Computers and Control Systems: Description and Operation

The computerized engine control system is built around an Electronic Control Unit (ECU). The ECU monitors up to 13 inputs and responds with appropriate outputs to manage fuel delivery, ignition timing, and emission control devices. As operating conditions change, the ECU adjusts injector pulse width and ignition timing for optimum performance and fuel economy.
The Throttle Body Fuel Injection System (TBI) controls fuel delivery. This system is a single point, pulse time system that injects fuel through an electrically operated fuel injector into the throttle body above the throttle plate. The fuel injection pulse width, the period of time that the injector is energized causing fuel to be released into the throttle body, is controlled by the ECU.

The ECU has the ability to do a self-diagnosis to check for problem areas within its network. It receives input signals from sensors that react to changing driving conditions, and if these signals are out of range or do not exist, fault codes are generated and stored in its memory. Fault codes can be generated from faulty output devices also, and the ECU can check these using the signals that are sent back via the input sensors.



ECU INPUTS ECU OUTPUTS

^ Start Signal ^ Electric Fuel Pump Relay
^ Engine Coolant Temperature ^ B+ Latch Relay
^ Intake Manifold Air/Fuel Temperature ^ A/C Compressor Clutch Relay
^ Intake Manifold Absolute Pressure ^ Idle Speed Actuator (ISA) Motor
^ Engine Speed (crankshaft position) ^ Ignition Power Module (MPA)
^ Throttle Position ^ Fuel Injector
^ Exhaust Gas Oxygen Content ^ EGR Valve Vacuum Solenoid
^ Battery Voltage ^ Shift Indicator Lamp (Manual Transmission Only)
^ A/C Select & Request
^ Closed Throttle Switch
^ Neutral Safety Switch
^ Power Steering Switch