Misfire Adaptive Numerator at Limit

Name of Code:
Mis-Fire Adaptive Numerator at Limit

When Monitored:
Under closed throttle deceleration; A/C off, engine coolant temperature above 75 degrees; longer than 50 seconds after engine start. The speed at which the deceleration occurs must be sufficient for the given gear range; e.g. above 36 mph in first gear or above 65 mph in high gear.

Set Condition:
When one of the CKP sensor target windows (40 degrees) has more than 2.86% variance from the reference window.

Theory of Operation:
Because of the need for increased engine RPM resolution to detect a misfire, machining variation has to be learned. The crankshaft has two 40 degree windows that are 180 degrees apart. The window for cylinders #1 and #4 is the reference window. This window position is checked against the window for cylinders #2 and #3. If the reference window detects a variance the PCM will learn this variance and make the appropriate RPM adjustment. If the variance exceeds 2.86% the trouble code will set.

Possible Causes:
- Crankshaft position sensor improperly installed
- Crankshaft position sensor failure
- Crankshaft position sensor crankshaft target variation
- Severely worn crankshaft bearings
- Wiring connector
- PCM failure
- Low compression in one or more cylinders