Abstract: The present invention gathers and processes engine speed and position information gathered during cranking, without fuel injection or combustion, in order to derive a set of parameters that are shown to correlate very well with the presence of cylinder compression leakage. Using engine speed and position information from, for example, camshaft gear targets, crankshaft tonewheels, or the flywheel itself, etc., a parameter designated as "metric distance" between adjacent firing cylinder speed fluctuation pulses is determined. For engines with well-balanced cylinder compression, the values of the metric distances measured between all cylinders should be close to each other within a certain threshold. If a cylinder exhibits leakage, the metric distance of the cylinder from its adjacent firing cylinders will significantly exceed the threshold, thereby detecting a leaking cylinder. The method of the present invention also provides a relative estimation of the percentage compression loss from the leaking cylinder.