Advanced engine maintenance programs incorporate various methods for monitoring the engine parts so as to be able to foresee malfunctions and interruptions of normal operation. The present study is concerned with the development of a vibration signature analysis method for early fault detection and diagnosis in internal combustion engines. The successful implementation of this simple and straightforward method in many maintenance programs motivates the application of this method to the class of SI engines. An acceleration transducer is mounted on the engine and the vibration signals are recorded during the engine operation. The measurements are then transformed to the frequency domain where the frequencies and the amplitudes of the harmonic components of the vibrations waveform are analyzed and compared to the corresponding vibration signature under normal operation conditions. Preliminary results that were obtained in the course of the present study demonstrate that damaged engine mountings, misfiring, fouled spark plugs, worn spark plugs, improper spark timing, and off-timing valves, can be detected with this method.