Abstract: To diagnose misfires of an individual cylinder accurately and easily, a new method using phase angles of harmonic torsional vibrations of a crankshaft was developed according to the principle of internal combustion engine dynamics. The misfire cylinder can be detected with the new method without a requirement for any experience. The method was confirmed through simulation and experiments on a 6135ZG type diesel engine. The results show that the misfire cylinder can be determined by phase angle of 0.5 order torsional vibration displacement accurately