For 1990-2009 cars

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 the throttle position, the manifold air pressure, and the 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-revving, the PCM cuts off fuel from the injectors at a calibrated engine speed, or vehicle speed. On vehicles equipped with an 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 in order to prevent tire damage.

### Deceleration Mode

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

#### Battery Voltage Correction Mode

When battery voltage is low, a DTC P0562 may be set and the PCM will compensates for the weak spark delivered by the electronic ignition system by:

• | Increasing the injector pulse width.

• | Increasing the idle RPM.

• | Increasing ignition dwell time.

### 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 637 RPM, the system goes into Open Loop operation. Also, when the engine is first started and the throttle position has not changed, the system remains in Open Loop until the throttle is moved. When the system is in Open Loop operation, the PCM ignores the signal from the O2S and calculates the air/fuel ratio 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:

• | The O2S has varying voltage output, showing that the O2S is hot enough to operate properly. This depends on temperature.

• | The ECT sensor is above a specified temperature.

### Closed Loop

Specific values for the above conditions exist for each different engine, and are stored in the Electronically Erasable Programmable Read Only Memory (EEPROM). When these values are met, the system goes into Closed Loop operation. The PCM calculates the air/fuel ratio (injector on-time) based on the signal from the O2S. This allows the air/fuel ratio to stay very close to 14.6:1.