Circuit Description

This test is used to detect misfires in any cylinder. A misfire occurs when there is a complete lack of combustion in the cylinder. A misfire will cause a fluctuation in crankshaft revolution speed. PCM uses the time between 4X reference pulses to determine when these fluctuations occur. At lower speeds, fluctuations in crankshaft speed are measured each reference pulse to detect misfire. At higher engine speeds, fluctuations in crankshaft speed are monitored over 2 engine revolutions and fluctuations in crankshaft speed at each half revolution are compared to compute a balance number. The 4X reference pulses originate in the ignition control module and vary with RPM.