The Electronic Control Assembly (ECA) is a solid-state micro-computer consisting of a processor assembly and a calibration assembly. It is located under the instrument panel or passenger's seat and is usually covered by a kick panel. 1981-82 models use an EEC-III engine control system, while 1983 and later models use EEC-IV. Although the two systems are similar in appearance and operation, the ECA units are not interchangeable. A multi-pin connector links the ECA with all system components. The processor assembly is housed in an aluminum case. It contains circuits designed to continuously sample input signals from the engine sensors. It then calculates and sends out proper control signals to adjust air/fuel ratio, spark timing and emission system operation. The processor also provides a continuous reference voltage to the B/MAP, EVP and TPS sensors. EEC-III reference voltage is 8-10 volts, while EEC-IV systems use a 5-volt reference signal. The calibration assembly is contained in a black plastic housing which plugs into the top of the processor assembly. It contains the memory and programming information used by the processor to determine optimum operating conditions. Different calibration information is used in different vehicle applications, such as California or Federal models. For this reason, careful identification of the engine, year, model and type of electronic control system is essential to insure correct component replacement.
Air Charge Temperature Sensor (ACT)
The ACT is threaded into the intake manifold air runner. It is located behind the distributor on V6 engines and directly below the accelerator linkage on V8 engines. The ACT monitors air/fuel charge temperature and sends an appropriate signal to the ECA. This information is used to correct fuel enrichment for variations in intake air density due to temperature changes.Barometric & Manifold Absolute Pressure Sensors (B/MAP)
The B/MAP sensor on V8 engines is located on the right fender panel in the engine compartment. The MAP sensor used on V6 engines is separate from the barometric sensor and is located on the left fender panel in the engine compartment. The barometric sensor signals the ECA of changes in atmospheric pressure and density to regulate calculated air flow into the engine. The MAP sensor monitors and signals the ECA of changes in intake manifold pressure which result from engine load, speed and atmospheric pressure changes.Crankshaft Position (CP) Sensor
The purpose of the CP sensor is to provide the ECA with an accurate ignition timing reference (when the piston reaches 10º BTDC) and injector operation information (twice each crankshaft revolution). The crankshaft vibration damper is fitted with a 4-lobe pulse ring. As the crankshaft rotates, the pulse ring lobes interrupt the magnetic field at the tip of the CP sensor.EGR Valve Position Sensor (EVP)
This sensor, mounted on EGR valve, signals the computer of EGR opening so that it may subtract EGR flow from total air flow into the manifold. In this way, EGR flow is excluded from air flow information used to determine mixture requirements.Engine Coolant Temperature Sensor (ECT)
The ECT is threaded into the intake manifold water jacket directly above the water pump bypass hose. The ECT monitors coolant temperature and signals the ECA, which then uses these signals for mixture enrichment (during cool operation), ignition timing and EGR operation. The resistance value of the ECT increases with temperature, causing a voltage signal drop as the engine warms up.Exhaust Gas Oxygen Sensor (EGO)
The EGO is mounted in the right side exhaust manifold on V8 engines, in the left and right side exhaust manifolds on V6 models. The EGO monitors oxygen content of exhaust gases and sends a constantly changing voltage signal to the ECA. The ECA analyzes this signal and adjusts the air/fuel mixture to obtain the optimum (stoichiometric) ratio.Knock Sensor (KS)
This sensor is used on various models equipped with the V6 engine. It is attached to the intake manifold in front of the ACT sensor. The KS detects engine vibrations caused by preignition or detonation and provides information to the ECA, which then retards the timing to eliminate detonation.Thick Film Integrated Module Sensor (TFI)
The TFI module sensor plugs into the distributor just below the distributor cap and replaces the CP sensor on some engines. Its function is to provide the ECA with ignition timing information, similar to what the CP sensor provides.Throttle Position Sensor (TPS)
The TPS is mounted on the right side of the throttle body, directly connected to the throttle shaft. The TPS senses the throttle movement and position, and transmits an appropriate electrical signal to the ECA. These signals are used by the ECA to adjust the air/fuel mixture, spark timing and EGR operation according to engine load at idle, part throttle, or full throttle. The TPS is nonadjustable.
CFI COMPONENT TESTING
Diagnostic and test procedures on the EEC-III and EEC-IV electronic control systems require the use of special test equipment. Have these systems tested professionally.
Before beginning any component testing, always check the following:
Solenoid and Sensor Resistance Tests
All CFI components must be disconnected from the circuit before testing the resistance with a suitable ohmmeter. Replace any component whose measured resistance does not agree with the specifications chart. Shorting the wiring harness across a solenoid valve can burn out the circuitry in the ECA that controls the solenoid valve actuator. Exercise caution when testing the solenoid valves to avoid accidental damage to the ECA.