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.
A loose or improperly installed engine flywheel or crankshaft balancer 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.
Improperly installed or damaged vacuum hoses | Repair or replace, as required.
Improperly installed or leaking charge air cooler tube | 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.
Improperly installed or damaged manifold absolute pressure (MAP) sensor or intake air pressure temp (TMAP) sensor The sealing grommet of the MAP sensor should not be torn or damaged. | Repair or replace the MAP sensor and/or the TMAP sensor, as required.
Damage to the MAP sensor housing | Replace the intake manifold.
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.
Stuck valves 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 chain | Replace the timing chain and sprockets, as required.
Worn camshaft lobes | Replace the camshaft and valve lifters.
Excessive oil pressure A lubrication system with excessive oil pressure may lead to excessive valve lifter pump up and loss of compression. |

1. Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing.
2. Repair or replace the oil pump, as required.

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

1. Inspect for spark plugs saturated by coolant.
2. Inspect the cylinder heads, engine block, and/or head gaskets.
3. Repair or replace, as required.

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

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

A damaged crankshaft reluctor wheel A damaged crankshaft reluctor wheel can result in different symptoms depending on the severity and location of the damage.

• | Systems with electronic communications, DIS or coil per cylinder, and severe reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then re-sync the crankshaft position.

• | Systems with electronic communication, DIS or coil per cylinder, and slight reluctor ring damage may exhibit no loss of crankshaft position and no misfire may occur. However, a DTC P0300 may be set.

• | Systems with mechanical communications, high voltage switch, and severe reluctor ring damage may cause additional pulses and affect fuel and spark delivery to the point of generating a DTC P0300 or P0336.

Replace the sensor and/or crankshaft, as required.