Severe Engine Miss

[f5fstop]

Might be the problem, but no guarantees...
All I could find on the subject....

Subject: P0300 Cylinder 7 Misfire Due To Fuel System Contamination - keywords CEL contaminated DTC engine gas L59 L76 L92 LC9 LMG LR4 LM7 LY2 LY5 LY6 LQ4 LQ9 miss P0302 P0307 P0308 SES tank water #PIP3055A - (09/26/2006)
Models: 2001-2007 Cadillac Escalade
1999-2007 Chevrolet Avalanche, Express, Silverado, Suburban, and Tahoe
1999-2007 GMC Savana, Sierra, Yukon
2003-2007 Hummer H2
--------------------------------------------------------------------------------
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A dealer may encounter a customer concern of a SES light on and a engine misfire. The misfires will accumulate mostly on the number 7 cylinder. A possible cause could be fuel contamination. If present, the contaminated fuel will collect around the #7 fuel injector due to the fuel rail configuration in these vehicles. Fuel contamination can also cause random misfires to occur on other cylinders.

Recommendation/Instructions:
If the published misfire diagnostic does not isolate the concern, the following suggestions may help if the misfire is related to fuel contamination:

Complete the SI repair procedure for Fuel Rail Assembly Replacement. When the fuel feed pipes are removed, cap off the fuel rail inlet so the contents can be inspected for contamination. Drain the fuel rail into a clean approved container, and inspect the fuel.
If contamination is found, follow the current SI Fuel System Cleaning procedure.
Once the fuel system is cleaned, refill the fuel system with new gasoline.
Advise the customer that they should only use gasoline from a high quality, high volume filling station.
If this is a 99 - 00 Chevrolet Silverado or GMC Sierra, also review 00-06-04-024. This bulletin relates to an updated EVAP vent valve to prevent water from being drawn in through the EVAP Vent Valve, which may lead to repeat fuel contamination.

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.