For 1990-2009 cars

Cause | Correction
--- | ---
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 and lead to a misfire DTC. 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 may lead to a misfire DTC. A misfire code may be present without an actual misfire condition. | Inspect the components and repair or replace as required.
Loose or improperly installed crankshaft balancer A misfire code may be present without an actual misfire condition. | Repair or replace the flywheel and/or balancer as required.
Loose torque converter bolts A misfire code may be present without an actual misfire condition. | Inspect the torque converter bolts and flywheel and repair or replace as required.
Loose or improperly installed engine flywheel A misfire code may be present without an actual misfire condition. | Repair or replace the flywheel and/or balancer as required.
Restricted exhaust system A severe restriction in the exhaust flow can cause significant loss of engine performance and may set a DTC. Possible causes of restrictions include collapsed or dented pipes or plugged mufflers and/or catalytic converters. | Repair or replace as required.
Air in fuel system | Inspect fuel filter, fuel system for leaks and/or restrictions and repair or replace as required.
Bent and/or worn valve pushrod | Inspect valve pushrod and valve rocker arm and repair or replace as required.
Worn or loose rocker arms The rocker arm bearing end caps and/or needle bearings should be intact and in the proper position. | Replace the valve rocker arms as required.
Improperly installed or damaged vacuum hoses | Repair or replace as required.
Improper sealing between the intake manifold and cylinder heads or throttle body. | Replace the intake manifold, gaskets, cylinder heads, and/or throttle body as required.
Sticking valve Carbon buildup on the valve stem can cause the valve not to close properly. | Repair or replace as required.
Excessively worn or mis-aligned timing belt | Replace the timing belt and sprockets as required.
Damaged or misaligned timing gears | Inspect timing gears and replace as required.
Worn or faulty camshaft lobes | Replace the camshaft and valve lash adjusters.
Excessive oil pressure A lubrication system with excessive oil pressure may lead to excessive valve lifter pump up and loss of compression. |

• | Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing.

• | Repair or replace the oil pump as required.

Faulty cylinder head gasket and/or cracking or other damage to the cylinder head and engine block cooling system passages Coolant consumption may or may not cause the engine to overheat. |

• | Inspect the cylinder head, engine block, and/or head gasket.

• | Repair or replace as required.

Worn piston rings Oil consumption may or may not cause the engine to misfire. |

• | Inspect the cylinders for a loss of compression. Refer to Engine Compression Test.

• | Perform cylinder leak down and compression testing to identify the cause.

• | Repair or replace as required.

Overfilled Crankcase |

• | Check engine oil level with vehicle on a level surface.

• | Correct any overfilled condition.

• | Inspect for fuel leaks into the crankcase. Refer to Fuel in Engine Oil.

• | Repair any fuel leaks.