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This paper describes the method to detect S. I. engine misfire for the OBD II requirement. In most methods related to the misfire detection, the fluctuation of crankshaft speed is used as an input parameter[1, 2, 3, 4 and 5]. If the misfire detection is performed by the pattern of crankshaft speed without considering the engine dynamics, it is difficult to determine the misfire at high speed and low load condition. So this paper proposed the single degree of freedom energy model of engine dynamics for the misfire detection. Through this model the integral of torque by cylinder pressures are estimated using the variation of crankshaft speed and it is possible to detect the misfire by this integral value.

This paper describes to measure the cylinder pressure in a SI engine using the variation of crankshaft speed. Assuming engine dynamics as a single degree of freedom the energy equation is derived. Through some assumptions each cylinder pressure can be estimated form the pressure torque. Through this study cylinder pressures by this method show good accord with measured value in low to medium speed ranges. For more accurate analysis the crank angle based modeling of friction and vibration is required.