GM Repair Problems? Ask GM Repair Expert Now.
What you describe sounds like a bad rocker arm (the are called valve keepers sometimes) or a bad lifter. Does it sound like the noise is mostly from the top end of the engine?
Have you performed a compression test yet?
Whenever I see knock that only occurs above 2500 RPM or so it's almost always a worn rocker arm. They aren't terribly hard to replace. You have to remove the valve cover and install the new rocker on the failed cylinder. From the look of those codes it's most likely cylinder #1. Do you plan to tackle it yourself?
If it was a bad camshaft it would probably misfire on all cylinders and it would just be wimpy rather than backfire.
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