General Operation

As input signals to the Powertrain Control Module (PCM) change, The PCM adjusts its response that it sends to the 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). Likewise the PCM changes ignition timing to compensate for different operating conditions. There are nine modes of operation that determine how the PCM responds to the various input signals.

Modes of operation are separated into two different types.

- OPEN LOOP

- CLOSED LOOP

During OPEN LOOP modes the PCM receives input signals and responds only to preset PCM programming. Input from the oxygen (02) sensor is not monitored during OPEN LOOP modes.

During CLOSED LOOP modes the PCM monitors the oxygen 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 of air to 1 part of fuel. By monitoring the exhaust oxygen content, using the oxygen sensor, the PCM can "fine tune" the injector pulse width to achieve optimum fuel economy and performance combined with low emission levels.

The sequential multi-point fuel injection (SFI) system has the following modes of operation:

- Ignition switch ON
- Engine start-up (CRANK)
- Engine warm-up
- Idle/Cruise
- Acceleration
- Deceleration
- Wide Open Throttle (WOT)
- Ignition switch OFF

The ignition switch ON, engine start-up (CRANK), engine warm-up, deceleration, acceleration, wide open throttle, and ignition switch OFF modes are OPEN LOOP modes.

The Cruise and Idle modes, with the engine at operating temperature, are CLOSED LOOP modes.