Engine oil level overfull, causing aeration

Drain excess oil and adjust oil level to proper specification.

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. Refer to Drive Belt Tensioner Replacement .

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 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.

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.

Worn or bent pushrods

Replace the pushrods.

Stuck valves--Carbon buildup on the valve stem can cause the valve not to close properly.

Repair or replace as required.

Excessively worn or out of time 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--Refer to Diagnostic Starting Point - Engine Cooling .

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. 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. 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.
4. Repair or replace as required.

Faulty Cylinder Deactivation (Active Fuel Management) Lifter

An Active Fuel Management (AFM) lifter with a locking pin stuck in the disengaged mode can cause a rough running condition.

Check for a faulty AFM lifter. Refer to Cylinder Deactivation (Active Fuel Management) System Compression Test.