Abstract: A stroboscopic timing system for diesel engines of the type having apertures in each cylinder for normally accepting glow plugs. A signal that varies in accordance with pressure changes within the cylinder is generated by a piezoelectric transducer mateable with a glow plug aperture, and the transducer signal is processed by filtering and other discriminating circuitry to provide a timing pulse that occurs upon the initiation of combustion within the cylinder. A conditioning circuit shapes this pulse into suitable form for triggering a high intensity stroboscopic light for illuminating timing marks on the engine drivetrain.