Misfire Detection

The mechanical misfire detection on the M44 engine, required for OBD II, is similar in operation to the M73 system. However now the engine speed and reference sensor is mounted on the rear side of the block and the trigger wheel is mounted to the crankshaft. This allows the DME to precisely monitor the individual cylinders for any misfire condition The rubber mounted crankshaft damper is not sensitive enough to allow precise signalling.

The DME monitors the speed (angular velocity) of the crankshaft from ignition pulse to ignition pulse. The speed of the crankshaft effectively increases each time a cylinder tires on the power stroke. If a cylinder misfires, this change in velocity is no longer present and the respective fuel injector is switched "OFF". A fault is logged in the memory of the DME and depending on how many times or how long the misfire occurs, the "Check Engine" lamp will illuminate.