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Cause
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Correction
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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 dtc code may be present without an actual misfire condition.
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Replace the drive belt. Refer to
Drive Belt Replacement
.
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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.
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Inspect the components, repair or replace as required.
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Loose or improperly installed engine flywheel or crankshaft balancer
A misfire code may be present without an actual misfire condition.
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Repair or replace the flywheel and/or balancer as required. Refer to
Engine Flywheel Replacement
or
Crankshaft Balancer Replacement
.
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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.
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Repair or replace as required.
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Improperly installed or damaged vacuum hoses
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Repair or replace as required.
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Improper sealing between the intake manifold and cylinder heads, intake manifold and plenum duct, plenum duct and water crossover, water crossover and throttle body and/or pressure relief valve and intake manifold.
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Replace the intake manifold, plenum duct, gaskets, cylinder heads, throttle body and/or pressure relief valve as required.
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Improperly installed or damaged MAP sensor and/or seal
The sealing grommet of the MAP sensor should not be torn or damaged.
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Repair or replace the MAP sensor as required.
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Improperly installed or damaged EVAP purge solenoid and/or O-ring seal
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Repair or replace the EVAP purge solenoid as required.
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Worn or loose followers, valve rocker arms
The follower, valve rocker arm, roller bearing should be intact and in the proper position
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Replace the followers, valve rocker arms, as required.
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Stuck valves
Carbon buildup on the valve stem can cause the valve not to close properly.
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Repair or replace as required.
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Excessively worn or mis-aligned timing chain or chains
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Replace the timing chain or chains and sprockets as required.
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Worn camshaft lobes
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Replace the camshaft or camshafts and SHLAs, valve lifters.
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Excessive oil pressure
A lubrication system with excessive oil pressure may lead to excessive valve lifter pump-up and loss of compression.
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•
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Repair or replace the oil pump as required.
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Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages. Refer to
Diagnostic Starting Point - Vehicle
.
Coolant consumption may or may not cause the engine to overheat.
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Inspect the cylinder heads, engine block, and/or head gaskets.
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Repair or replace as required.
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Worn piston rings
Oil consumption may or may not cause the engine to misfire.
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Perform cylinder leak down and compression testing to identify the cause.
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Repair or replace as required.
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A damaged crankshaft reluctor wheel
A damaged crankshaft reluctor wheel can result in different symptoms depending on the severity and location of the damage.
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•
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Systems with SEVERE reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then re-sync the crankshaft position.
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Systems with SLIGHT reluctor ring damage may exhibit no loss of crankshaft position and no misfire may occur. However, a P0300 DTC may be set.
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Replace the crankshaft as required.
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