General System Description

DESCRIPTION
The Powertrain Control Module (PCM) is the control center of the vehicle. It controls the following:

- Fuel metering system.
- Transaxle shifting.
- Emission Systems.
- Ignition timing.

It constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (Service Engine Soon), and store diagnostic trouble codes which identify the problem areas to aid the technician in making repairs.

ALTERNATING SYNCHRONOUS DOUBLE FIRE (ASDF) FUEL INJECTION
For better fuel vaporization and improved emission control, fuel is injected at the intake valves while they are in the closed position. To do this, the fuel injectors are alternately pulsed in pairs. Injectors for cylinders 1 and 4 are electrically paired, as are the injectors for cylinders 2 and 3. Each pair of injectors is pulsed twice (double fire), once on the compression stroke and once on the exhaust stroke for each cylinder.

TRANSAXLE SHIFTING
The Torque Converter Clutch (TCC) system is designed to eliminate power loss by the converter (slippage) thus increasing fuel economy. By locking the converter clutch, a more effective coupling to the flywheel is achieved. The converter clutch is operated by an Powertrain Control Module (PCM) controlled solenoid.

Engagement of the TCC is accomplished by a solenoid operated valve within the transaxle. The solenoid is activated when an internal switch in the PCM is grounded. Although the PCM may command the TCC "ON," the converter clutch will not apply until internal transaxle fluid pressure requirements are met.

EMISSION SYSTEMS

Evaporative Emission (EVAP) Control System
The PCM operates a normally closed solenoid valve, which controls vacuum to the purge valve in the charcoal canister.
The PCM turns "ON" the PWM signal to the solenoid valve to control purge when all conditions for allowing purge are met.

Exhaust Gas Recirculation (EGR) System
To regulate exhaust gas flow, a Powertrain Control Module (PCM) controlled EGR control solenoid valve is used in the vacuum line. The PCM uses information from the following sensors to regulate the solenoid:

- Engine Coolant Temperature (ECT) sensor.
- Throttle Position (TP) sensor.
- Manifold Absolute Pressure (MAP) sensor.
- Vehicle Speed Sensor (VSS).

IGNITION TIMING
The Electronic Ignition (EI) system does not use the conventional distributor and coil. This ignition system consists of two separate ignition coils, an electronic Ignition Control Module (ICM) and a Crankshaft Position (CKP) sensor, related connecting wires and the Ignition Control (IC) portion of the Powertrain Control Module (PCM) make up the remainder of the system.