Base Engine Misfire with Abnormal Internal Lower Engine Noises

Engine Mechanical - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5132363 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 as required.
	Loose or improperly installed automatic transmission flex plate or crankshaft balancer A misfire code may be present without an actual misfire condition.	Repair or replace the automatic transmission flex plate and/or balancer as required.
	Loose torque converter bolts A misfire code may be present without an actual misfire condition.	Inspect the torque converter bolts and automatic transmission flex plate. Repair or replace as required.
	Worn piston rings Oil consumption may or may not cause the engine to misfire.	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.
	Overfilled crankcase	1. Check engine oil level with vehicle on a level surface. 2. Correct any overfilled condition.
	© 2023 General Mo	tors. All rights reserved.

Cause	Correction
	3. Inspect for fuel leaks into the crankcase. 4. Repair any fuel leaks.