Misfire Detection

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Legislation requires that the PCM must be able to detect the presence of an engine misfire. It must be able to detect misfires at 2 separate levels.

The first level is an amount of misfire that could lead to the legislated emissions limit being exceeded by a given amount.
The second level is a misfire rate that causes degradation in catalytic converter efficiency.

The PCM monitors the number of misfire occurrences within 2 engine revolution ranges. If the PCM determines a misfire failure, over 2 consecutive journeys, it records a DTC . The PCM also records details of the engine speed, engine load and engine coolant temperature. If the second level of misfire occurs the PCM flashes the MIL in the Instrument Panel Cluster Control Module (IPC) while the fault is occurring.

The signal from the CKP indicates how fast the teeth on the drive plate are passing the sensor tip. A sine wave is generated each time a tooth passes the sensor tip. The PCM detects variations in drive plate speed by monitoring the sine wave signal supplied by the CKP . By assessing this signal, the PCM detects the presence of an engine misfire. The PCM evaluates the signal against a number of factors and decides either to record the occurrence or ignore it. The PCM can assign a misfire judgment to an individual cylinder, which can be viewed on Jaguar Land Rover (JLR) approved diagnostic equipment.