mating cylinder, which is on the exhaust stroke. On the next cycle, firing strategy is reversed.

EMISSION SYSTEMS

Several systems and components are used to control emissions. Operation and method of actuation is provided for most devices. For specific testing procedures, refer to specific system in the TESTS W/CODES - 5.0L article.

SYSTEMS

Temperature Vacuum Switch (TVS)

TVS incorporates a bimetallic disc to open or close vacuum ports based on engine temperature.

Vacuum Control Switches

Temperature-operated vacuum switches have 2 or more ports. They utilize wax pellet or bimetallic material to either open or close the vacuum ports in conjunction with engine temperature.

Switches are normally mounted in some part of cooling system so the base is immersed in coolant. Switches may be normally open or normally closed. One version includes an electrical vacuum switch.

Vacuum Reservoir

Vacuum reservoir stores vacuum and provides an amplified vacuum signal. It prevents rapid fluctuations or sudden drops in a vacuum signal, such as during acceleration.

Vacuum Restrictor

This orifice-type flow restrictor is used in several emission calibrations to control the flow rate and/or actuation timing of components and systems.

Vacuum Vent Valves

Valves control induction of fresh air into system to prevent accumulation of fuel vapors, which could cause decay of vacuum diaphragms. Valve may be vent valve only or combination vent and delay valve. Valves should always be mounted so ports point 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.

Electronic Secondary Air Injection (EAIR) System

EAIR system consists of an electric air supply pump, Air Injection By-Pass (AIRB) solenoid and solid state relay. In the EAIR system, air can be by-passed to the atmosphere by AIRB solenoid, directed to exhaust manifold or catalytic converter.

EAIR system is monitored on primary and secondary side of solid state relay. Self-test is performed to confirm input from CKP, ECT, IAT sensor and HO2S. EAIR system must pass self-test before secondary air injection can be enabled. If EAIR system failure is detected in self-test, DTC P0411, P0412, P1413 or P1414 may set in PCM memory.

EGR SYSTEM

NOTE:

The self-diagnostic system monitors EGR performance and sets a trouble code if self-test requirements are not obtained.

EGR Valve

EGR valve is vacuum operated. The EGR valve is operated by a vacuum signal from EVR solenoid. Valve should be closed at 1.6 in. Hg and fully open at 4.5 in. Hg.

Differential Pressure Feedback Electronic (DPFE) Sensor

DPFE sensor is a capacitive type pressure transducer that monitors the pressure difference across a metering orifice, located inside sensor. The DPFE 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 EVR duty cycle and achieve the desired EGR flow. See Fig. 7 .

Electronic Vacuum Regulator (EVR) Solenoid

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

Fig. 7: EGR System Schematic
Courtesy of FORD MOTOR CO.

FUEL EVAPORATIVE SYSTEM

Carbon Canister

Carbon canister storage is used for evaporative emission control on all vehicles. The function of evaporative emission control systems is to store gasoline fumes from fuel tank in a carbon canister until fumes can be drawn into engine for burning during combustion process.

Canister Purge (CANP) Solenoid Valve

Normally closed solenoid valve controls the flow of fuel vapors from canister to intake manifold. When engine is shut off, vapors from fuel tank flow into canister. After engine is started, CANP solenoid regulates fuel vapor flow by means of manifold vacuum and duty cycle signal from PCM.

Fill Control/Vent System

Fill limiting is accomplished through configuration of fuel filler neck and/or internal vent lines within fuel filler neck and tank. Vent system is designed to permit air space in 10-12 percent of tank when tank is filled to capacity. Air space provides for thermal expansion of fuel and also aids in-tank vapor vent system.

Pressure/Vacuum Relief Fuel Cap

This system consists of a sealed filler cap with an integral pressure/vacuum relief valve. Under normal conditions, filler cap allows air to enter fuel tank as fuel is used, while preventing vapors from escaping.

Rollover/Vent Valve

Rollover/vent valve is located on highest point of fuel tank. With fuel in the fuel tank, pressure increases, and the rollover/vent valve releases this extra pressure into the atmosphere. Also, if vehicle is in a rollover situation, the rollover vent valve closes and will not permit fuel or fuel vapors to escape from the fuel tank.

Vapor Vent System

System provides a vapor space above gasoline surface in fuel tank. Vapor space prevents liquid fuel from passing to the carbon canister.

Fuel vapors trapped in sealed fuel tank are vented though vapor valve assembly on top of fuel tank. Vapors are routed through a single vapor line to carbon canister in engine compartment. Vapors are stored in carbon canister until they are purged into engine during operation.

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 service codes, see TESTS W/CODES - 5.0L article.

MALFUNCTION INDICATOR LIGHT (MIL)

The 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 TESTS W/CODES - 5.0L article.

MISCELLANEOUS CONTROLS

NOTE:

Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

A/C

A/C Cycle Switch (ACCS)

The ACCS is a voltage input to the PCM which indicates when A/C is requested. When A/C demand switch is turned on, the cyclic pressure switch and the high pressure contacts of the dual function A/C Pressure Switch (ACPSW) are closed and voltage supplied to the ACCS circuit signal at the PCM. See CCRM circuit schematic in CIRCUIT TEST X in TESTS W/CODES - 5.0L article for more information.

A/C Pressure Switch (ACPSW)

The ACPSW is used for additional A/C system pressure control. The ACPSW is also referred to as the refrigerant containment/fan function switch. The normally open medium pressure contacts close at a predetermined A/C head pressure. This grounds the ACPSW circuit input to the PCM. The PCM will turn on high speed fan to help reduce pressure.

TRANSMISSION

Solenoids

The AODE transmission uses solenoids to shift transmission gear ratios, connect turbine and impeller inside torque converter and provide coasting on deceleration. Ground signal is controlled by PCM. Power is supplied to solenoids from the power relay.

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