The objective of this paper is to describe the potential of an alternative method for engine misfire detection, whose main characteristic is the analysis of exhaust pressure pulsation. Its theoretical basis is that, when the combustion is regular, the exhaust valve openings of the various cylinders generate strong pressure pulses, that have similar amplitudes; when there is misfire in a cylinder, the relevant pressure pulse is substantially modified. So, in principle, the pressure pulsation profiles in the exhaust system, together with a phase reference obtained by a cam sensor, contain all “information” needed for misfire detection.
The paper will introduce a powerful tool to extract this “information”, based on an algorithm whose main component is a Fourier Transform of the pressure signals acquired during the engine cycle. In particular, it will be shown how a suitable management of the amplitudes and phases of the harmonics of these signals can lead to a reliable misfire index, also allowing the identification of the cylinder that is undergoing misfire, in single misfire events.