Base Engine Misfire with Abnormal Internal Lower Engine Noises

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

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 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.