Base Engine Misfire with Abnormal Internal Lower Engine Noises
| 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, noises similar to a faulty lower engine, and also lead to a misfire condition. 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 A misfire code may be present without an actual misfire condition. | Inspect the components. 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. |
| Worn piston rings Oil consumption may or may not cause the engine to misfire. | Inspect the spark plugs for oil deposits. Inspect the cylinders for a loss of compression. Refer to Engine Compression Test . Perform cylinder leak down and compression testing to determine the cause. Repair or replace, as required. |
| Worn crankshaft thrust bearings Severely worn thrust surfaces on the crankshaft and/or thrust bearing may permit fore and aft movement of the crankshaft, and create a DTC without an actual misfire condition. | Replace the crankshaft and bearings, as required. |
