Abstract: An engine deficiency indicator includes a detector for detecting a pre-determined amount of angular rotation of an engine. The detector generates a first signal upon the start of one period of rotation of the engine which enables a counter for counting clock pulses. A second signal from the sensor, indicative of the completion of the pre-determined amount of angular rotation of the engine, disables the counter. A processing unit reads and stores the counter data in a memory. The counter data corresponds to the time required for the engine to rotate through a pre-determined amount of angular rotation. At the completion of a pre-determined number of engine rotational cycles, the processing unit analyzes the stored time sequence signals using a discrete Fourier transform analysis and/or an autocorrelation analysis to generate a manifestation of deficient engine operation. A display connected to the processing unit provides a visual or audible indication of efficient or deficient engine operation.