Ignition Switch On (Engine Off) Mode

When ignition switch activates fuel injection system, following actions occur:

1. The PCM determines atmospheric air pressure from MAP sensor input to determine basic fuel strategy.
2. The PCM monitors engine coolant temperature sensor and throttle position sensor input. The PCM modifies fuel strategy based on this input.

When ignition key is in "on" position and engine is not running (zero rpm), auto shutdown relay and fuel pump relay are not energized. Therefore, voltage is not supplied to fuel pump, ignition coil, and fuel injectors.

Engine Start-Up Mode  - This is an open loop mode. The following actions occur when starter motor is engaged:

1. The auto shutdown and fuel pump relays are energized. If PCM does not receive camshaft and crankshaft signal within approximately one second, these relays are de-energized.
2. The PCM energizes all fuel injectors until it determines crankshaft position from camshaft and crankshaft signals. The PCM determines crankshaft position within one engine revolution. After crankshaft position has been determined, PCM energizes fuel injectors in sequence. The PCM adjusts injector pulse width and synchronizes fuel injectors by controlling fuel injectors' ground paths.

Once auto shutdown and fuel pump relays have been energized, PCM determines fuel injector pulse width based on following:

• Engine Coolant Temperature
• Manifold Absolute Pressure
• Intake Air Temperature
• Engine Revolutions
• Throttle Position

The PCM determines spark advance based on following:

• Engine Coolant Temperature
• Crankshaft Position
• Camshaft Position
• Intake Air Temperature
• Manifold Absolute Pressure
• Throttle Position

Engine Warm-Up Mode  - This is an open loop mode. The PCM adjusts injector pulse width and controls injector synchronization by controlling fuel injectors' ground paths. The PCM adjusts ignition timing and engine idle speed. The PCM adjusts idle speed by controlling idle air control motor.

Cruise or Idle Mode  - When engine is at normal operating temperature, this is a closed loop mode. During certain idle conditions, PCM may enter into a variable idle speed strategy. At this time, PCM adjusts engine speed based on following inputs:

• Throttle Position
• Battery Voltage
• Engine Coolant Temperature

Acceleration Mode  - This is a closed loop mode. The PCM recognizes an increase in throttle position and a decrease in Manifold Vacuum as engine load increases. In response, PCM increases injector pulse width to meet increased load.

Deceleration Mode  - This is a closed loop mode. The PCM recognizes a decrease in throttle position and an increase in Manifold Vacuum as engine load decreases. In response, PCM decreases injector pulse width to meet decreased load.

Wide Open Throttle Mode  - This is an open loop mode. The throttle position sensor notifies PCM of a wide open throttle condition. The PCM adjusts injector pulse width to supply a predetermined amount of additional fuel.