Air/Fuel Ratio Feedback Compensation

DESCRIPTION
It is necessary to keep the air/fuel mixture close to the theoretical air/fuel ratio (14.7:1) to obtain efficient performance of the three way catalyst and high clarification rate of CO, HC and NOx in the exhaust gas.

OPERATION
The Powertrain Control Module (PCM) operates as follows. First, it compares the input from the Heated Oxygen Sensor 1 (HO2S 1) with a specified reference voltage, and if the input is higher, it detects that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces fuel. If the input is lower, it detects that the air/fuel ratio is leaner and increases fuel. By repeating these operations, it adjusts the air/fuel ratio closer to the theoretical air/fuel ratio.

1. When oxygen concentration in the exhaust gas is low; that is, when the air/fuel ratio is smaller than the theoretical air/fuel ratio (fuel is richer), electromotive force of the HO2S 1 increases and a rich signal is sent to the PCM.
2. Upon receipt of the rich signal, the PCM decreases the amount of fuel injection, which causes oxygen concentration in the exhaust gas to increase and electromotive force of the HO2S 1 to decrease, then a lean signal is sent to the PCM.
3. As the PCM increases the amount of fuel injection according to the lean signal, oxygen concentration in the exhaust gas decreases and the condition is back to the situation described in Step 1.

This control process, however, will not take place under any of the following conditions:

^ At engine start and when fuel injection is increased after engine start.
^ When Engine Coolant Temperature (ECT) sensor is low.
^ When highly loaded and fuel injection is increased.
^ At fuel cutoff.
^ When HO2S 1 is cold ("Open Loop" operation).
^ When engine is running at high speed (higher than about 4000 RPM).