| Subject: | Cylinder 1 Misfire on Deceleration and Cylinder 6 Misfire on Acceleration - Check for Contamination in Fuel Rail |
| Models: | 2005-2006 Buick Rainier |
| 2005-2006 Chevrolet Trail Blazer |
| with 4.2L Engines (VIN S - RPO LL8) |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Fuel contamination may cause a misfire that occurs on cylinder 1 during or shortly after deceleration and on cylinder 6 during or following hard acceleration. Due to the returnless fuel rail system that this engine is equipped with, fuel does not return
to the fuel tank from the fuel rail. As a result, fuel contaminates may become trapped in the fuel rail and eventually pass through the number 1 fuel injector during deceleration and through the number 6 fuel injector on acceleration. Typically, this misfire
will last for 2 - 10 seconds and although any misfire DTC could set, typically DTCs P0300, P0301, and P0306 will set as a result of this.
Recommendation/Instructions:
If this condition is encountered, inspect the inside of the fuel rail and fuel tank for signs of fuel contamination. If fuel contamination is present, refer to the "Fuel System Cleaning" procedure in SI and clean the inside of the fuel tank, fuel lines,
and fuel rail. Once the entire fuel system is cleaned and reassembled, clean the fuel injectors by following the "Fuel Injector Cleaning Procedure" in SI. Also advise the customer that they should only use fuel from a high quality, high volume fuel station.
Repairs made as a result of fuel contamination should not be considered as a warranty repair.
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.
