Patent US 5,440,922

An apparatus for detecting a misfire in an internal combustion engine includes a rotational signal outputting unit for outputting a rotational signal corresponding to a rotational position of the engine, an average rotational angular speed computing unit for computing an average rotational angular speed of the engine based on the rotational signal, a deviation computing unit for computing a deviation of a computation result of the average rotational angular speed computing unit at every predetermined rotational position, and a misfire determining unit for determining occurrence of a misfire based on a pattern of the relative magnitude of three consecutive values of the deviations obtained at every predetermined rotational position. Further, the misfire determining unit may use a difference of the deviation, which is computed separately, in place of the deviation itself.