Specific/Random Cylinder Misfire Detection

The ECM receives signals from the crankshaft position sensor to determine the position of the engine at various degrees of rotation. The ECM can then base misfire diagnostics on the principle that crankshaft velocity will increase as each cylinder contributes its power input. If a cylinder fires and the ECM does not see an increase in velocity, it will store misfire counts in 200 revolution segments. If 19 catalyst damaging misfires are detected out of 200 cam revolutions, a DTC will set, the MW (SERVICE ENGINE SOON) light will start flashing and the injector will be turned off.

If 15 emission related misfires are detected out of 100 cam revolutions, a DTC will set, and the MIL (SERVICE ENGINE SOON) light will illuminate. The ECM will set any active misfire counts in memory to zero when the key is turned Off and will test for a misfire under certain conditions. If the MIL light is illuminated it will require three "passes" under the same criteria the misfire was set at or 80 passed "trips" if the criteria was not met.

IMPORTANT: Misfire Logic will not be performed if any of the following conditions exist:
^ TP sensor faults detected.
^ CKP sensor faults detected.
^ IAT sensor faults detected.
^ MAF sensor faults detected.
^ ECT sensor faults detected.

Crankshaft adaptives are automatically learned by the ECM.