5.2.1 Description

Misfire detection is achieved by monitoring the acceleration of the crankshaft, if the speed of the crankshaft reduces and increases after a firing event then a misfire is suspected.

The time for each firing event is measured over 120 crankshaft degrees; this time is corrected for mechanical variation between the different measurement windows. These correction factors are determined during periods of ORFCO.

The corrected segment times from a number of firing events are used to calculate an Engine Roughness (ER) value for each individual firing event, if this ER value is less than the ER threshold for that engine operating point then a misfire has occurred.

Misfire detection is suspended when other factors such as a rough road surface or an extreme change in engine speed influence the rotation of the crankshaft and would result in the false detection of misfire.

Misfire events are processed according to the requirements of the OBD regulation to determine if the MIL should be illuminated and a Diagnostic Trouble Code (DTC) stored.