Misfire Monitor Operation

There are two different misfire monitoring systems used: a low data rate (LDR) and a high data rate (HDR). 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 on these engines meets the full-range of misfire phase-in requirements specified in the OBD regulations. The PCM software allows for detection of any misfires that occur six engine revolutions after initially cranking the engine. This meets the OBD requirement to identify misfires within two engine revolutions after exceeding the warm drive, idle RPM.