Abnormalities, severe cracking, bumps or missing areas in the accessory drive belt

Abnormalities in the accessory drive system and/or components may cause engine RPM variations, noises similar to a faulty lower engine and also lead to a misfire condition. A misfire code may be present without an actual misfire condition.

Replace the drive belt. Refer to Drive Belt Replacement .

Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout

A misfire code may be present without an actual misfire condition.

Inspect the components and repair or replace, as required.

Loose or improperly installed engine flywheel or crankshaft balancer

A misfire code may be present without an actual misfire condition.

Repair or replace the engine flywheel and/or crankshaft balancer, as required.

Refer to Engine Flywheel Replacement or Crankshaft Balancer Replacement .

Worn or broken piston rings

Oil consumption may or may not cause the engine to misfire.

1. Inspect the spark plugs for oil deposits. Refer to Spark Plug Inspection .
2. Inspect the cylinders for a loss of compression. Refer to Engine Compression Test .
3. Perform cylinder leak down and compression testing to determine the cause.
4. Repair or replace, as required.

Worn crankshaft thrust bearings

Severely worn thrust surfaces on the crankshaft and/or thrust bearing may permit fore and aft movement of the crankshaft and create a DTC without an actual misfire condition.

Replace the crankshaft and bearings, as required.