Air/Fuel Ratio Feedback Compensation-Closed Loop Operation
In order to obtain the most efficient engine performance with a good balance of power and fuel economy, the air/fuel mixture must be kept as close to the theoretical air/fuel ratio of 14.7:1 as possible. Maintaining the 14.7:1 air/fuel ratio also provides efficient operation of the 3-way catalytic converter (TWC) and a high clarification rate of CO, HC and NOx in the exhaust gas stream, In order to accomplish this the PCM first compares the input voltage from the heated oxygen sensor 1 (HO2S 1) with a specified reference voltage.
The HO2S 1 sensor used on the 1.8L-LNK is a typical switching style HO2S. The HO2S input signal is displayed as a voltage within the range of 0-1,200 millivolts. An HO2S value of 400-600 millivolts indicates that the air fuel ratio is near 14.7:1. When 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. 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. 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.
| Air/Fuel Mixture | Exhaust O2 Content | HO2S 1 Output | Fuel System Response |
|---|---|---|---|
| Lean Mixture | High Oxygen | Low Voltage | Rich Command |
| Rich Mixture | Low Oxygen | High Voltage | Lean Command |
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 engine coolant temperature (ECT) sensor is indicating a low coolant temperature.
- When the engine is operating under a high demand, such as at wide open throttle (WOT).
- During fuel cutoff
- When the HO2S 1 is cold-Open Loop operation.
Control of the air supply that is mixed with the metered fuel is detailed in the description of the air intake system. Refer to Air Intake System Description .