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Hey all, I've got a 2010 Silverado 5.3L (VIN 3) with about 195,000 miles (AFM deleted about 140,000)
Recently I did a tune up and changed all plugs, and about a month later I started getting a rough idle and a cylinder 8 misfire, and a little bit of a tick. When I changed the plugs I noticed the #8 plug was a little hard going in, I was thinking the threads might be a little damaged....uh oh..... But I was able to get it in all the way without applying much force so I figured it might okay.
Well I took it to a shop once I got the misfire and told them what was up. They replaced the coil and wire and plug for good measure (they didn't say they had any issues with threading the plug), and the idle smoothed out some, but a still rough. Another month went by and then I got a cylinder 8 misfire again.
Took it back, they said they heard a tick and diagnosed it is a lifter and gave me my money back.
Next I took it to a Chevy dealership for a second opinion before I condemned the truck. Told them everything that's been done to it, the hard to thread #8 plug, and the diagnosis of the other shop.
Chevy looked it at for 3 days and was inconclusive in figuring out the problem. They said compression was good at about 145 on #8. All the other cylinders were about 147-150. So they ruled out a lifter. Coil, plug, wire all good. Injector ohms at 13.3 along with every other injector. They said they didn't have issues threading the plug or compression tester in.
They said best guess is a clogged injector but no way to tell unless I replace the injector. I do run either sea foam or Lucas through every time I change the oil, every 3,000 miles.
I noticed when looking at it some more, I could see just a little bit of the plug between the wire boot and cylinder head on the 8 plug, but not on the others (although they are hard to see).
I'm debating on changing the injector and putting more money into it if that isn't the problem, or if I should try thread chasing the spark plug hole, but the #8 plug is a real pain to get to. Or is it really maybe the lifter going out? There is a good tick on that bank.
The only code I'm getting is a P0308.
Anybody have any thoughts on this? It's driving me nuts, and nobody can seem to figure it out.
Thanks in advance for any suggestions.
 

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bskaredofpk2 said:
HorizontalHunter said:
Just because wires and coils ohm out fine doesn't rule them out IMO.

I would swap the coil/plug wire to a different cylinder and see if the misfire moves.

Bob
Swapped them all with cylinder 6 plug, coil, and wire and the miss didn't move.
I'm not sure how hard it would be, but do the same with injectors.
 

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hey @bskaredofpk2,
Did you have any lean codes that would have indicate a vacuum leak?
I have a 4.8L and am having the same issue as you (P0308). I swapped injector, coil, wire and plug from cylinder 8 to cylinder 6, and the misfire is still on cylinder 8. But, I do not have any lean, or vacuum codes that would point me to a intake gasket.

Any input is appreciated.
 

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just a quick tech tip I learnt over the years. if you suspect vacuum leak spray that area tou believe to be the problem with intake cleaner and the rmp will increase.
I know this is a old thread but thought I'd throw that on here incase someone else stumbled across it.
Bronson
 
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