Misfire Monitor Operation

A low data rate (LDR) and high data rate (HDR) are the 2 different types of misfire monitoring systems used. The LDR system is capable of meeting the federal test procedure monitoring requirements on most engines and is capable of meeting the full range of misfire monitoring requirements on 4-cylinder engines. The HDR system is capable of meeting the full range of misfire monitoring requirements on 6-cylinder and 8-cylinder engines. The HDR system on these engines meets the full range of misfire phase-in requirements specified in the on board diagnostic (OBD) regulations. The PCM software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the OBD requirement to identify misfires within 2 engine revolutions after exceeding the warm drive, idle RPM.