Computers and Control Systems: Description and Operation

Fig. 1 Component locations. EEC III:

This system, Fig. 1, used on some 1983 vehicles, provides a more complete monitoring and control of engine operating functions than is possible with mechanically operated systems. The system affects emissions, fuel economy, and driveability through the use of various sensors and actuators. Ignition, fuel metering, EGR, as well as auxiliary functions including Thermactor air flow, canister purge, and throttle kicker are controlled by the system.
The engine is equipped with seven sensors which monitor the following: 1) Crankshaft position, 2) EGR valve position, 3) Throttle position, 4) Barometric pressure, 5) Manifold absolute pressure, 6) Engine coolant temperature, and 7) Oxygen content of the exhaust gases.
The sensors continuously monitor and transmit information to the Electronic Control Assembly (ECA) for evaluation. The ECA then computes the correct operating mode. During the various operating modes, the ECA sends output signals to:
a. The ignition module to adjust timing and duty cycle.
b. The feedback carburetor to adjust the air/fuel ratio.
c. The EGR control solenoids to adjust EGR flow rate.
d. The Thermactor air control solenoids to direct the Thermactor air flow.
e. The canister purge solenoid to control fuel vapor flow.
f. The throttle kicker solenoid to adjust engine idle speed.




SYSTEM OPERATING STRATEGIES

The system is designed to operate using three operating strategies: 1) Base engine strategy, 2) Modulator strategy and 3) Limited operational strategy (LOS).
The base engine strategy is used under certain operating conditions encountered during normal driving. To control the system in the wide range of conditions found during normal driving, the base engine strategy is divided into four sub-modes: 1) Crank mode, 2) Closed throttle mode, 3) Part throttle mode and 4) Wide open throttle mode. The ECA determines the proper mode according to the information supplied by the sensors. The ECA then operates accordingly to control the system actuators according to calibration of the engine.
The modulator strategy is used during uncommon operating conditions such as cold or extremely hot engine operation or high altitude operation, etc. The modulator strategy changes the base engine strategy to compensate for these conditions.
The limited operational strategy is used when a failure within the ECA occurs, and allows safe vehicle operation and prevents component damage. During the LOS mode, reduced engine performance may be encountered. If this condition should be encountered, the vehicle should be serviced immediately to prevent minimal operation in the LOS mode. In the LOS modes, the output signals are cut off to: 1) EGR control solenoids, 2) Thermactor air control solenoids, 3) Canister purge and 4) Throttle kicker solenoid. Additionally, the spark advance at the crankshaft becomes 10° BTDC regardless of sensor inputs. Also, two windings of the Feedback Carburetor Actuator are energized to maintain the air/fuel ratio setting as it was before entering the LOS mode.