System Description

INTRODUCTION
This engine uses a sequential Multi-Port Electronic Fuel Injection system. 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 regulates:
- Ignition timing
- Air/fuel ratio
- Emission control devices
- Cooling fan
- Charging system
- Idle speed
- Vehicle speed control

Various sensors provide the inputs necessary for the PCM to correctly operate these systems. In addition to the sensors, various switches also provide inputs to the PCM.

All inputs to the PCM are converted into signals. The PCM can adapt its programming to meet changing operating conditions.

Fuel is injected into the intake port above the intake valve in precise metered amounts through electrically operated injectors. Under most operating conditions the PCM fires the injectors in a specific sequence, maintaining 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.

The PCM adjusts injector pulse width by opening and closing the ground path to the injector.

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

MODES OF OPERATION
As input signals to the PCM change, the PCM adjusts its response to output devices. For example, the PCM must calculate a different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). There are several different modes of operation that determine how the PCM responds to the various input signals.

OPEN LOOP and CLOSED LOOP Modes
During OPEN LOOP modes the PCM receives input signals and responds according to preset PCM programming. Input from the oxygen (O2S) sensor is not monitored during OPEN LOOP modes.

During CLOSED LOOP modes the PCM does monitor the O2S sensor input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air/fuel ratio of 14.7 parts air to 1 part fuel. By monitoring the exhaust oxygen content through the O2S sensor, the PCM can fine tune the injector pulse width. Fine tuning injector pulse width allows the PCM to achieve optimum fuel economy combined with low emissions.

The multi-port fuel injection system has the following modes of operation:
- Ignition Switch ON (zero RPM)
- Engine Start-up
- Engine Warm-up
- Cruise (Idle)
- Acceleration
- Deceleration
- Wide Open Throttle
- Ignition Switch OFF

The engine start-up (crank), engine warm-up, and wide open throttle modes are OPEN LOOP modes. Under most operating conditions, the acceleration, deceleration, and cruise modes, with the engine at operating temperature are CLOSED LOOP modes.

For more information SEE Engine Control Module.