To handle the difficulty of judging fault cylinders in diesel engine misfire failure under high speed and low load conditions

a method that locates fault cylinders by detecting the start of crankshaft torsional vibration in rotation speed signal was proposed. With analyzing the rotation speed signal pattern in single-cylinder misfire

this method first determined the natural frequency of crankshaft torsional vibration

through which a sine vibration detecting signal was built. Then

the inner product of the detecting signal and speed signal during the working stroke of each cylinder was calculated and used as the indicator of fault cylinder. The proposed method was proven by a misfire experiment on a six-cylinder diesel engine to be able to diagnose with high accuracy single-cylinder and double-cylinder misfire faults under high speed and low load conditions

extending the diagnosing scope that the conventional methods cannot cover.