During the internal combustion engine operation some faults in the combustion process can occur, affecting the overall engine performance. Nowadays, aimed at detecting such faults, different techniques are adopted, which are mainly based on the identification of key parameters characterizing both regular and fault engine running. The engine vibration and the engine instantaneous angular velocity are generally used as monitoring signal. In this paper an experimental methodology based on the processing of the exhaust pressure signal is considered. The results obtained in a test cell on a SI four cylinder engine are presented.