Multiple Cylinder Misfire

Name of Code:
Multiple Cylinder Misfire

When Monitored:
With the engine running, after successfully performing a crank sensor learn.

Set Condition:
When more than a 2% misfire rate is measured during two trips, or with a 10% to 30% misfire rate during one trip.

Theory of Operation:
Misfire is detected by the crankshaft speed fluctuation (CSF) method. This method compares the engine speed difference between the cylinders in firing order. The speed is detected by the crankshaft position sensor. An RPM value is set for each cylinder for comparison. When an RPM difference of more than 10 RPM occurs between cylinders, a misfire count of 1 is recorded. The RPM can vary between 1 and 10 because of different engine loads. Two types of misfire are detected: a two-trip misfire, which is about 2% and results in an emissions increase, or a one-trip misfire, which is about 10-30% and will cause damage to the catalytic converter.

Possible Causes:
- Secondary ignition wires
- PCM power grounds
- Fuel pump or filter injectors
- Injector harness connectors
- Restricted exhaust
- Ignition coil circuit
- Intake restriction
- Spark plug
- PCM
- Mechanical engine problem
- EVAP system
- Contaminated fuel
- EGR System