For 1990-2009 cars

Cause | Correction
--- | ---
Abnormalities, such as 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.
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 flex plate or crankshaft balancer A misfire code may be present without an actual misfire condition. | Repair or replace the flex plate and/or balancer, as required. Refer to Automatic Transmission Flex Plate Removal and Automatic Transmission Flex Plate Installation, or Crankshaft Balancer Removal and Crankshaft Balancer Installation.
Worn 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. Refer to Cylinder Leakage Test.
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.