General System Description

Fig. 1 Powertrain Control Module:

GENERAL INFORMATION
This vehicle uses a sequential Multi-Port Electronic Fuel Injection system (MPI). The MPI system is computer regulated and provides precise air/fuel ratios for all driving conditions. The powertrain control module (PCM) operates the fuel injection system.

The PCM Controls:
- Ignition Timing
- Air-fuel Ratio
- Emission Control Devices
- Cooling Fan
- Charging System
- Idle Speed
- Speed Control

Various sensors and switches provide the inputs necessary for the PCM to correctly operate these systems.
- All sensor and switch inputs to the PCM are converted into signals.

The PCM can adapt its programming to meet changing operating conditions.

Fuel Injection
Fuel is injected into the intake port above the intake valve in precise metered amounts through electrically operated injectors.
- The PCM fires the injectors in a specific sequence by opening and closing the injector ground paths.
- Under most operating conditions, the PCM maintains an air fuel ratio of 14.7 parts air to 1 part fuel by constantly adjusting injector pulse width.
- Injector pulse width is the length of time the injector is open.

NOTE: Engine RPM (speed) and manifold absolute pressure (air density) are the primary inputs that determine injector pulse width.

Fig. 2 Data Link (Diagnostic) Connector:

The Powertrain Control Module (PCM) is a digital computer containing a microprocessor (Fig. 1). The PCM receives input signals from various switches and sensors that are referred to as PCM Inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices that are referred to as PCM Outputs.

PCM Inputs:
- Air Conditioning Controls
- Battery Voltage
- Battery Temperature Sensor
- Brake Switch
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Engine Coolant Temperature Sensor
- Fuel Level Sensor
- Ignition Switch
- Intake Air Temperature Sensor
- Knock Sensor
- Manifold Absolute Pressure (MAP) Sensor
- Oxygen Sensors
- Power Steering Pressure Switch
- SCI Receiver
- Speed Control Switches
- Throttle Position Sensor
- Transmission Park/Neutral Switch (Automatic Transmission)
- Vehicle Speed Sensor

PCM Outputs:
- Air Conditioning Clutch Relay
- Auto Shutdown (ASD) Relay
- Charging Indicator Lamp
- SCI Transmit
- Duty Cycle EVAP Canister Purge Solenoid
- EGR Solenoid
- Fuel Injectors
- Fuel Pump Relay
- Generator Field
- Idle Air Control Motor
- Ignition Coils
- Malfunction Indicator (Check Engine) Lamp
- Radiator Fan Relays
- Speed Control Solenoids

Based on inputs it receives, the PCM adjusts:
- Fuel Injector Pulse Width
- Idle Speed
- Ignition Spark Advance
- Ignition Coil Dwell
- EVAP Canister Purge Operation.

The PCM Regulates:
- Cooling Fan
- Air Conditioning
- Speed Control System
- Generator Charge Rate -- by Adjusting The Generator Field

The PCM Also Performs Diagnostics See On-Board Diagnostic System On-Board Diagnostic System

The PCM adjusts injector pulse width (air-fuel ratio) based on:
- Battery Voltage
- Coolant Temperature
- Exhaust Gas Content (Oxygen Sensor)
- Engine Speed (Crankshaft Position Sensor)
- Intake Air Temperature
- Manifold Absolute Pressure
- Throttle Position

The PCM adjusts ignition timing based on:
- Coolant Temperature
- Engine Speed (Crankshaft Position Sensor)
- Knock Sensor
- Manifold Absolute Pressure
- Throttle Position
- Transmission Gear Selection (Park/Neutral Switch)
- Intake Air Temperature

The PCM also adjusts engine idle speed through the idle air control motor based on:
- Air Conditioning Sense
- Battery Voltage
- Battery Temperature
- Brake Switch
- Coolant Temperature
- Engine Speed (Crankshaft Position Sensor)
- Engine Run Time
- Manifold Absolute Pressure
- Power Steering Pressure Switch
- Throttle Position
- Transmission Gear Selection (Park/Neutral Switch)
- Vehicle Distance (Speed)

ASD and Fuel Pump Relay Control
The Auto Shutdown (ASD) and fuel pump relays are mounted externally, but turned on and off by the PCM.

Crankshaft Position (Engine Speed) Signal
The crankshaft position sensor signal is sent to the PCM. If the PCM does not receive the signal within approximately one second of engine cranking, it deactivates the ASD relay and fuel pump relay When these relays deactivate, power is shut off from the fuel injectors, ignition coils, heating element in the oxygen sensors and the fuel pump.

PCM Regulated Output Supply Voltages
The PCM contains a voltage converter that changes battery voltage to a regulated 9 volts direct current to power:
- Camshaft Position Sensor
- Crankshaft Position Sensor
- Vehicle Speed Sensor

The PCM also provides a 5 volt direct current supply for:
- Manifold Absolute Pressure Sensor
- Throttle Position Sensor