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Certain harmonics of angular crankshaft velocity are indicative of engine imbalance induced by cylinder misfire. Application of the Digital Fourier Transformation (DFT) facilitates the production-feasible calculation of a singular index in the frequency domain indicative either of smooth engine operation or misfire. The phase of that particular index with proper interpretation directly points to a misfiring cylinder. The identification of a misfiring pair, either opposing or a non-opposing in the cylinder bank, requires a bit more sophisticated approach since the phase response of the characteristic index in the frequency domain becomes more complex. The method demonstrated here was successfully applied in real time in four-, six-, and eight-cylinder engines, both SI and Diesel, for the On-Board Diagnostic application with reliability exceeding relevant regulatory requirements.