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 and lead to a misfire diagnostic trouble code (DTC). A misfire code may be present without an actual misfire condition.

Replace the drive belt. Refer to Drive Belt Replacement - Accessory .

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

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

1. Inspect the components.
2. Repair or replace the components, 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 flywheel and/or balancer, as required. Refer to Engine Flywheel Replacement or Crankshaft Balancer Replacement .

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.

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

The sealing grommet of the MAP sensor should not be torn or damaged.

Repair or replace the MAP sensor, as required.

Worn or loose rocker arms

Repair or replace the valve rocker arms, as required.

Worn or bent push rods

Replace the push rods.

Sticking valves

Carbon buildup on the valve stem and/or seat can cause the valve to not close properly.

Repair or replace, as required.

Excessively worn or mis-aligned timing chain

Repair or replace the timing chain, camshaft retainer, 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. Refer to Spark Plug Inspection .
2. Perform a pressure test to the cooling system. Refer to Loss of Coolant .
3. Inspect the cylinder heads, engine block, and/or head gaskets. Refer to Coolant in Combustion Chamber .
4. 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. 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 identify the cause. Refer to Cylinder Leakage Test .
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.

Replace the sensor and/or crankshaft reluctor wheel, as required.