Base Engine Misfire with Abnormal Internal Lower Engine Noises. GMC Truck Envoy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2003 🢒 Envoy - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Base Engine Misfire with Abnormal Internal Lower Engine Noises

Cause

Correction

Abnormalities, such as 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. Refer to Drive Belt Replacement - Accessory .

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.

Refer to Engine Flywheel Replacement or Crankshaft Balancer Replacement .

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 - 5.3L.

•	Inspect the cylinders for a loss of compression. Refer to Engine Compression Test .

•	Perform cylinder leak down and compression testing to determine the cause. Refer to Cylinder Leakage Test .

•	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.