Detection of misfiring

To detect misfiring, the rough running of the engine is evaluated. To this aim, the flywheel (1 crankshaft revolution) is divided into three segments.

The RPM/crankshaft position sensor measures the period of time which passes until the segment has moved past the RPM/crankshaft position sensor.

If combustion misfiring occurs, the drive torque is reduced briefly. This leads to an interruption in the RPM and therefore to a longer segment time, or to negative angular acceleration. The rough running of the engine is proportional to the change in angular acceleration. At constant RPM or constant acceleration, rough running equals zero.

Marked changes in RPM also occur during dynamic engine operation, and these must be distinguished from combustion misfiring. It is possible to distinguish between them, as the change in RPM extends over more revolutions than in the case of combustion misfiring.