Detecting combustion misfiring in motor vehicle four-stroke IC engine

The method detects faults in the combustion of a z-cylinder four stroke combustion engine. The engine has a generator wheel coupled to a crank shaft to rotate in phase synchrony with the crank shaft. The wheel typically has half as many segments as cylinders which are scanned by a sensor device. The latter supplies segment time signals which represent the non-uniformity of the rotation movement of the crank shaft for each cylinder. Run unrest values for each cylinder are formed on the basis of the segment times and a fault is then analysed when the run values exceed a threshold value. The component of the run values with the crank shaft frequency are filtered out before the threshold value comparison. Preferably the signal components at the crank shaft frequency are eliminated by band pass filtering of the useful signal. Alternatively, these components may be eliminated by comb filtering of the interference component.