Abstract: A method of determining a goal voltage for a fuel/air sensor of an engine electronic fuel injection system includes the steps of determining a goal fuel/air sensor voltage, superimposing a wave form forcing function to the fuel/air sensor voltage for providing a goal fuel/air sensor voltage having a wave form pattern and controlling the engine to operate according to the goal fuel/air sensor voltage. The wave form forcing function provides the required fuel/air perturbations that are required to retain proper oxygen storage of the catalyst to maintain high three-way conversion efficiency.

Abstract: A methodology of computing a combustion stability value and using the combustion stability value to control engine operation is provided. The combustion stability value is determined by monitoring engine operation. The combustion stability value is compared to an expected combustion stability value. Where the combustion stability value is greater than the expected combustion stability value, combustion of the internal combustion engine is controlled as a function of the combustion stability value. Where the combustion stability value is not greater than the expected combustion stability value, combustion of the internal combustion engine is controlled as a function of an O2 sensor value. In either case, engine control is accomplished by modifying a target fuel injection value.