Air/Fuel Ratio Feedback Compensation (Closed Loop Operation)
In order to obtain efficient performance of the 3-way catalytic converter 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 of 14.7:1 as possible. 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. 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. 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. See CLOSED LOOP FUEL CONTROL OPERATION table.
| 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).