Combustion state diagnosing system and combustion state diagnosing method for diagnosing engine and recording medium

摘要

It is an object of the present invention to provide a low-cost combustion state diagnosing system and a combustion state diagnosing method capable of accurately detecting misfires which occur at a low frequency while a multiple-cylinder engine is operating at a high engine speed under a low load. The object can be achieved, when diagnosing combustion state, by extracting specific rotation period component of a period synchronous with rotation from a combustion state parameter for at least two rotations, and judging combustion state on the basis of the extracted specific rotation period component. The combustion state parameter may be the engine speed or the output torque of a multiple-cylinder engine which varies according to the combustion state of the engine.