Measurement Principle
The method of engine misfire detection is based on monitoring the crankshaft acceleration.
The engine roughness is derived from the differences from the segment periods (90°F crank angle) duration, which are corrected and compared to load and engine-speed dependent thresholds. Different statistical methods are used to distinguish between normal changes of the segment duration and changes due to misfire.
The segment periods are measured through an angular range of 90°F crank angle. The segment starts 54°F before TDC. The beginning and end of the segments are located at the same angle. The duration of the crankshaft segments is measured continuously.