Vibration signals from diesel engines were analyzed for the purpose of isolating signals relating to injection or combustion which could be used to time the engines. Nonintrusive sensors, magnetically attached to the engine, were used to obtain these vibration signals. Components believed to be associated with combustion or fuel injection were electronically isolated from the remaining engine noise, and subsequently processed to produce specific timing signals. Digital data acquisition and averaging methods were used, coupled with computerized frequency analysis. The signals were experimentally correlated with the combustion process over a wide range of injection timing. The electronic processing system developed provides a real time digital measure of the timing. Data on the accuracy and correlation of experimental measurements will be presented.