Subject: | GEN III or Gen IV V-8 Engine Misfire |
Models: | 1999-2006 Chevrolet Express, Silverado, Tahoe |
1999-2006 GMC Savana, Sierra, Yukon |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Engine misfire 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.
General Motors Brand Quality and Engineering is interested in any V-8 engine with a cam lobe or lifter concerns. This would include any excessive wear to the lifter roller, or the cam lobe itself.
A complete compression test, an 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 diagnostics are listed below, and 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.
In the event a flat spot or pitting is discovered on the lifter or cam, please contact Brand Quality Manager Jay Dankovich to discuss the repairs, and parts returns.
Contact can either be made by E-mail or phone call.
Jay Dankovich
jay.dankovich@gm.com
586-947-8881
When contacting Jay Dankovich the root cause should have already been found. Engineering is looking only for cam lobe or lifter concerns.
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.