Note. DTC P0300 is set when the ECM recognizes a general misfire in the engine. If the ECM determines the cylinder causing the misfire it will set a specific DTC P0301-P0308, to indicate the number of the cylinder causing the misfire. If a DTC P0301-P0308 is retrieved, use this procedure to diagnose the misfire condition in the indicated cylinder.
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.