Catalyst Damaging Misfire

DTC P0303
Catalyst damaging misfire cyl 3 Drive cycle C:Signal out of range - above maximum.

Possible causes by suggested order of priority:
- HT problem cylinder 3.
- Ignition coil problem cylinders 2 and 3.
- Ignition coil problem cylinders 2,3,5,8.
- Faulty fuel injector cylinder 3.
- Cylinder 3 combustion efficiency problem.

HT problem cylinder 3.
CHECK THE FOLLOWING:
- Misfire counts high for cylinder 3.
- Misfire counts close to normal for cylinder 2.
POSSIBLE FAULTS
- Spark plug problem cylinder 3.
- HT lead problem cylinder 3
DIAGNOSTIC HINTS
- Problems with the ignition coil or open circuit HT would probably give elevated misfire counts on cylinder 2 also.

Ignition coil problem cylinders 2 and 3.
CHECK THE FOLLOWING:
- Misfire counts high for cylinder 3.
- Misfire counts also raised for cylinder 2.
POSSIBLE FAULTS
- Spark plug problem cylinder 2 or 3 - No spark.
- Open circuit HT lead problem cylinder 2 or 3
- Ignition coil problem - coil pack 1 (cylinders 2,3,5,8)
DIAGNOSTIC HINTS
- Problems with the ignition coil or open circuit HT also show elevated misfire counts on cylinder 2 due to the wasted spark ignition system.

Ignition coil problem cylinders 2,3,5,8.
CHECK THE FOLLOWING:
- Misfire counts high for cylinder 3.
- Misfire counts also raised for cylinders 2,5,8.
POSSIBLE FAULTS
- Problem with 12v supply to coil pack 1 (cylinders 2,3,5,8).
- Coil pack 1 faulty
DIAGNOSTIC HINTS
- Problems with the ignition coil pack also show elevated misfire counts on cylinders 2,5,8 as sparks for these cylinders are also driven from this coil pack.

Faulty fuel injector cylinder 3.
CHECK THE FOLLOWING:
- Misfire counts high for cylinder 3.
- Misfire counts close to normal for cylinder 2.
POSSIBLE FAULTS
- Fuel injector fault cylinder 3.
DIAGNOSTIC HINTS
- Problems with lack of fuel on cylinder 3 can cause a misfire fault to be flagged.
- Fuelling adaptions on bank A may also be affected.

Cylinder 3 combustion efficiency problem.
CHECK THE FOLLOWING:
- Cylinder 3 compression.
- Cylinder 3 leakage.
- Cylinder 3 valve timing (CAM).
POSSIBLE FAULTS
- Valve, Piston or CAM problems causing low efficiency on cylinder 3.
DIAGNOSTIC HINTS
- With low efficiency problems, disconnecting injector 3 will cause little or no effect on idle air flow.