Modes of Operation

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

STARTING MODE
When the ignition is first turned to the On position, the PCM turns on the fuel pump relay for two seconds, allowing the fuel pump to build pressure. The PCM also checks the engine coolant temperature (ECT) sensor and throttle position (TP) sensor, to determine the proper air/fuel ratio for starting. This ranges from approximately 0.8:1 at -40°C (-40°F) to 14.6:1 at 104°C (220°F) engine coolant temperature.

CLEAR FLOOD MODE
If the engine floods, it may be cleared by pressing the accelerator pedal all the way to the floor. The PCM then completely turns off the fuel. The PCM holds this fuel injector rate as long as the throttle stays wide open, and the engine speed is below approximately 400 rpm. If the throttle position becomes less than approximately 75 percent, the PCM returns to the starting mode.

RUN MODE
The run mode has two conditions, called Open Loop and Closed Loop:

Open Loop
When the engine is first started, and engine speed is above 400 RPM, the system goes into Open Loop operation. The PCM ignores the signal from the oxygen sensor, and calculates the fuel required based on inputs from the engine coolant temperature (ECT) and manifold absolute pressure (MAP) sensors. The system stays in open loop until the following conditions are met:
1. The oxygen sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature.)
2. The engine coolant temperature (ECT) sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting the engine.

Closed Loop
Specific values for the above conditions exist and are stored in the memory calibration module. When these values are met, the system goes into Closed Loop operation. In closed loop, the PCM calculates the fuel required in the same manner as open loop but corrects for small errors based on the signal from the oxygen sensor. This allows the air/fuel ratio to stay very close to 14.7:1. The best mixture to minimize exhaust emissions is 14.7:1 air/fuel ratio, which allows the three way catalytic converter to operate most efficiently. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a closed loop system.

ACCELERATION MODE
The PCM responds to rapid increases in throttle position and manifold pressure, providing extra fuel needed for smooth acceleration.

DECELERATION MODE
The PCM responds to decreases in throttle position and manifold pressure reducing the amount of fuel. When deceleration is extended, the PCM cuts-off fuel completely when power is not needed.

BATTERY VOLTAGE CORRECTION MODE
When battery voltage is low, the PCM compensates by:
^ Increasing the fuel injector pulse width to provide proper fuel.
^ Increasing the engine idle rpm to increase generator output.

FUEL CUT-OFF MODE
To prevent possible engine damage from overspeed, the PCM cuts-off fuel from the fuel injectors when engine speed is above the following rpm:
SOHC (L24) Auto Trans. 5750 ± 150
SOHC (L24) Manual Trans. 6000 ± 150
DOHC (LL0) Auto/Manual Trans. 6750 ± 150

In neutral or while stopped, the engine speed is limited to 4000 rpm.