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Another Missfire Thread

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Ok I have done a bunch of reading and so far no luck. I have an 04 Silverado 3500 with the 6.0 I recently bought with a random missfire P0300. That’s the only code that shows up. The misfires are on both banks and primarily occur when I quickly depress the accelerator. I’ve got 60 psi fuel pressure and it holds steady at 55 when I shut the truck off. I did an injector flow balance and they look equal. Did the crank relearn procedure. Pulled one of the spark plugs and it looks lean. The 02 sensor readings look strange to me. The upstream ones bounce between mid 800’s and 200’s. Bank 1 down stream holds steady at idle around 150, Bank 2 is bellow 100. When I give it gas bank two mirrors the upstream one but bank one stays fairly steady in the mid 100’s. Any ideas?

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13 hours ago, CamGTP said:

What do your fuel trims look like? The long term trims.

No more than 8%.  As of right now I seem to have done something that fixed it.  It still shows an occasional missfire on the scanner but it's not counting up so isn't triggering the check engine light.  Going to throw a set of fresh plugs in it today.  There is also an exhaust leak at the rear of the manifold from a missing bolt I need to tackle.  Debating on if I should throw a set of headers on if I have to pull the manifold anyway. 

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