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.