Engine Start-Up (Cranking)

THE PCM LOOKS FOR AN IGNITION REFENCE SIGNAL:
If a signal is received within 0.5 seconds, the PCM energizes (grounds), the Automatic Shut Down (ASD) and fuel pump relays. Supplying battery voltage to the fuel pump, fuel injector, ignition coil and oxygen sensor heating element. After the PCM energizes the ASD and fuel pump relays, the PCM fires the fuel injector 4 times per revolution, (instead of the normal 2 pulses per revolution).

If NO signal received within 0.5 seconds, the PCM does not energize the ASD and fuel pump relays.

PCM MONITORS:
- Engine Temperature (ECT Sensor)
- Manifold Vacuum (MAP Sensor)
- Throttle Position (TPS)
- Engine speed (distributor pick-up)

PCM CONTROLS:
- Injector pulse width, (switching the ground on and off twice per engine revolution).
- Idle speed, through the idle air control motor.
- Ignition timing.

PCM TESTS MAP SENSOR OPERATION:
When engine idle comes within ±64 rpm of target idle speed, the PCM, compares the current MAP sensor reading to the atmospheric pressure measurement, taken during Ignition ON (Zero RPM) mode, and if a minimum difference is not detected, a MAP sensor Diagnostic Trouble Code (DTC) is set in memory.