Engine speed fluctuations have been used to detect and identify misfiring cylinders in multi-cylinder internal combustion engines for many years. The bulk of previous research in this area has concentrated upon steady-state engine operation while sampling engine speed many times during each crankshaft revolution. This paper examines the use of engine speed fluctuations for diagnostic purposes during free acceleration and deceleration of the engine and the possible advantages of transient testing over steady-state testing Previous researchers employed crankshaft encoders or similar devices, which are not available on production engines, to sense angular position. This paper examines the use of the spark initiation signal, from which most present shop diagnostic equipment determines engine speed. Methods for testing overall engine torque and cylinder-to-cylinder torque balance using the spark initiation signal are investigated.