Modes of Operation

Engine Starting Enrichment
In order to improve starting performance, fuel enrichment during start up is carried out. For a certain time after the engine is started, the air/fuel mixture is enriched slightly in order to stabilize the engine speed. The amount of compensation varies depending on the engine coolant temperature as measured by the Engine Coolant Temperature (ECT) sensor.

Engine Warm-Up Enrichment
When the engine is cold, additional fuel is added in order to ensure good driveability. The level of enrichment of the air/fuel mixture is gradually decreased until the ECT sensor reaches a specified value.

Acceleration Enrichment
During acceleration, the pulse of the fuel injectors is lengthened in order to deliver more fuel. The additional fuel required is relative to the engine coolant temperature. Acceleration Enrichment ensures smooth and reliable engine acceleration.

Power Enrichment
In order to provide maximum power during high engine load driving conditions, the air/fuel mixture is enriched when the throttle valve opening is greater than a specified (PCM determined) value.

System Voltage Compensation
A power supply system voltage drop will delay the mechanical operation of the fuel injector. The actual injector ON time becomes shorter when the system voltage decreases. In order to compensate for this, the fuel injector pulse width signal is lengthened.

Base Air/Fuel Ratio Compensation
The base air/fuel ratio may vary due to differences in individual engines and mileage. In order to compensate for such variations, feedback information is used to adjust the base air/fuel mixture to maintain the optimum air/fuel ratio.

Fuel Cutoff
Fuel injection stops when decelerating (i.e., when the throttle valve is at idle position and the engine speed is high), so that unburned gas will not be exhausted. Fuel injection starts again when the above conditions are no longer present.

Fuel delivery also stops when the engine speed exceeds 6,800 RPM. This will prevent engine overrun which adversely affects the engine. Fuel delivery starts again when the engine speed decreases to less than 6,500 RPM.




Air/Fuel Ratio Feedback Compensation (Closed Loop Operation)
In order to obtain efficient performance of the Three-way Catalytic Converter (TWC) and a high clarification rate of CO, HC and NOx in the exhaust gas stream, the air/fuel mixture must be kept as close to the theoretical air/fuel ratio (14.7:1) as possible. In order to accomplish this the powertrain control module (PCM) first compares the input voltage from the heated oxygen sensor 1 (HO2S 1) with a specified reference voltage. If the HO2S 1 input voltage is higher than the specified reference voltage, the PCM determines that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces the fuel (lean command). If the input voltage from the HO2S 1 is lower than the specified reference voltage, the PCM determines that the air/fuel ratio is leaner and increases the fuel (rich command). By repeating these operations, the PCM can adjust the air/fuel ratio in order to be closer to the theoretical air/fuel ratio. Control of the fuel delivery system as just described is known as Closed Loop operation.

The Closed Loop fuel control operation will not take place under any of the following conditions:
- At engine start up.
- When the fuel injection is increased just after engine start up.
- When the ECT sensor is indicating a low coolant temperature.
- When the engine is operating under a high demand, such as Wide Open Throttle (WOT).
- At fuel cutoff.
- When the HO2S 1 is cold (Open Loop operation).