Modes of Operation

The Control Module monitors the information from several sensors in order to determine the fuel requirements based on the engine operating conditions. The fuel is delivered under one of several conditions called modes. All modes are controlled by the Control Module and are described on the next page.

Starting Mode
When the ignition switch is turned to the ON position, before engaging starter, the Control Module energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The Control Module then checks the Engine Coolant Temperature (ECT) sensor and Throttle Position (TP) sensor in order to determine the proper air and fuel ratio for starting. The Control Module controls the amount of fuel delivered in the starting mode by changing how long the injectors are energized. This is done by pulsing the injectors for very short times.

Clear Flood Mode
If the engine floods, it can be cleared by pushing the accelerator pedal down all the way. The Control Module then completely turns off the fuel. No fuel is delivered from the injectors as long as the throttle stays wide open, and the engine speed is below 600 RPM. If the throttle position becomes less than 80%, the Control Module returns to the starting mode.

Run Mode
The run mode consists of an Open Loop and a Closed Loop operation. When the engine is first started and engine speed is above 400 RPM, the system goes into an Open Loop operation. In Open Loop, the Control Module ignores the signal from the HO2S and calculates the air/fuel ratio based on inputs from the ECT and the Intake Air Temperature (IAT) sensors.

The system stays in an Open Loop until the following conditions are met:

1. The HO2S has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature.)
2. The ECT sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines, and are stored in the Electronically Erasable Programmable Read Only Memory (EEPROM) portion of the Control Module. When these values are met, the system goes into a Closed Loop operation. In a Closed Loop, the Control Module calculates the air and fuel ratio (injector on-time) based on the signal from the HO2S. This allows the air and fuel ratio to stay very close to 14.6:1.

Acceleration Mode
When the driver pushes on the accelerator pedal, the air flow into the cylinders increases rapidly, while the fuel flow tends to lag behind. In order to prevent possible hesitation, the Control Module increases the pulse width to the injectors in order to provide an extra fuel during acceleration. The amount of fuel required is based on throttle position, Mass Air Flow (MAF) sensor, and engine speed.

Fuel Cutoff Mode
In order to prevent possible engine damage from over-speed, the Control Module cuts off fuel from the fuel injectors when the engine speed is above approximately 6500 RPM with the vehicle in any forward gear or reverse, and approximately 3000 RPM in park or neutral on vehicles equipped with automatic transmissions. In order to prevent tire damage, the Control Module also has a fuel cutoff in excess of 108 mph (173 km/h) based on the speed rating of the tires. Fuel is also Cutoff during rapid deceleration. See Deceleration Mode.

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 Control Module, which reduces the injector pulse width, to reduce fuel flow. If decel is very rapid, or for long periods (such as long closed throttle coast-down), the Control Module shuts OFF fuel completely to protect the catalytic converter.

Converter Protection Mode
The Control Module constantly monitors engine operation and estimates conditions that could result in high converter temperatures. If the Control Module determines the converter may overheat, it causes the system to return to Open Loop operation and enriches the fuel mixture.

Battery Voltage Correction Mode
When battery voltage is low, the control module can compensate for a weak spark delivered to the distributor by increasing the following items:

- The injector ON time.
- The idle RPM.
- The ignition dwell time.