Engine Controls - Theory & Operation - Eec-Iv Ford Taurus II

INTRODUCTION

Note. The CHECK ENGINE light, located in the instrument cluster, is referred to as Malfunction Indicator Light (MIL) in this article.

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.

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.

REVISED TERMINOLOGY

AIR INDUCTION SYSTEM

Note. The components listed here modify normal airflow to the engine. For inlet air sensors and meters, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.

Mark VIII

Each cylinder features 2 intake runners located between intake manifold and cylinder head. The primary runner feeds air to the cylinders whenever engine is running. The secondary runner is opened and closed by the IMRC vacuum actuator, which is controlled by the IMRC solenoid and Powertrain Control Module (PCM). With engine speed less than 3000 RPM, IMRC solenoid is energized by the PCM allowing vacuum to the IMRC vacuum actuator, closing the secondary runner. With engine speed more than 3000 RPM, solenoid is de-energized and vacuum is vented, allowing actuator to push secondary runner open. This system improves low and mid rangetorque, and improves fuel efficiency.

Taurus 3.0L SHO & 3.2L SHO

Each cylinder features 2 intake runners fed from an air plenum chamber that is connected to throttle housing. The primary runner feeds air to the cylinders whenever engine is running. The secondary runner is opened by an IDLE AIR CONTROL (IAC) valve when engine speed exceeds about 4000 RPM. This system improves low and mid range torque, and improves fuel efficiency.

SUPERCHARGER (THUNDERBIRD 3.8L SC)

The supercharger uses a pair of 3-lobed rotors connected to drive gears housed in the nose of the supercharger assembly. The supercharger drive gears are belt-driven from crankshaft. When rotated, the rotors create a positive displacement pump to compress air.

The compressed air creates a surplus volume of intake air that increases air pressure and density in the intake manifold. Air passes through supercharger and charge air cooler (formally intercooler) to the intake manifold. The throttle body controls the volume of air supplied to the supercharger through the intake plenum. A rev limiter begins closing off fuel to the injectors at about 6000 RPM.

A vacuum-controlled by-pass valve, installed at supercharger outlet, allows a regulated amount of airflow to return into supercharger at low RPM. As throttle opens, by-pass valve closes and directs all air from the supercharger to intake manifold.

The supercharger is serviced as an assembly, and overhaul is not recommended. The supercharger system includes the boost control solenoid, charge air cooler, knock sensor, knock control unit, overboost warning device and vane air temperature sensor.

Charge Air Cooler (CAC)

As air is compressed, its temperature increases. This heated, pressurized air is routed through the core of the CAC. Outside air passing through the CAC lowers the temperature of the compressed air inside CAC. This allows a denser air/fuel charge to enter combustion chamber and improve efficiency.

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 (PCM) LOCATIONS 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.

The Malfunction Indicator Light (MIL) will remain on whenever FMEM is in operation. FMEM substitutes a fixed sensor signal and continues to monitor the failed sensor. If the signals from a faulty sensor return to within operating limits, the PCM will resume using the sensor'ssignal.

POWERTRAIN CONTROL MODULE (PCM) LOCATIONS

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 PCM and EEC-IV system.

Variable Control Relay Module (VCRM)

VCRM interfaces with the Powertrain Control Module (PCM) to control cooling fan, A/C clutch control, A/C head pressure control and fuel pump operation. The VCRM also supplies power to the PCM and EEC-IV system.

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.

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

Barometric Pressure (BARO) Sensor

BARO sensor measures barometric pressure of atmosphere. Variations in atmospheric pressure are converted to electrical signals and sent to PCM. The PCM uses this signal to adjust fuel mixture due to changes in altitude. The BARO sensor affects air/fuel ratio, EGR flow and spark advance.

The sensor looks the same as Manifold Absolute Pressure (MAP) sensor, except the tubing nipple on BARO sensor is vented to the atmosphere and MAP sensor is connected to the intake manifold.

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 primarily by the torque converter clutch lock/unlock strategy.

Camshaft Position (CMP) Sensor

CMP sensor is a Hall Effect magnetic switch. The Hall Effect switch is activated by a single vane, which is driven by the camshaft. The CMP sensor provides cylinder identification information during engine start-up for PCM to initiate correct firing order.

Coolant Temperature Sensor

See ENGINE COOLANT TEMPERATURE (ECT) SENSOR.

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.

Data Link Connector (DLC) & Self-Test Input (STI) Connector - The 6-pin Data Link Connector (DLC) is used to perform the Quick Test diagnostic procedure. The STI is a single-pin connector located next to the DLC. When the STI wire is connected to SIG RTN terminal of DLC, fault code output function is activated.

Differential Pressure Feedback EGR (DPFE) Sensor

DPFE sensor monitors exhaust system and generates a varying electrical signal proportionate to exhaust pressure. This signal is sent to the PCM where it is translated and used to compute correct EGR flow.

Exhaust Gas Recirculation Temperature (EGRT) Sensor

EGRT sensor resistance varies with temperature. Sensor is located downstream of EGR valve and its resistance decreases as EGR flow increases. The Powertrain Control Module (PCM) uses EGRT sensor input as an indication that EGR system is functioning properly.

EGR Valve Position (EVP) Sensor

EVP sensor detects EGR valve position. This information is transmitted to the PCM. The sensor is mounted on the EGR valve. The EVP signal affects EGR flow and ignition timing.

Engine Coolant Temperature (ECT) Sensor

ECT sensor inputs coolant temperature to the PCM. ECT sensor is threaded into heater outlet fitting or coolant passage. The ECT sensor changes resistance in response to coolant temperature. The ECT sensor resistance decreases as coolant temperature increases.

Flexible Fuel (FF) Sensor

FF sensor is a capacitive device with a signal processing stage. FF sensor is located in engine compartment, high-pressure fuel supply line between fuel mixer and fuel rail. FF sensor frequency signal varies according to conductivity and temperature of methanol-gasoline mixture. As percentage of methanol in fuel increases, output frequency of FF sensor signal will increase. For example, a fuel mixture that was determined to be 30 percent methanol will result in FF sensor signal output frequency being 60-100 Hz. Sixty percent methanol will result in FF sensor signal of 90-130 Hz. The PCM uses FF sensor frequency signal to calculate correct air/fuel ratio and spark advance.

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 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. All V6 and V8 engines are equipped with 2 sensors, one for each exhaust bank.

Intake Air Temperature (IAT) Sensor

IAT sensor inputs air temperature to the PCM. The IAT sensor changes resistance in response to air temperature. The ECT sensor resistance decreases as air temperature increases.

Knock Sensor (KS)

KS measures vibrations (pre-ignition) and converts them into an electrical signal. The PCM monitors signal from KS and adjusts ignition timing if pre-ignition occurs. Mark VIII is equipped with 2 sensors. KS is threaded into the engine block.

Manifold Absolute Pressure (MAP) Sensor

MAP sensor responds to manifold vacuum changes due to engine load and speed changes. Manifold pressure and temperature are used to calculate the airflow rate to the PCM.

The MAP sensor uses frequency to measure manifold vacuum. Map sensor frequency increases as vacuum increases. 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 proportional to 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) hotter than the cold wire located downstream of hot wire. As air passes through airflow sensor, the air temperature is measured as it passes over the cold wire sensor. The PCM uses this information to calculate the required injector pulse width in order to provide desired air/fuel ratio.

Park/Neutral Position (PNP) Switch

PNP switch monitors transmission gear selection and signals the PCM. This signal affects air/fuel ratio and idle speed.

Power Steering Pressure (PSP) Switch

PSP switch monitors power steering pressure. On Probe 2.0L M/T, switch is normally open and closes when power steering pressure increases as wheels are being turned. On all other models, switch is normally closed and opens when pressure increases. The PCM uses PSP signal to adjust idle speed to compensate for additional load on engine.

Pressure Feedback EGR (PFE) Sensor

PFE sensor monitors exhaust system and generates a varying electrical signal proportionate to exhaust pressure. This signal is sent to the PCM where it is translated and used to compute correct EGR flow.

Programmable Speedometer/Odometer Module (PSOM)

PSOM receives input from Rear Anti-Lock Brake Sensor (RABS). The RABS is mounted to rear axle differential. The PSOM signal is used by speed control module and the PCM.

Throttle Position (TP) Sensor

TP sensor monitors throttle plate opening. Its signal to the PCM is proportional to throttle plate opening angle. 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 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 the PCM. The PCM uses this input signal to determine transmission fluid temperature.

Transmission Speed Sensor (TSS)

TSS is a magnetic pick-up that sends a signal to the PCM. The PCM uses this signal to determine transmission RPM.

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/transaxle 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 Clutch Cycling Pressure Switch

See MISCELLANEOUS CONTROLS.

By-Pass Air (BPA) Valve

See IDLE SPEED under FUEL SYSTEM.

Canister Purge Valve

See EVAPORATIVE EMISSION SYSTEM under EMISSION SYSTEMS.

Canister Purge Solenoid Valve

See EVAPORATIVE EMISSION 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 is supplied by an in-tank electric fuel pump. Fuel pump is capable of pumping 38 gallons of fuel per hour at a working pressure of 39.2 psi (2.8 kg/cm 2 ). Pump has an internal pressure relief valve to protect against over-pressure due to fuel flow restriction. 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. Constant fuel pressure is maintained to injector nozzles by 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.

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.

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 unless the switch is reset. A reset button is located on the switch assembly.

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 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 ON time.

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.

BPA valve, mounted on the throttle body, controls idle quality by regulating throttle plate by-pass air. BPA valve consists of an air by-pass valve, which functions during cold engine conditions below 122°F (50°C), and the idle speed control motor, which works through the entire temperature range. The air by-pass valve is controlled by the engine coolant temperature. The idle speed control motor is controlled by the PCM.

IAC solenoid is an electromechanical device controlled by the Powertrain Control Module (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.

1.9L, 3.0L (Flexible Fuel) & 4.6L

The EI (high data rate) system (formally Electronic Distributorless Ignition System - EDIS) consists of a Crankshaft Position (CKP) sensor, Ignition Control Module (ICM) and one 4-tower coil pack (one 6-tower coil pack on 3.0L or two 4-tower coil packs on 4.6L).

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 90 degrees 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 CPK 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.

Scheme 1

2.3L Mustang

The 2.3L Mustang (dual plug) EI (low data rate) system (formally Distributorless Ignition System - DIS) consists of a crankshaft-mounted dual Hall Effect sensor, two 4-tower coil packs and an Ignition Control Module (ICM).

The EI system eliminates need for a distributor by using multiple ignition coils. Each coil fires 2 spark plugs simultaneously. Spark plugs are paired so as one fires during the compression stroke, the other fires during the exhaust stroke. On the next cycle, firing strategy is reversed. Although spark in exhaust stroke is wasted, little secondary energy is lost.

Two coils are mounted together in a coil pack. Each coil pack has 2 tach wires (one for each coil). Since there are 2 plugs per cylinder, 2 coil packs are required. The right coil pack operates continuously, but the left coil may be switched on or off by the PCM. The PCM computes spark angle and dwell for the ignition system.

The Crankshaft Position (CKP) sensor is a dual digital output Hall Effect device that responds to 2 rotating metallic shutters mounted together on crankshaft. One output signal from Hall Effect sensor, Profile Ignition Pick-Up (PIP), is a 50 percent duty cycle signal (50 percent on and 50 percent off) which provides base spark timing information. The other output signal, Cylinder Identification (CID), is required so the ICM knows which coil to fire. The CID is also used by PCM for fuel timing.

The PCM determines spark angle using PIP signal to establish base timing. The Spark Output (SPOUT) signal is produced and sent by PCM to the ICM and serves 2 purposes. The leading edge fires the coil, and the trailing edge controls dwell time. This feature is called Computer Controlled Dwell (CCD).

The Ignition Diagnostic Monitor (IDM) is an output signal from the ICM to the PCM which provides diagnostic information about the ignition system for Self-Test.

Dual Plug Inhibit (DPI) allows the PCM to switch ignition system from single-plug to dual-plug operation. During engine cranking, vehicle is in single-plug mode; only plugs on right side of the engine are firing. The PCM sends a command to ICM to switch to dual-plug operation.

If CID circuit fails, ICM will randomly select one of 2 coils to fire. If hard starting results, turning key off and then cranking again will result in ICM selecting another coil to fire. Several attempts may be needed until proper coil is selected, allowing vehicle to be started and driven until repairs can be made. The Failure Mode Effects Management (FMEM) system will keep the vehicle drivable in the event of EEC-IV system or ignition failures that would otherwise prevent spark angle or dwell commands. During FMEM, PCM opens the SPOUT line and ICM fires coils directly from PIP output. This results in a fixed spark angle of 10 degrees and fixed dwell.

3.0L SHO, 3.2L SHO & 3.8L SC

The 3.0L SHO, 3.2L SHO and 3.8L SC Electronic Ignition (EI) system (low data rate) consists of a crankshaft-mounted Hall Effect sensor, camshaft-driven Hall Effect sensor, a 6-tower coil pack and Ignition Control Module (ICM).

The EI system eliminates the distributor by using multiple ignition coils. Each coil fires two spark plugs simultaneously. The spark plugs are paired so one fires during compression stroke and the other fires during exhaust stroke. Three coils are mounted together in a coil pack. The coil pack has 3 tach wires, one for each coil. The crankshaft sensor is a digital output Hall Effect sensor that responds to a rotating metallic vane mounted on the crankshaft damper assembly.

Cylinder Identification (CID) signal is generated by Hall Effect camshaft sensor. The vane cup has one tooth and is driven by the camshaft. On 3.0L SHO and 3.2L SHO, sensor is mounted at the end of rear camshaft. On 3.8L SC, sensor is mounted in the normal distributor location. On all models, the Profile Ignition Pick-Up (PIP) output is a 50 percent duty cycle (50 percent on and 50 percent off) signal which provides base spark timing information. The CID signal output is also a 50 percent duty cycle signal and is required so ICM knows which coil to fire. The PCM also uses CID signal for fuel timing.

The PCM determines spark angle using the PIP signal to establish base timing. Spark Output (SPOUT) signal is sent from PCM to the ICM and serves 2 purposes. The leading edge fires the coil, and trailing edge controls dwell time. This feature is called Computer Controlled Dwell (CCD).

The Ignition Diagnostic Monitor (IDM) is an output from ICM. IDM provides diagnostic information concerning ignition system to PCM for self-test. IDM is also input signal for vehicle tachometer. If CID circuit fails, ICM will randomly select one of 3 coils to fire.

If hard starting results, turning key off and then cranking again will result in ICM selecting another coil to fire. Several attempts may be needed until proper coil is selected, allowing vehicle to be started and driven until repairs can be made. The Failure Mode Effects Management (FMEM) system attempts to keep vehicle driveable in spite of certain EEC-IV system failures that prevent the PCM from providing spark angle or dwell commands. The PCM opens SPOUT line and ICM fires the coils directly from PIP input. This results in a fixed spark angle of 10 degrees and fixed dwell.

DISTRIBUTOR IGNITION (DI)

The DI system (formally Thick Film Ignition-IV (TFI-IV) system) has 2 distinct configurations. In the first configuration, the Ignition Control Module (ICM) is mounted on the distributor. The ICM has 3 pins, which plug into the Hall Effect Camshaft Position (CMP) sensor located within the distributor. In the second configuration, the ICM is not mounted on the distributor but in another location within the engine compartment.

The components of both configurations consist of ICM, distributor CMP sensor and "E" core ignition coil. The distributor used on the distributor mounted ICM is a universal distributor that has an opening in it for the ICM. The distributor used on remote mounted ICM is a sealed distributor. On both distributors, the CMP is located within the distributor. There are no mechanisms within either distributor for centrifugal or vacuum advance.

The CMP sensor responds to a rotating metallic shutter on the distributor shaft and produces a Profile Ignition Pick-Up (PIP) signal. The PIP signal provides base timing information and is an indication of engine RPM and position. Since the shutter is mounted on the distributor shaft, 2 engine crankshaft revolutions are required to fire each spark plug once. This is because distributor rotates at half of crankshaft speed.

The internal circuitry of the ICM will have one of 2 arrangements, push start or Computer Controlled Dwell (CCD). The push start system allows for increased dwell, or coil ON time, when starting engine. The ICM determines when to turn coil on based upon engine RPM information. The coil is then turned on or off, whenever a rising edge of a Spark Output (SPOUT) signal is encountered. The SPOUT signal is a digital signal generated by the Powertrain Control Module (PCM) providing spark angle information to the ICM. The SPOUT signal controls only the firing of the coil. The falling edge of the SPOUT signal is ignored.

The CCD system is same as push start system except the falling edge of the SPOUT signal is now generated to control coil ON time. The coil ON time, or dwell is entirely controlled by the SPOUT signal. The ICM does not internally determine when to turn the coil on as it does on the push start system. On the CCD system, the ICM responds directly to the SPOUT signal it receives.

EMISSION SYSTEMS

Several systems and components are used to control emissions. Operation and method of actuation is provided for most devices. For testing procedures, refer to specific system in appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Air Cleaner Temperature Sensor

This bimetallic sensor is installed in the lower air cleaner tray and is subject to temperature changes within the air cleaner. At a given temperature, the sensor bleeds off vacuum to the air cleaner air control door, permitting vacuum motor to open the duct door and allow fresh air in while shutting off full heat.

Temperature Vacuum Switch (TVS)

TVS incorporates a bimetallic disc to open or close vacuum ports and may be used in conjunction with distributor, canister purge or EGR systems.

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 when normal engine operating temperature is reached.

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 Delay Valves

Valves are inserted in vacuum lines to provide for gradual application or release of vacuum to engine or emission control devices. Valves may be 1-way or 2-way design, depending on function and part of system affected.

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. May be vent valve only or combined vent and delay valve. Valves should always be mounted so ports point downward.

AIR INJECTION SYSTEMS

The air injection system reduces carbon monoxide (CO) and hydrocarbon (HC) content of exhaust gases. It injects fresh air into the exhaust gas stream, which continues combustion of unburned gases. Individual systems may vary in number and types of components, depending on engine size and application.

Pulsed Secondary Air Injection (PAIR) System

The PAIR system does not use an air pump. Natural pulses present in the exhaust system are used to pull air into the exhaust system through a pulse air valve. The pulse air valve is connected to catalytic converter by a tube and to air cleaner by a hose. This allows fresh air to complete oxidation of exhaust gases and blocks backflow of high pressure exhaust pulses.

Secondary Air Injection (AIR) System

Individual systems may vary in number and types of components, depending upon engine size and application, but all systems use the same basic components. A typical system consists of an air supply pump, air by-pass valve, air diverter valve, check valve(s), air manifold and air hoses.

In the AIR system, air can be by-passed to the atmosphere by a Secondary Air By-Pass (AIRB) valve and/or directed to exhaust manifold or catalytic converter by a Secondary Air Injection Diverter (AIRD) valve. Some models may use a combined AIRB/AIRD valve.

Air By-Pass (AIRB) Valve

The AIRB valve directs airflow from air pump to exhaust system or atmosphere as required. Valve may be mounted on air pump or in-line (remote). AIRB valve is vacuum-operated and may be normally open or closed.

Normally closed valve supplies air to the exhaust system with medium and high applied vacuum signals during normal modes, short idles and some acceleration. With low or no vacuum applied, pumped air is dumped through silencer ports of the valve or through the dump port.

Normally open valve with a vacuum vent provide a timed air dump during deceleration and also dump when vacuum pressure difference is maintained between signal port and vent port.

Pulsed Secondary Air Injection (PAIR) Valve

PAIR valve functions as a one-way check valve, allowing secondary air to enter exhaust system while preventing exhaust gases from passing in the opposite direction. Valve is normally closed.

Air Injection Diverter (AIRD) Valve

AIRD valve is operated by vacuum and directs air pump output to exhaust manifold or downstream to catalytic converter, depending on system requirements, engine mode and control system.

Air Injection (AIR) Solenoid

Solenoid is normally closed and consists of 2 vacuum ports with an atmospheric vent. The solenoid outlet port is open when activated and closed with deactivated. When activated, the outlet port is open to the inlet port and closed to atmospheric vent.

Air Pump

Air pump supplies air under pressure to exhaust port near exhaust valve by either an external air manifold or through an internally drilled passage in cylinder head or exhaust manifold. This pressurized air, combined with hot exhaust gases, creates a secondary combustion stage and decreases tailpipe emissions.

The air pump is a belt-driven, positive displacement, vane-type pump that provides air for the 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. Air pumps are available in various sizes. Various drive belt pul-ley ratios permit a wider range of vehicle applications.

Air Silencer/Filter

Air silencer, mounted in engine compartment, is a combination silencer and filter. It is connected to system by a flexible hose. This component is used on pulse air injection systems.

Check Valve

Check valves are used on all air injection systems in various locations. Check valve allows airflow in one direction only.

Combination Air Injection By-Pass (AIRB) & Air Injection Diverter (AIRD) Valve

Combination AIRB/AIRD valve combines the functions of the AIRB valve and the AIRD valve into a single unit. Valve is located in air supply line between air pump and upstream/downstream air supply check valves. The AIRB portion of the valve controls flow of secondary air to the exhaust system or allows secondary air to be by-passed to atmosphere. When air is not being by-passed, the AIRD portion of the valve switches the air injection point to either upstream or downstream location.

Dual Air Control Solenoids - Dual air control solenoid valve assembly consists of 2 normally closed solenoid valves with vents. One valve controls Air Injection By-Pass (AIRB) valve and the other controls Air Injection Diverter (AIRD) valve. Both valves pass air when deactivated and do not pass air when activated.

Note. Not all listed components are used on any one system. Component usage depends on calibration of vehicle.

Electronic EGR (EEGR) Valve

EEGR valve is required in EEC-IV systems when EGR flow is monitored by EGR Valve Position (EVP) sensor. The EGR valve is operated by a vacuum signal from EGR electronic vacuum regulator.

EGR Vacuum Regulator (EVR) Solenoid

EVR solenoid controls vacuum output to EGR valve. When EVR solenoid is de-energized, solenoid valve opens allowing manifold vacuum to be applied to EGR valve. When solenoid valve is energized, solenoid valve is closed and vacuum is vented to atmosphere.

EVP sensor is attached to the EGR valve assembly and indicates position of EGR valve to the PCM. Valve is located on top of EGR valve.

EVAPORATIVE EMISSION SYSTEM

Note. Not all of the following components are used on any one system. Usage depends on calibration of vehicle.

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. For specific component application and vacuum hose routing, see VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section.

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, solenoid valve is energized and opens, purging fuel vapors into engine.

Canister Purge (CANP) Valve

CANP valve is a part solenoid, part valve component that is used by the PCM to regulate flow of fuel vapors from fuel evaporation canister to fuel system. The CANP valve regulates the 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. 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, filler cap allows air to enter fuel tank as fuel is used, while preventing vapors from escaping.

Vapor Vent System

System provides a vapor space above gasoline surface in fuel tank. 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 arepurged 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 G - EEC-IV TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

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-IV system malfunction during normal engine operation. For additional information, see G - EEC-IV TESTS W/ CODES 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 (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.

Solenoids

The A4LD, AXODE and AODE transmissions use 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.