Subject: | GEN III or Gen IV V-8 Engine Misfire |
Models: | 1999-2008 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe, Trailblazer |
2006-2008 Chevrolet Impala |
2005-2008 Pontiac Grand Prix |
2007 Silverado Classic Body Style |
1999-2008 GMC Envoy, Savana, Sierra and Yukon |
2007 Sierra Classic Body Style |
This PI was superseded to update models and model years. Please discard PIP4138B.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
An engine misfire that may be caused by lifter roller or camshaft wear on any 4.8 5.3 or 6.0 V-8 engine. The misfire described in this PI may be difficult to diagnose, hard to feel, and can occur on any cylinder.
Complete the current diagnostics for any symptom or trouble code found.
If the vehicle is showing misfires on a single cylinder, and the SI diagnostics are inconclusive, there may be a valve train, or camshaft related concern.
A complete compression test, injector balance test, and a cylinder leakage test must be completed and documented. If these diagnostics are inconclusive, continue with the information found in this PI.
Valve train concerns that are causing difficult to diagnose conditions are listed below. The tests and/or inspections should be completed by the easiest to find to the most difficult.
Thoughts on root causing some of the misfire concerns that may be encountered.
If a camshaft or lifter concern has been verified, complete the current SI procedures to repair the vehicle. Engineering has collected samples of returned parts and is investigating camshaft/lifter concerns. This PI will be updated when new information becomes available.
Note: When diagnosing a misfire on a GEN III or GEN IV engine, and a cylinder head has been removed, replacement of that bank of lifters (if only one head is removed replace only those 8 lifters) is suggested.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.