Modes of Operation

The PCM uses voltage inputs from several sensors to determine how much fuel to give the engine. The fuel is delivered under one of several conditions called modes. All modes are controlled by the PCM.


STARTING MODE
When the ignition is first turned ON (before engaging the starter), the PCM energizes the fuel pump relay for a calibrated time (approximately 2 seconds) allowing the fuel pump to build up pressure. The PCM also checks the Engine Coolant Temperature (ECT) and Throttle Position (TP) sensors to determine the proper air/fuel ratio for starting. This ranges from approximately 0.8:1 at -40°C (-40°F) to 16.8:1 at 110°C (230°F ) engine coolant temperature. The PCM controls the amount of fuel delivered by changing how long the injectors are energized. This is done by pulsing the injectors for very short times.

CLEAR FLOOD MODE
Whenever the engine floods, the engine can be cleared by depressing the accelerator pedal to the floor while cranking the engine. The PCM de-energizes the fuel injectors and holds them de-energized as long as the throttle stays wide open. Whenever the throttle is released to less than 70°, the PCM returns to the starting mode.

ACCELERATION MODE
When the driver depresses on the accelerator pedal, air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the PCM increases the pulse width to the injectors to provide extra fuel during acceleration. The amount of fuel required is based on throttle position, manifold air pressure, and engine speed. A restricted fuel filter or fuel line may cause a DTC P1171 to set during heavy acceleration.

FUEL CUTOFF MODE
To prevent possible engine damage from over-reving, the PCM cuts off fuel from the injectors at a calibrated engine speed, or vehicle speed. On vehicles equipped with automatic transmission, fuel will be shut off if the engine exceeds 4000 RPM in PARK or NEUTRAL. The PCM also cuts off fuel to the fuel injectors at vehicle speeds above 108 mph to prevent tire damage.

DECELERATION MODE
When the driver releases the accelerator pedal, air flow into the engine is reduced. The corresponding changes in throttle position and manifold air pressure are relayed to the PCM, which reduces the injector pulse width to reduce fuel flow. Whenever the deceleration is very rapid, or for long periods (such as long closed throttle coast-down), the PCM shuts OFF fuel completely to protect the catalytic converter.