Engine Controls - Theory & Operation - Eec-Iv: Other Lincoln Mark I

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.

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.

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 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, intercooler, knock sensor, knock control unit, overboost warning device and vane air temperature sensor. 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. This allows a denser air/fuel charge to enter combustion chamber and improve efficiency.

Integrated Relay Control Module (IRCM)

IRCM interfaces with the ECA to control cooling fan, A/C clutch and fuel pump operation. The IRCM also incorporates electronic engine control power relay to supply power to the EEC-IV system.

INTEGRATED RELAY CONTROL MODULE (IRCM) 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 WIRING DIAGRAMS article in the ENGINE PERFORMANCE 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

BP 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, EGR flow and spark advance.

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

Brake On-Off (BOO) Switch

BOO switch is mounted on the brake pedal. It signals the ECA of conditions requiring air/fuel ratio adjustment.

Camshaft Sensor

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 during engine start-up for ECA to initiate correct firing order.

Clutch Engage Switch

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

Coolant Temperature Sensor

See ENGINE COOLANT TEMPERATURE (ECT) SENSOR.

Crankshaft Angle Sensor

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.

Delta 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 ECA where it is translated and used to compute correct EGR flow.

EGR Valve Position (EVP) Sensor

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

ECT sensor inputs 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. Ignition Timing

Heated Exhaust Gas Oxygen (HEGO) Sensor

HEGO sensor monitors oxygen content of exhaust gases. This electrically heated O2 sensor is mounted in the exhaust manifold. When HEGO 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 Probe 3.0L engine, all V6 and V8 engines are equipped with 2 sensors, one for each exhaust bank.

Knock Sensor (KS)

KS measures vibrations (pre-ignition) 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 ECA monitors signal from KCU and adjusts ignition timing if pre-ignition occurs. The KS is threaded into the engine block, near the oil pressure switch.

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 ECA.

The MAP sensor uses frequency to measure 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.

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 measured as it passes over the cold wire sensor. The ECA uses this information to control fuel delivery.

Neutral Gear Switch (NGS)

NGS monitors transmission gear selection and signals the ECA. This signal affects air/fuel ratio, idle speed and ignition timing.

Power Steering (P/S) Pressure Switch

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

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

The 6-pin STO connector 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)

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

Vehicle Speed Sensor (VSS)

VSS is mounted in transmission/transaxle. The VSS generates electrical pulses when vehicle is in motion. The electrical pulses are sent to the ECA where they are translated and used to compute vehicle speed. The ECA interprets VSS input along with throttle position sensor input.

ECA differentiates between closed throttle deceleration and closed throttle idle (vehicle stopped) conditions. During deceleration, ECA controls By-Pass Air Control (BAC) valve to maintain a desired manifold pressure value. During idle (vehicle stopped), ECA controls Idle Speed Control (ISC) motor to maintain a correct idle speed.

OUTPUT SIGNALS

Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

A/C Clutch Cycling Pressure Switch

See MISCELLANEOUS CONTROLS .

By-Pass Air Control (BAC) Valve

See IDLE SPEED under FUEL SYSTEM.

Canister Purge Solenoid Valve

See EMISSION SYSTEMS .

CHECK ENGINE Light

See SELF-DIAGNOSTIC SYSTEM .

Cooling Fan

See MISCELLANEOUS CONTROLS .

EGR System

See EMISSION SYSTEMS.

Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM.

Fuel Pressure Regulator

See FUEL DELIVERY under FUEL SYSTEM.

Fuel Pump

See FUEL DELIVERY under FUEL SYSTEM.

Self-Diagnostic

See SELF-DIAGNOSTIC SYSTEM.

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 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 stream. 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.

Fuel Pump Shutoff (Inertia) Switch

In the event of a collision or vehicle roll-over, 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 re-start the vehicle unless the switch is reset. A reset button is located on the switch assembly.

The ECA controls fuel injector ON time to meter fuel quantity into intake ports. The ECA 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 ECA-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.

BAC valve, mounted on the throttle body, controls idle quality 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 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 ECA.

DISTRIBUTORLESS IGNITION SYSTEMS (1.9L & 4.6L)

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. Also, the module generates an Ignition Diagnostic Monitor (IDM) signal to ECA, which is used to provide a tach output signal and indicate a failure mode if detected.

The VRS 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 ECA to identify crankshaft position and initiate correct firing order.

The EDIS module is a microprocessor with coil drivers. EDIS Module strategy controls 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, and 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 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

DISTRIBUTORLESS IGNITION SYSTEMS (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 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 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 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 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 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 DIS module to the ECA which 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 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 driveable 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.

DISTRIBUTORLESS IGN SYSTEM (3.0L SHO & 3.8L SUPERCHARGED)

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 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.

The Cylinder Identification (CID) signal is generated by Hall Effect camshaft 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 which 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 (TFI-IV)

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. The TFI module may be mounted in the base of the distributor bowl or on the cowl behind engine.

TFI systems use Hall Effect 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 coil secondary voltage. Dwell is controlled by TFI module on some models and by ECA on others.

Distributors that do not contain TFI module are called Closed Bowl Distributor (CBD) systems. 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 systems.

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 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. May be one-way or two-way valves 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 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

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 to the exhaust manifold or underbody catalytic converter. Some models may use a combined air by-pass/air control valve.

Anti-Backfire (Gulp) Valve

GULP 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 one-way check valve, allowing thermactor air to enter exhaust system while preventing exhaust gases from passing in the opposite direction. The air check valve is not interchangeable with pulse air valve.

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 pulley 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.

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

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

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.

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 sensor. The EGR valve is operated by a vacuum signal from EGR electronic vacuum regulator.

EGR Vacuum Regulator (EVR)

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

EVP 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 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 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.

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.

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 are purged into engine during operation.

POSITIVE CRANKCASE VENTILATION (PCV)

PCV system uses intake manifold vacuum to recycle blow-by vapors from the crankcase to the combustion chamber, where they are burned. PCV valve meters flow of blow-by vapors, according to manifold vacuum.

When high amounts of blow-by gases are produced (such as worn piston rings), excess gases flow back through crankcase vent hose into the air inlet and are burned during normal combustion.

The CHECK ENGINE light 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 appropriate G - EEC IV TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

A/C CLUTCH CYCLING PRESSURE SWITCH (CCPS)

On models with manual A/C system, the CCPS is mounted on top of the receiver-drier. Based on refrigerant system pressure, a signal is sent to the ECA. The ECA uses this signal to maintain system pressure within the programmed range.

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.