Base Engine Misfire with Abnormal Internal Lower Engine Noises

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

Condition	Action
Abnormalities (severe cracking, bumps or missing areas) in the accessory drive belt.	Abnormalities in the accessory drive belt 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. Inspect the accessory drive components. Repair or replace all damaged components.
Worn, damaged, or misaligned accessory drive components or excessive pulley runout	A misfire code may be present without an actual misfire condition. Inspect the accessory drive components. Repair or replace all damaged components.
Loose and/or damaged crankshaft balancer	A misfire code may be present without an actual misfire condition. Inspect crankshaft balancer and balancer bolt. Repair or replace all damaged components.
Loose torque converter bolts	A misfire code may be present without an actual misfire condition. Inspect torque converter bolts and flywheel. Repair or replace all damaged components.
Loose and/or damaged flywheel	A misfire code may be present without an actual misfire condition. Inspect flywheel and flywheel attaching bolts. Repair or replace all damaged components.
Excessive piston-to-cylinder bore clearance	Perform cylinder leak down and compression tests Inspect the piston, piston rings and cylinder bore. Repair or replace all damaged components.
Excessive crankshaft thrust bearing clearance	Severely worn thrust surfaces on the crankshaft and/or thrust bearing may permit for and aft movement of the crankshaft and create a misfire code without an actual misfire condition. Inspect the crankshaft end play and crankshaft thrust bearings. Repair or replace all damaged components.
Overfilled crankcase	Check engine oil level with vehicle on a level surface. Correct any overfilled condition. Inspect for fuel leaks into the crankcase. Repair any fuel leaks.