Misfire Detection Monitor: Notes

The misfire detection monitor is an on board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire occurred. Misfire is detected using the crankshaft position (CKP) and camshaft position (CMP) sensors. To determine if a misfire has occurred the powertrain control module (PCM) monitors deceleration of the crankshaft and compares the information received to engine speed and engine load. If a misfire event is determined, the PCM uses the CKP and the CMP sensor signal information to determine which cylinder misfired.

The misfire event is defined as poor compression, fuel delivery, or mechanical engine failure. The misfire detection monitor is enabled only when certain base engine conditions are first satisfied. Input from the engine oil temperature (EOT), CKP, mass fuel desired (MFDES), exhaust pressure (EP), intake air temperature (IAT), fuel level input (FLI) and injector control pressure (ICP) sensors is required to enable the monitor.

1. The CKP signal generated is the main input used in determining cylinder misfire.
2. The input signal generated by the CKP sensor is derived by sensing the passage of the teeth from the crankshaft position wheel, which is mounted on the crankshaft.
3. The input signal to the PCM is used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value, and other criteria is met, the suspect cylinder is determined to have misfired.