Abstract: A system and method for accurately detecting misfires in an internal combustion engine which includes an ignition coil 12 with a primary winding 22 and a secondary winding 30, at least one spark plug 62, and an ignition controller 20 responsive to engine operating conditions for generating an ignition signal. Preferably, the ignition coil generates sparking voltage for firing the spark plug in response to the ignition signal. Sparking voltage and firing of an ignition spark are detected (steps 402-410). An average sparking voltage after the firing of the ignition spark and a peak sparking voltage after the firing of the ignition spark are determined (steps 412-420). And, an indication of misfire in response to the average sparking voltage and the peak sparking voltage is provided (steps 422-428).

Abstract: An adaptive method of detecting a misfiring cylinder in a spark-ignited internal combustion engine during substantially all engine operating conditions, including most no-load operation. The method includes the step of normalizing an engine acceleration-independent and engine speed-independent power cycle time differential signal for a particular cylinder of the engine, obtained from consecutive power cycle time periods of an engine cycle, utilizing a calibration parameter stored in the memory for the particular cylinder, to obtain a normalized power cycle time differential signal for the particular cylinder. The method also includes the step of comparing the normalized power cycle time differential signal to a misfire threshold signal stored in the memory to determine if the cylinder is misfiring. Preferably, the misfire threshold signal is based on at least one engine operating parameter.