Abstract: An apparatus and corresponding method for detecting misfires of a motor vehicle internal combustion engine. The apparatus includes a speed sensor for generating a signal. Also, the apparatus includes a filter means for filtering noise-related events from said signal corresponding to sensed engine speed to thereby produce a filtered output signal. In addition, a pressure sensor for measuring average manifold absolute pressure over a cylinder firing event to set a misfire threshold change in engine speed value is shown. A comparison means for comparing said filtered output signal with said threshold change in engine speed value to detect an engine misfire condition for said cylinder firing event is also included.

Abstract: A digital filter system is used in an internal combustion engine misfire detection system. The digital filter system includes a signal input for inputting a digital signal generated in response to sensed crankshaft angular velocity. A plurality of digital filters is connected to the signal input, with each of the filters being activated over a predetermined range of engine speeds. Each of the plurality of digital filters, upon being activated, operates as a bandpass filter to filter the digital signal at an engine spatial firing frequency and at a predetermined number of multiples of the engine spatial firing frequency. A signal output is also connected to the plurality of digital filters for outputting the filtered digital signal for engine misfire detection purposes.