Misfire Detection

Legislation requires that the engine control module (ECM) must be able to detect the presence of an engine misfire. It must be able to detect misfires at two 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 engine control module (ECM) monitors the number of misfire occurrences within two engine revolution ranges. If the engine control module (ECM) determines a misfire failure within either of these two ranges, over two consecutive journeys, it will record a fault code and details of the engine speed, engine load and engine coolant temperature. In addition, if the second level of misfire occurs, on any trip, the engine control module (ECM) flashes the malfunction indicator lamp (MIL) while the fault is occurring.

The signal from the crankshaft position (CKP) sensor indicates how fast the poles on the drive plate are passing the sensor tip. A sine wave is generated each time a pole passes the sensor tip. The engine control module (ECM) can detect variations in drive plate speed by monitoring the sine wave signal supplied by the crankshaft position sensor. By assessing this signal, the engine control module (ECM) can detect the presence of an engine misfire. The engine control module (ECM) will evaluate the signal against a number of factors and will decide whether to record the occurrence or ignore it. The engine control module (ECM) can assign a misfire judgement to an individual cylinder, which can be viewed on Land Rover approved diagnostic equipment.