Modes Of Operation: Notes

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.

There are two different areas of operation, OPEN LOOP and CLOSED LOOP.

During OPEN LOOP modes the PCM receives input signals and responds according to preset PCM programming. Inputs from the upstream and downstream heated oxygen sensors are not monitored during OPEN LOOP modes, except for heated oxygen sensor diagnostics (they are checked for shorted conditions at all times).

During CLOSED LOOP modes the PCM monitors the inputs from the upstream and downstream heated oxygen sensors. The upstream heated oxygen sensor input tells the PCM if the calculated injector pulse width resulted in the ideal air-fuel ratio of 14.7 to one. By monitoring the exhaust oxygen content through the upstream heated oxygen sensor, the PCM can fine tune injector pulse width. Fine tuning injector pulse width allows the PCM to achieve optimum fuel economy combined with low emissions.

For the PCM to enter CLOSED LOOP operation, the following must occur:

1. After the engine is started, the closed loop timer must count down to zero. The engine coolant temperature must be over 0°F for the closed loop timer to initiate. The following start up coolant temperatures are used to determine the closed loop timer start time.
   • If the coolant is over -4°F the PCM will wait 100 seconds.
   • If the coolant is over 14°F the PCM will wait 70 seconds.
   • If the coolant is over 45°F the PCM will wait 45 seconds.
   • If the coolant is over 63°F the PCM will wait 25 seconds.
2. For other temperatures the PCM will interpolate the correct waiting time.
3. O2 sensor voltage must stay below ~1.02 Volts.
4. The engine is NOT in decel fuel shut-off or WOT mode.
5. The engine speed is below 3808 RPM.

The multi-port fuel injection systems 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, deceleration with fuel shutoff and wide open throttle modes are OPEN LOOP modes. Under most operating conditions, the acceleration, deceleration (with A/C on), idle and cruise modes, with the engine at operating temperature  are CLOSED LOOP modes.