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Intermittent P0308, tested a bunch of it bad rings, fuel pump or?

585 Views 0 Replies 1 Participant Last post by  elwood_
I have an 05 4.8L Sierra with 293k miles. The last few weeks my truck has had a bit of a rough idle but runs fine other than that. Then my engine light flashed a few times which was P0308. I don't have a scanner that shows missfire count but i can say that in the last two weeks of driving back and forth to work 8 miles both ways, the CEL has only flashed once for P0308.

I have swapped coils, wires, plugs, and injectors and it made no difference. I've sprayed carb cleaner around the intake with no change in idle/sound. After fighting with a compression gauge with damaged threads and dropping a plug on the concrete, ground strap down, i finally got to test compression today but the engine was cold and i only tested one side.

Dry tests:

Cyl 8: 140
Cyl 6: 195
Cyl 4: 190
Cyl 2: 215

Cylinder 8 wet test came out at 215.

Fuel pressure with key on was 50, running at idle: 58.

With all that said, this truck burns around half a quart of oil between oil changes (5k intervals)

The compression test seems pretty conclusive that the rings are bad in cylinder 8. Should I give up and accept the fact that this engine is just about done or could there be something else causing the missfire?
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