Engine Controls - Theory & Operation - Eec 2.5L: Other Ford Probe II

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 previous Ford Motor Co. terminology have been listed. See REVISED TERMINOLOGY table.

REVISED TERMINOLOGY

Variable Resonance Induction System (VRIS)

VRIS opens and closes 3 shutter valves according to engine speed and throttle opening. VRIS shutter valves are located within the intake manifold. (Scheme 4) Two VRIS solenoids are operated by output signals from Powertrain Control Module (PCM). When solenoids are activated, vacuum is applied to the shutter valve actuators, which operate the shutter valves. Two vacuum chambers, located underneath left bank of intake manifold, maintain a constant vacuum supply to the VRIS shutter valve actuators during Wide Open Throttle (WOT) and other low-vacuum, low-speed conditions. The result is improved fuel efficiency and engine torque.

Scheme 4

CONTROL UNIT

The Powertrain Control Module (PCM) is the central computer which receives data from numerous sensors, switches and relays. The PCM processes information received and then generates output signals to control various relays, solenoids and actuators. The PCM has failure detection and self-diagnostic capability.

PCM is located in the center console below instrument panel.

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, which are components controlled by the control unit.

Barometric Pressure (BARO) Sensor

BARO measures barometric pressure of atmosphere. The PCM will adjust air/fuel ratio, A/C cutoff, idle speed, and purge control to compensate for changing pressure. Sensor is located inside PCM and cannot be serviced separately.

Brake On/Off (BOO) Switch

BOO switch is mounted on the brake pedal. It signals deceleration to PCM for air/fuel ratio adjustment.

Clutch Pedal Position (CPP) Switch

CPP switch is mounted at top of clutch pedal. Input signal from CPP is used by the PCM.

Coolant Temperature Sensor

See ENGINE COOLANT TEMPERATURE (ECT) SENSOR.

Camshaft Position (CMP) Sensor

The CMP is located in the distributor and detects cylinder No. 1 signal to be sent to PCM.

Crankshaft Position (CKP) Sensor

The PCM uses CKP input to determine injector and spark timing.

2 CKP sensors are used. CKP 1 sensor is located within the distributor and is used during engine starting and back-up if CKP 2 fails. CKP 2 sensor is mounted below the crankshaft pulley and is the primary crankshaft signal once engine is running. CKP 1 is a 6-vane rotor mounted to distributor shaft and spins at camshaft speed. As the rotor passes through a magnetic Hall Effect switch, the PCM calculates crankshaft position.

CKP 2 is mounted below crankshaft pulley, the sensor signal is generated directly from crankshaft rotation. This signal is used by the PCM for fuel injection timing, ignition timing, idle speed control and engine speed signal.

Data Link Connector (DLC)

The Data Link Connector (DLC) is used to perform the Quick Test diagnostic procedure. The DLC is located behind battery. When the PCM STI terminal of the DLC is connected to ground, fault code output function is activated.

EGR Valve Position (EVP) Sensor

EVP sensor detects EGR valve position and transmits information to the PCM. Sensor is mounted on top of EGR valve. The EVP signal affects EGR flow and ignition timing.

Engine Coolant Temperature (ECT) Sensor

Sensor signals coolant temperature to PCM. The ECT sensor changes resistance in response to coolant temperature. The ECT sensor resistance decreases as coolant temperature increases. The PCM uses ECT sensor signal to adjust ignition timing, EGR flow (2.5L), air/fuel ratio, idle speed and cooling fan operation.

Heated Oxygen Sensor (HO2S)

HO2S monitors oxygen content of exhaust gases. This electrically heated O2 sensor is mounted in the exhaust manifold or pipe. 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.

HO2S uses a built-in heating circuit. The heating circuit is used to bring the HO2S up to operating temperature, enabling faster conversion to closed-loop operation. The 2.5L is equipped with 2 sensors, one for each exhaust bank.

Idle Switch

The idle switch detects when throttle is closed and sends signal to PCM, indicating idle conditions are present. Idle switch is integrated into the throttle position sensor. PCM uses this signal to adjust air/fuel ratio and idle speed.

Intake Air Temperature (IAT) Sensor

IAT sensor is mounted in the airflow meter. Sensor monitors temperature of incoming air and sends signal to PCM. The PCM uses this signal to adjust air/fuel ratio.

Knock Sensor (2.5L)

The knock sensor detects vibrations (pre-ignition) and converts them into a voltage signal. The PCM monitors signal from KS and adjusts ignition timing if pre-ignition occurs. The knock sensor is threaded into the engine block, near the oil pressure switch.

Manual Lever Position (MLP) Switch

The MLP switch is used on vehicles with A/T. MLP switch monitors shift lever positions and then inputs signal to the PCM and Transaxle Control Module (TCM). This signal affects starter engagement, air/fuel ratio, idle speed and ignition timing.

Oxygen Sensor (O2S)

Voltage signal produced by the O2S indicates oxygen content of engine exhaust gases. O2S sensor is threaded into exhaust manifold. The PCM uses the O2S signal to regulate fuel injectors for proper air/fuel mixture.

Park/Neutral Position (PNP) Switch

PNP switch is used on M/T models only. The PNP switch monitors in-gear conditions and then inputs signal to the PCM.

Power Steering Pressure (PSP) Switch

The PSP switch monitors power steering pressure. When power steering fluid pressure exceeds the preset limit, the PSP switch sends an input signal to the PCM. The PCM then adjusts idle speed. PSP switch is located in power steering pump.

Throttle Position (TP) Sensor

TP sensor monitors throttle plate opening. Its signal to PCM is proportional to opening angle. TP sensor is mounted on throttle body, at throttle plate shaft.

Transmission Oil Temperature (TOT) Sensor

TOT 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 PCM. PCM uses this input signal to determine transmission fluid temperature.

Volume Airflow Meter (VAF)

The VAF is mounted in the air inlet, between air cleaner and throttle body. It measures the volume of air entering into the engine by monitoring the position of a movable door. A potentiometer, attached to VAF door, signals door position to the PCM. The PCM translates door position to volume of air entering the engine.

The VAF also contains an air temperature sensor. The temperature of air entering the engine is monitored and transmitted to the PCM. The PCM is programmed to compute airflow and air temperature, so fuel flow can be adjusted to obtain optimum air/fuel mixture. The VAF also contains a fuel pump switching circuit to cut fuel pump operation when the engine is off.

Vehicle Speed Sensor (VSS)

Sensor is transaxle mounted. VSS turns a Hall Effect sensor, which sends a constant pulse signal to PCM when vehicle is in motion.

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 of each output component, refer to the system indicated after component.

A/C Relay

See MISCELLANEOUS CONTROLS.

Canister Purge (CANP) Solenoid Valve

See EVAPORATIVE EMISSION CONTROL under EMISSION SYSTEMS.

Cooling Fan

See MISCELLANEOUS CONTROLS.

EGR System

See EGR SYSTEM COMPONENTS under EMISSION SYSTEMS.

Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM.

Fuel Pump Control

See FUEL DELIVERY under FUEL SYSTEM.

Fuel Pressure Regulator Control (FPRC) Solenoid

See FUEL DELIVERY under FUEL SYSTEM.

Idle Air Control Valve

See IDLE SPEED under FUEL SYSTEM.

By-pass Air (BPA) Valve

See IDLE SPEED under FUEL SYSTEM.

Malfunction Indicator Light

See SELF-DIAGNOSTIC SYSTEM.

FUEL SYSTEM

The fuel system is controlled by PCM, based on data received from EEC system. The PCM monitors engine operating conditions based on input received from engine switches and sensors. Control of output actuators determines fuel mixture and idle speed.

Fuel Pump

Fuel is supplied by in-tank electric fuel pump. Pump delivers fuel from fuel tank, through 20-micron 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 air. Constant fuel pressure is maintained to injector nozzles by pressure regulator.

Fuel Pump Relay

The Fuel Pump Relay (FPR) ground circuit is controlled by the PCM. The FPR is activated while engine is cranking and running.

Fuel Pressure Regulator

Fuel pressure regulator is attached to fuel supply manifold assembly downstream of fuel injectors. It regulates fuel pressure supplied to injectors. Regulator is controlled by a vacuum actuated diaphragm inside of regulator. Diaphragm vacuum is suppled by the Fuel Pressure Regulator Control (FPRC) solenoid.

FPRC solenoid valve is controlled by an output signal from the PCM. The FPRC solenoid controls vacuum to fuel pressure regulator. During hot starts, the FPRC solenoid prevents fuel percolation by stopping fuel pressure regulator vacuum supply. This allows fuel rail pressure to increase to full pressure.

Inertia Fuel Shutoff (IFS) Switch

In the event of a collision or vehicle rollover, mechanical action within the inertia switch trips open ground circuit to the electric fuel pump. If the electrical circuit trips, it is not possible to restart the vehicle unless the switch is reset. A reset button is located on the switch assembly. IFS is located on right side of luggage compartment.

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 Air Control (IAC) Solenoid

IAC solenoid is an electromechanical device controlled by the PCM. The IAC solenoid is mounted on the throttle body and allows air to by-pass the throttle plate. The amount of air allowed to by-pass the throttle plate is determined by PCM and controlled by a duty signal.

Idle Air Control/By-Pass Air (IAC/BPA) Valve

IAC/BPA valve controls idle speed by regulating throttle plate by-pass air. ISC/BPA valve consists of air by-pass and idle air control solenoid valves. Air by-pass valve functions during cold engine conditions, at temperatures less than 140°F (60°C). Idle air control solenoid valve functions in all temperatures.

The air by-pass valve is controlled by the engine coolant temperature. The idle air control solenoid valve is controlled by the PCM.

See INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.

See INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.

DISTRIBUTOR IGNITION (DI)

The DI system uses an integral Ignition Control Module (ICM), Camshaft Position (CMP) sensor, 2 Crankshaft Position (CKP) sensors and the PCM to regulate ignition timing. The ICM and ignition coil are integral with the distributor. The CMP sensor is mounted in the distributor and sends a signal to the PCM. This signal is used for detection of cylinder No. 1 TDC position.

The CKP1 sensor is mounted in the distributor and creates 6 evenly spaced signals for each distributor revolution. These signals are used during start-up, in a back-up condition if the CKP2 sensor should fail or when the PCM STI terminal of the data link connector is grounded.

The CKP2 sensor is mounted to front of engine block below the crankshaft pulley. The CKP2 sensor signal is sent to the PCM when the projections of the signal rotor pass by the CKP2 sensor. This signal is used to control fuel injection timing, ignition timing, Idle Air Control (IAC) operation and engine speed detection when the PCM STI terminal of the data link connector is not grounded (except during starting).

Vacuum Control Valves (VCV)

Temperature-operated vacuum switches have 2 or more ports. They use wax pellet or bimetallic material to either open or close vacuum ports when normal engine operating temperature is reached. Valves are mounted in some part of cooling system so that the base is immersed in coolant.

Vacuum Reservoir

Vacuum reservoir stores vacuum to provide a consistent vacuum signal. It prevents rapid fluctuations or sudden drops in a vacuum signal, such as that seen during acceleration.

Vacuum Vent Valves

Valve controls 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 a combination of vent and delay valve. Valves should always be mounted so ports point downward.

Exhaust Gas Recirculation (EGR) Valve

The EGR valve recirculates a portion of the exhaust gas back into the engine to reduce the amount of oxides of nitrogen release during combustion and to reduce combustion temperature. The amount of exhaust gases that are released into the engine are proportional to engine load.

EGR Vacuum Regulator (EVR) Solenoid

EVR solenoid controls the vacuum applied to the EGR Modulator (EGRM) valve. The EVR solenoid is controlled by the PCM. Based on a series of inputs received from other components, the PCM determines when to activate the EVR solenoid. When EVR solenoid is deactivated, vacuum is vented to atmosphere.

See INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.

EGR Vent (EGRV) & EGR Control (EGRC) Solenoids

EGRC solenoid regulates vacuum supply to EGR valve. The EGRV solenoid vents vacuum to atmosphere in order to maintain EGR valve position. Both solenoids are controlled by output signals from PCM.

The CANP solenoid valve controls the amount of vapors drawn from carbon canister into the intake plenum. The PCM uses various inputs from sensors to determine calibration of vapor transfer.

When signaled by the PCM, CANP solenoid opens the passage between the carbon canister and the intake plenum. When de-energized, vacuum line to the purge valve is vented to the atmosphere. Carbon canister is purged by drawing vapors into air cleaner.

Carbon Canister

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

Fill Control/Vent System

Fill limiting is accomplished through configuration of fill neck and/or internal vent lines within fill 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 allows for thermal expansion of fuel and provides aid to in-tank vapor vent system.

Pressure/Vacuum Relief Fuel Cap

This system consists of a sealed filler cap with integral pressure/vacuum relief valve. Fuel system vacuum relief is provided after 1.0 in. Hg of vacuum; pressure relief is provided after 1.8 psi (.13 kg/cm 2 ). Under normal conditions, fill cap allows air to enter fuel tank as fuel is used, while preventing vapors from escaping.

Rollover Vent Valve

This valve releases excessive fuel tank pressure to atmosphere. If vehicle is rolled over, valve will prevent fuel tank drainage through evaporative hoses. Rollover vent valve is located on top of fuel tank.

Vapor Separator

The vapor separator allows vapor to vent to the carbon canister, while holding fluid in fuel tank. Vapors are routed through a single vapor line to carbon canister in engine compartment.

The vapor separator is located between fuel tank and evaporative lines to carbon canister. Venting fuel vapor prevents engine surging due to fuel enrichment and assists in hydrocarbon emission control.

POSITIVE CRANKCASE VENTILATION (PCV)

The PCV system uses intake manifold vacuum to extract blow-by vapors from crankcase. The mixture is then passed into the combustion chamber and burned. PCV valve provides control by metering flow of blow-by vapors according to manifold vacuum.

Under conditions where abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), the system is designed to allow excess gases to flow back through crankcase vent hose and into air inlet for consumption during normal combustion.

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 system malfunction during normal engine operation. For additional information, see G - TESTS W/CODES - EEC 2.5L article in the ENGINE PERFORMANCE section.

MISCELLANEOUS CONTROLS

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

A/C CLUTCH CYCLING PRESSURE SWITCH

On models with manual A/C system, the A/C clutch cycling pressure switch 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 A/C relay is controlled by an output signal from the PCM. The signal acts as a circuit on/off switch for the compressor magnetic clutch. The PCM will de-energize the A/C relay during Wide Open Throttle (WOT) conditions. This relay is sometimes referred to as a Wide Open Throttle Air Conditioning Cutoff (WAC) relay.

The PCM regulates operation of the electric cooling fan through the low fan and high fan control relays. Using information supplied by the A/C relay and Cooling Fan Engine Coolant Temperature (ECTF) sensor or Engine Coolant Temperature (ECT) sensor, the PCM controls cooling fan operation by grounding and ungrounding relay circuits.