Multiple Cylinder Mis-Fire (OBD II)

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. When a large enough RPM difference occurs between cylinders, a misfire count of 1 is recorded. 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
- Injectors
- Fuel pump or filter
- Restricted exhaust
- Injector harness connectors
- Intake rest action
- Ignition coil circuit
- PCM
- Spark plug
- Evap system
- Mechanical engine problem
- EGR system
- Contaminated fuel
- Air gap at high RPM'S
- Water in fuel
- Mechanical
- PCM power grounds
- Damaged trigger wheel