Abstract: A new approach using the average effective pressure of each cylinder to diagnose the power distribution of a multi-cylinder engine is developed, in which the average effective pressure of each cylinder is calculated from measured crankshaft torsional vibrations. Specifically, the transfer function between the average effective pressure among cylinders and the measured crankshaft torsional vibrations is obtained by the sub-space method of dynamic condensation, and then the average effective pressures are obtained by solving contradiction equations with the least square method. The suggested diagnosis method is confirmed through experiments on 6135 type diesel engine.