| Cause | Correction |
|---|---|
| Abnormalities consist of 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 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. | Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing . 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. | Inspect for spark plugs saturated by coolant. Refer to Spark Plug Inspection in Engine Controls. Inspect the cylinder heads, engine block, and/or head gaskets. Repair or replace as required. |
| Worn Piston Rings Oil consumption may or may not cause the engine to misfire. | Inspect the spark plugs for oil deposits. Refer to Spark Plug Inspection in Engine Controls. 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. |
Base Engine Misfire without Internal Engine Noises