Engine Controls - Theory & Operation - Eec-Iv Ford Escort 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.

AIR INDUCTION SYSTEM

Note. The components listed here are components that modify the normal airflow to the engine. For inlet air sensors and meters, see INPUT DEVICES in this article.

SUPERCHARGERS (THUNDERBIRD 3.8L SC)

Supercharger is an option on the 3.8L Thunderbird. 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 the 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 intercooler to the intake manifold. The throttle body controls the volume of air supplied to the supercharger through the intake plenum.

The supercharger is serviced as an assembly, and overhaul is not recommended. The supercharger system includes the boost control solenoid, intercooler, knock sensor, knock control unit, overboost warning device and vane air temperature sensor. A rev limiter begins closing off fuel to the injectors at about 6000 RPM.

Intercooler

As air is compressed, its temperature increases. This heated, pressurized air is routed through the core of the intercooler. Outside air passing through the intercooler lowers the temperature of the compressed air inside intercooler.

The intercooler lowers temperature of compressed air from the supercharger and increases inlet air density. This allows a denser air/fuel charge to enter combustion chamber and improve efficiency.

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.

INTAKE AIR CONTROL (IAC) SYSTEM (TAURUS 3.0L 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 IAC valve when engine speed exceeds about 4000 RPM. This system improves low and mid range torque and improves fuel efficiency.

CONTROL UNIT

The Electronic Control Assembly (ECA) monitors engine operating conditions by input received from engine switches and sensors. Control of output actuators determines fuel mixture and idle speed. For ECA location, see ELECTRONIC CONTROL ASSEMBLY (ECA) LOCATIONS table.

The engine control system consists of the ECA, relays, sensors, switches and actuators. The ECA sends out electrical reference signals to engine sensors and then analyzes the return signals. The engine sensors supply the ECA with specific information, in the form of electrical signals, to determine engine operating conditions. In the event of a sensor or actuator failure, the ECA initiates an alternative strategy called Failure Mode Effects Management (FMEM) to allow the vehicle to maintain driveability.

The CHECK ENGINE light 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 ECA will resume using the sensor's signal.

ELECTRONIC CONTROL ASSEMBLY (ECA) LOCATIONS

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 the WIRING DIAGRAMS article in this section. The available input signals include the following

Air Charge Temperature (ACT) Sensor

ACT sensor is located in the intake tract or in the air cleaner. It provides ECA with intake air temperature information. The ECA uses this information to adjust fuel mixture, primarily during cold-start enrichment periods.

Barometric Pressure (BP) Sensor

Sensor measures barometric pressure of atmosphere. Variations in atmospheric pressure are converted to electrical signals and sent to ECA. The ECA uses this signal to adjust fuel mixture due to changes in altitude. The BP sensor affects air/fuel ratio and idle speed.

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

Brake On-Off (BOO) Switch

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

Camshaft Sensor

The camshaft sensor is a Hall Effect magnetic switch. The Hall Effect switch is activated by a single vane, which is driven by the camshaft. Camshaft sensor provides cylinder identification information.

Clutch Engage Switch

Switch is mounted at the clutch pedal. It signals the ECA when the transmission is in gear. Clutch engage switch signal to the ECA affects air/fuel ratio and idle speed.

Coolant Temperature Sensor

See ENGINE COOLANT TEMPERATURE (ECT) SENSOR.

Crankshaft Angle Sensor

The crankshaft angle 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 Pickup (PIP) is a crankshaft position signal that is sent to the ECA. The PIP signal generated by the Hall Effect sensor provides base timing and RPM information to the ECA .

Cylinder Identification (CID) Sensors

CID sensors are used to detect TDC position for cylinders No. 1 and 4. This signal affects injector and ignition timing.

Exhaust Gas Oxygen (EGO) Sensor

The voltage signal produced by the EGO sensor indicates the oxygen content of engine exhaust gases. The EGO sensor is threaded into the exhaust manifold.

EGR Valve Position (EVP) Sensor

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

Engine Coolant Temperature (ECT) Sensor

This sensor inputs the coolant temperature to the ECA. The ECT is threaded into the heater outlet fitting or an engine coolant passage near the thermostat housing. The signal from the ECT affects the following

1. Air/Fuel Ratio
2. Idle Speed
3. EGR Flow
4. Purge Flow
5. Fuel Pressure
6. Ignition Timing Output Signal From ECA

Heated Exhaust Gas Oxygen (HEGO) Sensor

An electrically heated O2 sensor is mounted in the exhaust manifold. This sensor monitors oxygen content of exhaust gases. When EGO is at operating temperature, a voltage signal is produced, which varies according to oxygen content of exhaust gases. Signal is transmitted to the ECA and is translated into a rich or lean mixture signal.

HEGO sensor uses a built-in heating circuit. The heating circuit is used to bring the HEGO sensor up to operating temperature, enabling faster conversion to closed-loop operation. With the exception of 3.0L PFI engine, all V6 and V8 engines are equipped with 2 sensors: one for each exhaust bank.

Knock Sensor (KS)

The KS measures vibrations and converts them into an electrical signal. The signal is sent to the Knock Control Unit (KCU) where it is filtered and sent to the ECA. The KS is threaded into the engine block, near the oil pressure switch.

Manifold Absolute Pressure (MAP) Sensor

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

The MAP sensor uses frequency to measures manifold vacuum. The MAP sensor is used as a barometric sensor for altitude compensation, updating the ECA during Key On, Engine Off (KOEO) and at Wide Open Throttle (WOT). By monitoring MAP sensor output voltage, the ECA can determine correct rate of spark advance, EGR flow and air/fuel ratio. If MAP sensor fails, the ECA will supply a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel distribution. See INPUT DEVICES in this article.

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) located downstream of hot wire. As air passes through the airflow sensor, the temperature of the air is measured as it passes over the cold wire sensor. The ECA uses this information to control fuel delivery.

Neutral Gear Switch (NGS)

The NGS monitors in-gear conditions and signals the ECA. This signal affects air/fuel ratio, idle speed and ignition timing.

Power Steering (P/S) Pressure Switch

The P/S pressure switch monitors power steering pressure. When the power steering is in operation, the switch signals the ECA. The switch is located in the high pressure line, between P/S pump and steering rack assembly. The P/S signal affects the idle speed.

Self-Test Output/Self-Test Input (STO/STI) Connectors

The STO connector is a 6-pin connector that is used to perform the Quick Test diagnostic procedure. The STI is a single-pin connector located next to the STO. When the STI is grounded, it activates the fault code output function. Codes are retrieved through the STO connector.

Throttle Position Sensor (TPS)

The TPS monitors throttle plate opening. Its signal to the ECA is proportional to throttle plate opening angle. TPS is mounted on throttle body, at throttle plate rod. The TPS signal affects air/fuel ratio, injector timing, idle speed, EGR flow and ignition timing.

Vehicle Speed Sensor (VSS)

Sensor is transmission-mounted and sends a constant pulse signal to the ECA 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 on each output component, refer to the system indicated after component.

1. A/C Clutch Cycling Pressure Switch - See MISCELLANEOUS CONTROLS.
2. Canister Purge Solenoid Valve - See EMISSION SYSTEMS.
3. CHECK ENGINE Light - See SELF-DIAGNOSTIC SYSTEM.
4. Cooling Fan - See MISCELLANEOUS CONTROLS.
5. EGR System - See EMISSION SYSTEMS.
6. Fuel Injectors - See FUEL CONTROL.
7. Fuel Pump - See FUEL DELIVERY.
8. Fuel Pressure Regulator - See FUEL DELIVERY.
9. By-Pass Air Control (BAC) Valve - See IDLE SPEED.
10. Self-Diagnostic - See SELF-DIAGNOSTIC SYSTEM.

Fuel Pump

Fuel is supplied by chassis-mounted or in-tank electric fuel pump. Some models use both in-tank low pressure pump and externally mounted high pressure 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 fuel pressure regulator.

Fuel Pressure Regulator

Fuel pressure regulator regulates fuel pressure supplied to injectors. Fuel pressure regulator is attached to fuel supply manifold assembly, downstream of fuel injectors. Regulator is diaphragm operated relief valve in which 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.

Fuel Pump Shut-Off (Inertia) Switch

In the event of a collision or vehicle roll-over, electrical contacts within the inertia switch open, and fuel supply to the electric fuel pump is shut off. Fuel supply will be interrupted even if the engine is still running.

A reset button is located on the switch assembly. If the electrical circuit trips, it is not possible to re-start the vehicle unless the switch is reset by depressing the reset button. Anytime the switch opens, the fuel system should be inspected for damage prior to resetting.

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

Fuel Injectors

The electronic fuel injection system is a pulse time PFI system. The ECA controls fuel injectors to meter fuel quantity into intake ports. The ECA receives inputs from engine sensors to compute fuel flow necessary to maintain air/fuel ratio throughout entire engine operational range. Injector ON time is the only controlled variable in fuel delivery system. The ECA controls length of time each injector is on, or energized.

Each cylinder has a solenoid-operated injector that sprays fuel toward 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 ECA-controlled ground circuit is used to complete the circuit and energize (on time) the injector. The on time governs the amount of fuel delivered.

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. Atomization spray is obtained by shape of pintle.

By-Pass Air Control (BAC) Valve

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

1.9L Escort, 1.9L Tracer & 4.6L Town Car

The Electronic Distributorless Ignition System (EDIS) consists of a Variable Reluctance Sensor (VRS), EDIS Ignition Module and one 4-tower coil pack (2 coil packs on 4.6L).

The EDIS operates by sending crankshaft position information from VRS to EDIS module. The module generates a Profile Ignition Pickup (PIP) signal and sends it to ECA.

The ECA responds with a Spark Angle Word (SAW), processes the VRS and SAW signals and decides which coils to fire. In addition, the module generates an Ignition Diagnostic Monitor (IDM) signal to ECA, which is used to indicate a failure mode and provide a tach output signal.

The VRS is a passive electromagnetic device that senses movement of a 36 minus one-tooth wheel, located behind the crankshaft pulley. An A/C voltage signal is generated, which increases with engine RPM and provides engine speed and crankshaft position information to EDIS module.

The EDIS module is a microprocessor-based device with coil drivers. EDIS Module makes decisions about spark timing and coil firing. The module turns coils on and off at the correct time and in proper sequence, based on information from VRS and a pulse width modulated signal (SAW) generated from ECA. The module receives VRS and SAW signals and produces PIP and IDM output signals, which are sent to ECA.

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

The coil is turned on (coil charging) by EDIS module, and then turned off, firing two 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. The next time the coil is fired, the roles are reversed.

2.3L Mustang

The 2.3L Mustang (Dual Plug) Distributorless Ignition System (DIS) consists of a crankshaft-mounted dual Hall Effect sensor, two 4-tower DIS coil packs and a DIS ignition module.

The DIS eliminates need for a distributor by using multiple ignition coils. Each coil fires two spark plugs at same time. Spark plugs are paired so as one fires during the compression stroke, the other fires during the exhaust stroke. The next time same pair of plugs are fired, the roles are reversed. Although spark in exhaust stroke is wasted, little of coil's energy is lost.

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

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

The ECA determines spark angle using PIP signal to establish base timing. The Spark Output Signal (SPOUT) is produced and sent by ECA to the DIS module and serves two 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 DIS module to the ECA that provides diagnostic information about the ignition system for Self-Test.

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

If CID circuit fails, DIS module will randomly select one of 2 coils to fire. If hard starting results, turning key off and then cranking again will result in DIS module 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, ECA opens the SPOUT line and DIS module fires coils directly from PIP output. This results in a fixed spark angle of 10 degrees and fixed dwell.

3.0l SHO Taurus & 3.8l SC Thunderbird

The 3.0L SHO and 3.8L SC Distributorless Ignition System (DIS) consists of a crankshaft-mounted Hall Effect sensor, camshaft-driven Hall Effect sensor, a 6-tower DIS coil pack and DIS ignition module.

The DIS eliminates the distributor by using multiple ignition coils. Each coil fires two spark plugs at same time. 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.

The Cylinder Identification (CID) signal is generated by camshaft sensor, which is also a Hall Effect sensor. The vane cup has one tooth and is driven by the camshaft. The Profile Ignition Pick-Up (PIP) output is a 50 percent duty cycle (50 percent on and 50 percent off) signal that provides base spark timing information. The CID signal output is also a 50 percent duty cycle signal and is required so DIS module knows which coil to fire. ECA also uses CID signal for fuel timing.

The ECA determines spark angle using the PIP signal to establish base timing. Spark Output Signal (SPOUT) is sent from ECA to the DIS module 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 DIS module. IDM provides diagnostic information concerning ignition system to ECA for self-test. IDM is also input signal for vehicle tachometer. If CID circuit fails, DIS module will randomly select one of 3 coils to fire.

If hard starting results, turning key off and then cranking again will result in DIS module 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 ECA from providing spark angle or dwell commands. The ECA opens SPOUT line and DIS module fires the coils directly from PIP input. This results in a fixed spark angle of 10 degrees and fixed dwell.

ELECTRONIC IGNITION SYSTEM (THICK FILM IGNITION IV)

The Thick Film Ignition IV (TFI-IV) system is a forth generation system. A gear-driven distributor houses a Hall Effect sensor called a Profile Ignition Pick-Up (PIP) sensor. This sensor is used to trigger the ignition coil. This distributor does not use conventional centrifugal/vacuum advance mechanisms. The TFI module may be mounted in the base of the distributor bowl or on the cowl behind engine.

Distributors that do not contain TFI module are called Closed Bowl Distributor (CBD) systems. TFI systems use Hall Effect switch mechanism to switch primary voltage and send a PIP signal to the ECA. The ECA uses PIP input signal to produce a Spark Output Signal (SPOUT) that is sent to TFI ignition module to be used to trigger the discharge of coil secondary voltage. Dwell is controlled by TFI module on some models and by ECA on others. When dwell is controlled by the ECA, it is a Computer Controlled Dwell (CCD) system. Vehicles with CCD must have a CBD, but not all CBD systems have CCD.

The TFI ignition module used on manual transaxle-equipped vehicles features a push start mode. This feature allows vehicle to be push started if necessary. An "E" core ignition coil is used with all TFI systems.

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 tests in the appropriate I - SYS/COMP TESTS article in this 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.

Exhaust Heat Control Valve

Valve is used to divert hot gases from the exhaust manifold to the intake manifold riser pad to heat the incoming air/fuel charge. Two types are used: a bimetallic spring type and a vacuum-actuated type.

Solenoid Vacuum Valve

Solenoid valve is used on throttle kicker and EGR shutoff. The normally closed solenoid valve consists of 2 vacuum ports with an atmospheric vent. Valve assembly can be with or without a control bleed. The control bleed is provided to prevent contamination entering solenoid valve from intake manifold. When de-energized, outlet port of valve is opened to atmospheric vent and closed to inlet port. When energized, outlet port is opened to inlet port and closed to atmospheric vent.

Temperature Vacuum Switch (TVS)

The 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 on its top.

Vacuum Delay Valves

Valves are inserted in vacuum lines to provide for gradual application or release of vacuum to engine or emission control devices. May be one-way or two-way valves depending on function and part of system affected.

Vacuum Reservoir

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

Controls 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 SYSTEM

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.

Pulse Air Valve System

The pulse air valve replaces the air pump on some thermactor systems. It permits air to be drawn into exhaust system by vacuum created by exiting exhaust pulse.

Natural pulses present in the exhaust system are used to pull air into exhaust manifold through a pulse air valve. The pulse air valve is connected to exhaust manifold 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.

Thermactor 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, centrifugal filter, check valve(s), air control valve, air manifold and air hoses.

In the Managed Thermactor Air (MTA) system, air can be by-passed to the atmosphere by a thermactor air by-pass valve and/or directed near exhaust manifold or underbody catalytic converter. Some models may use a combined air by-pass/air control valve.

Anti-Backfire (Gulp) Valve

The anti-backfire valve, located downstream from the air by-pass valve, diverts a portion of thermactor air to intake manifold during periods of sudden decrease of intake manifold pressure.

Air By-Pass Valve

Valves direct airflow from thermactor air pump to exhaust system or atmosphere as required. They may be mounted on air pump or in-line (remote). Air By-Pass Valves are vacuum-operated and may be normally open or closed.

Normally closed valves supply 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, the pump air is dumped through the silencer ports of the valve.

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

Air Check Valve & Pulse Air Valve

Both units function as a valve, allowing thermactor air to enter exhaust system while preventing exhaust gases from passing in the opposite direction. Air check valve is not interchangeable with pulse air valve.

Air Pump

The 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, which produces carbon monoxide and water.

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 the pump. The by-pass valve performs pressure relief. Air pumps are available in 11 cu. in. and 19 cu. in. sizes. Various drive belt pulley ratios permit a wider range of vehicle applications.

Air Silencer/Filter

The 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 system, or, for a system not using an air supply pump, with impeller-type centrifugal air filter fan.

Air Supply Control Valves

Valves are operated by vacuum to direct air pump output to exhaust manifold or downstream to catalytic converter, depending on system requirements, engine mode and control system.

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

The combination air by-pass and air control valve combines the functions of the by-pass valve and the air control valve into a single unit. There are 2 types of normally closed valves, the non-bleed type and the bleed type, both of which look alike. One distinguishing feature on the bleed type is the percentage of bleed molded into its 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 the other controls thermactor diverter valve. Both valves pass air when deactivated and do not pass air when activated.

Thermactor Idle Vacuum (TIV) Valve

TIV valve vents the vacuum signal to atmosphere when preset manifold vacuum or pressure is exceeded. During periods of extended idle conditions, this valve is used to divert thermactor airflow to limit exhaust temperature, preventing excessive underbody temperature. TIV valve also cuts EGR in a heavy boost mode for turbocharged applications.

EGR SYSTEM

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

Electronic EGR Valve

The Electronic EGR (EEGR) valve is required in EEC-IV systems in which EGR flow is controlled according to computer demands of EGR valve position sensor. The EGR valve is operated by a vacuum signal from EGR electronic vacuum regulator.

EGR Vacuum Regulator (EVR)

The vacuum regulator is an electromagnetic device that controls vacuum output to EGR valve. The EVR is used in place of EGR solenoid vacuum vent valve assembly. Regulator operation is measured as a duty cycle; increased duty is increased vacuum to EGR.

This sensor is attached to the EGR valve assembly and indicates position of EGR valve to the EEC system. It is located on top of the electronic EGR-type valve.

EGR Solenoid Vacuum Vent Valve Assembly

The dual EGR solenoid vacuum vent valve assembly consists of 2 solenoid valves. One is a vacuum vent valve that supplies vacuum to the EGR when energized. The second valve is a vent valve that vents the EGR valve to the atmosphere when de-energized. Both solenoid valves receive variable duty cycle signals from the ECU according to EGR requirements.

EGR Vacuum Control Valve Filter

The EGR vacuum control valve filter is used to vent various emission control components to the atmosphere.

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 system 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 appropriate VACUUM DIAGRAMS article.

Canister Purge Solenoid Valve

Normally closed solenoid valve controls the flow of fuel vapors from canister to intake manifold. Valve is opened or closed by a signal from the ECA during various engine operating modes.

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.

Purge Control Valve

Purge control valve, located in line with carbon canister, controls flow of fuel vapors from carbon canister to intake manifold. Air should not flow through PCV purge line port, unless more than 16 in. Hg is applied to carburetor vacuum port.

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 1.0 in. Hg of vacuum, and 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.

Vacuum Check Valve

A vacuum check valve blocks airflow in one direction, allowing free airflow in the other direction.

Vapor Vent System

System provides a vapor space above gasoline surface in fuel tank. This area is sufficient to permit adequate breathing space for tank vapor valve assembly.

All vapor valves are mounted on fuel tank and use a small orifice that allows only vapor and not liquid fuel to pass into line running to 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 while engine is operating.

POSITIVE CRANKCASE VENTILATION (PCV)

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

Under conditions in which abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), system is designed to allow the excess gases to flow back through crankcase vent hose into the air inlet and be consumed 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 appropriate TESTS W/CODES article in this section.

CHECK ENGINE LIGHT

The CHECK ENGINE light (if equipped) will illuminate when ignition 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 appropriate TESTS W/CODES article in this 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 ECA. The ECA uses this signal to maintain system pressure within the programmed range.

COOLING FAN

The ECA regulates operation of the electric cooling fan through an ECA-controlled relay, which controls the ground circuit or power circuit for the cooling fan. This allows the ECA to operate the cooling fan based on engine temperature. A malfunction of the cooling fan will cause engine overheating and possible detonation.