Abstract: The ignition spark events of the cylinders of an internal combustion engine are timed to provide peak cylinder combustion pressure at a predetermined engine crankshaft angle relative to piston top dead center. The engine crankshaft angle at which the peak cylinder combustion pressure of a selected monitored engine cylinder occurs during each power stroke thereof is detected and indicated by a logic signal. An electrical peak pressure error signal indication of the engine crankshaft angle difference between the crankshaft angle at which peak cylinder combustion pressure actually occurs and the predetermined desired engine crankshaft angle is electronically generated during the period of time required for the engine crankshaft to rotate through a constant predetermined engine crankshaft angle at all engine speeds.