DESCRIPTION
The center of the EEC-IV system is the Electronic Control Assembly (ECA). The ECA receives information from various sensors and switches. Based on information received and the operation program in the ECA's memory, the ECA generates output signals to control engine operation.
The calibration module for EEC-IV system is mounted inside the ECA. The ECA is located in the passenger compartment, in one of the following locations: under center console, under dash on left side of steering column, under passenger seat, or under dash behind right kick panel.
The EEC-IV system controls 3 major areas of engine operation: Air/fuel mixture, ignition, and emission control. Additionally, the system can control A/C compressor clutch operation and idle speed. The system provides self-diagnostic capabilities.
All models with 3.8L and 5.0L engines that are equipped with fuel injection use a central fuel injection (CFI). CFI systems use a central throttle body with either 1 or 2 injectors in the throttle body.
The ignition system is controlled by the ECA through a Thick Film Ignition (TFI-IV) module. Ignition timing (advance or retard) and dwell are controlled with this system to improve ignition system performance. The ignition coil is an "E-Core" version and replaces the earlier oil filled coil.
Emission control components controlled by this system include EGR and canister purge. These systems are normally off, but are turned on when the engine is ready to operate with the mixture change caused by EGR and canister purge operation.
The engine control system consists of the ECA, sensors and switches, and actuators. In order for the ECA to perform its function properly, it must be kept constantly informed of engine operating conditions.
It is the task of the engine sensors to supply the ECA, via electrical signals, with specific information required to determine engine operating conditions. The ECA will then send out electrical signals to control air/fuel ratio, emission controls, idle speed and ignition timing. Individual component operation is as follows
A/C Compressor Clutch Signal
Whenever battery voltage is applied to compressor clutch, a signal is sent to ECA. ECA uses signal to increase engine idle speed to compensate for added load created by A/C compressor. Idle speed is increased by using throttle air by-pass valve on 1.6L and 2.3L EFI models, throttle kicker solenoid on 5.0L models, and idle speed control motor on all other models.
Air Charge Temperature (ACT) Sensor (2.3L HSC, 3.8L & 5.0L Models)
The ACT is threaded into cylinder runner of intake manifold or attached to air cleaner. ACT provides ECA with air-fuel mixture temperature information. THe ECA uses this information for correcting fuel flow and to control fuel flow during cold enrichment (cold starts).
Airflow Meter Assembly (VAF & VAT Sensors)(1.6L & 2.3L EFI/Turbo Models)
The airflow meter housing incorporates 2 sensors and is mounted between the air cleaner and the throttle body assembly. The vane airflow (VAF) sensor measures the volume of air drawn into engine and relays this information to the ECA by means of a potentiometer attached to the vane assembly. The vane air temperature (VAT) sensor continually measures intake air temperature and sends this information to the ECA.
Barometric Pressure Sensor (BPS)
Sensor is mounted on right inner fender and measures barometric pressure of atmospheric air on 1.6L and 2.3L EFI/Turbo models. Signals are converted to electrical signals and sent to ECA. ECA uses this signal to calculate correct fuel flow for altitude compensation.
EGR Valve Position Sensor (EVP)(2.3L HSC, 3.8L & 5.0L Engines)
This sensor is located on top of the EGR valve. It tells the ECA the position of the EGR valve.
Engine Coolant Temperature (ECT) Sensor
This sensor, threaded into heater supply tube, monitors engine coolant temperature. The ECA is sent a signal throughout the entire range of operating temperatures. This influences ECA control of fuel mixture enrichment, ignition timing, and EGR operation. On models equipped with electronic instrument cluster, ECT output is also used to control coolant temperature indicator lamp.
Manifold Absolute Pressure (MAP) Sensor (2.3L HSC, 2.3L OHC, 3.8L & 5.0L Engines)
MAP sensor measures absolute pressure of mixture in intake manifold and sends a signal to ECA that is proportional to absolute pressure. It is mounted on right inner fender for 5.0L engine and left inner fender for all others.
Oxygen (EGO) Sensor
This sensor is threaded into exhaust manifold where it constantly monitors oxygen content of exhaust gases. A voltage signal is produced which varies according to difference in oxygen content between exhaust gases and surrounding atmosphere.
This signal is sent to the ECA which translates exhaust gas oxygen content to air/fuel ratio. It then alters air/fuel ratio to hold the ideal ratio for current engine operating conditions.
Profile Ignition Pick-Up (PIP)
The PIP informs the ECA of crankshaft position and speed. PIP assembly is integral with distributor on all models. PIP has an armature with 4 windows and 4 metal tabs that rotate past a stator assembly (Hall effect switch). Ignition distributor does not have any mechanical or vacuum advance. Distributor is adjustable for resetting base timing if necessary.
Self-Test Input
Self-test input is a wire (pigtail) near self-test connector used to activate the Quick Test. Self-test procedures are built into EEC-IV control module so system can display continuous self-test codes for diagnosis of intermittent problems.
Throttle Position Sensor (TPS)
The TPS is mounted on side of throttle body and connected directly to throttle shaft. The TPS senses throttle movement and position and then transmits an electrical signal to the ECA. These signals keep the ECA informed of wide open throttle, closed throttle, or normal cruise conditions.
A/C & Fan Controller Module
A/C and Cooling Fan Controller Module is operated by ECA, coolant temperature switch and brake/stop light switch. Controller module provides an output signal which controls operation of A/C compressor clutch and engine cooling fan.
EEC Power Relay
This relay is activated by ignition switch. Relay supplies battery voltage to ECA when switch is on. Some power relays incorporate a time delay of 5-10 seconds. If time delay is used, a throttle control activator assembly is also used.
Canister Purge Solenoid (CANP)
This solenoid switches manifold vacuum to operate canister purge valve when a signal is received from ECA. Vacuum opens purge valve when solenoid is energized.
EGR Control Solenoid
Solenoid switches manifold vacuum to operate EGR valve on command from ECA. Vacuum opens the EGR valve when the solenoid is energized.
EGR Shut-Off Solenoid
EGR shut-off solenoid is an electrically-operated vacuum valve located between manifold vacuum source and EGR valve. A controlled vacuum bleed is located between solenoid and EGR valve. This vacuum bleed is a Backpressure Variable Transducer. These 2 devices operate EGR valve for optimum performance. Solenoid switched vacuum is also supplied to canister purge valve.
EGR Vent Solenoid
Solenoid vents EGR control solenoid vacuum line. When vent solenoid is energized, control solenoid can open EGR valve.
Exhaust Heat Control Valve
This valve diverts hot exhaust manifold gases to intake manifold riser pad to heat incoming air/fuel mixture. The ECA monitors coolant temperature and engine load to control operation of this valve. This valve is used on all 3.8L engines and may be used on 5.0L engine.
Fuel Injectors
On 3.8L and 5.0L engines, 2 solenoid-operated injectors are used inside the throttle body. On all fuel injected models, ECA controls length of time each injector is open. The "open" time of injector governs amount of fuel delivered.
Fuel Pump Relay (Fuel Injected Models)
Fuel pump relay is activated by ECA with ignition switch in "ON" or "CRANK" positions. When ignition switch is turned to "ON" position, relay is activated to supply initial line pressure to system.
Idle Speed Control (ISC) Motor
This is a DC motor used to provide idle speed control according to signals from ECA.
Self-Test Output
Part of the self-test connector, service codes are transmitted through the output in the form of timed pulses. These pulses are read as diagnostic codes.
Thermactor Air By-Pass (TAB) Solenoid
Solenoid provides a vacuum signal to by-pass valve in response to ECA signals. The TAB valve then by-passes thermactor pump air to atmosphere.
Thermactor Air Diverter (TAD) Solenoid
Solenoid provides a vacuum signal to diverter valve in response to ECA signals. The TAD valve then diverts thermactor pump air to either exhaust manifold or catalytic converter.
TFI Module
The TFI module triggers ignition coil and determines dwell. Module is mounted on side of distributor. ECA uses signal from Profile Ignition Pick-Up to determine crankshaft position. Ignition timing is determined by ECA, which then signals TFI module to fire coil.
Throttle Kicker Solenoid
Two-port valve with an atmospheric vent. A vacuum diaphragm is used to maintain nominal idle speed on command from ECA.
Wide Open Throttle (WOT) A/C Cut-Out
This circuit is energized by ECA when WOT condition is detected. During WOT, power to the A/C compressor clutch is disconnected until after partial throttle operation resumes.