2008 Silverado 2500hd 6.0 misfire HELP!

Alan1592 · July 15, 2018

So I recently purchased this 2008 Silverado from auction. It’s a 2008 2500hd 6.0. Has a cylinder 3 misfire.

Swapped the coils, injector, plugs and the misfire remains in cylinder 3.

I did a compression test which showed an accoasional 150psi, but most of the time it would read 75psi after 5 cranks.

Decided to removed the head and sent it out to get rebuilt due to some pitying on the valve and seats. Cylinder bore looked fine and the truck doesn’t burn any oil. Cam lob looked fine in cylinder 3 for both intake and exhaust. Everything in the cylinder head was replaced. Put everything back together and the truck still has a cylinder 3 misfire and remains with an occasional 150psi and now has 90-120psi most of the time.

Im lost at this point and I’m getting ready to throw a new motor in this thing. It idles like crap but runs fine after that with no hesitations even under WOT.

Am I missing anything?

sefiroxx · July 15, 2018

Try switching the fuel injector.

Supreme Pizza · July 16, 2018

Replacing the head is a pretty extreme measure if you have not isolated the exact cause of the problem. Replacing the entire engine seems to be even more extreme. If you are willing to throw that kind of time and money at it, I would recommend just sending it to a diagnostic shop. For a couple hundred bucks, you will have your answer.

Shot in the dark, but I would say that IF you have AFM, then that would be the place to start.

e_schott · July 16, 2018

Ok, first off I'm going to scald you for pulling a head on a hunch...let's actually try to diagnose this thing without just throwing parts and making guesses. So you swapped a known good injector, coil, wire, plug, etc. That rules out the components. However, the control side of those components could have an issue. With the compression numbers that you post, that is likely not the problem however. First things first, do you have any trouble codes and do you have a scanner that can read live data. I can try to help you out if you have that. Second, what's compression like on other cylinders on that bank?

e_schott · July 16, 2018

Sorry to double post, I am not in a place I can look it up trying to go off of memory, can you tell me if your truck has AFM? Look for option codes, I think the two option codes for a 6.0 in that year are LY6 and L76, the L76 being the AFM aluminum block. But do not quote me on that, I am going off of memory and I work on a LOT of these trucks. Let me know what I asked above and if you have AFM or not and I will be happy to assist. Private message me and I will give you my phone number and you can text me.

Alan1592 · July 16, 2018

34 minutes ago, e_schott said:

Sorry to double post, I am not in a place I can look it up trying to go off of memory, can you tell me if your truck has AFM? Look for option codes, I think the two option codes for a 6.0 in that year are LY6 and L76, the L76 being the AFM aluminum block. But do not quote me on that, I am going off of memory and I work on a LOT of these trucks. Let me know what I asked above and if you have AFM or not and I will be happy to assist. Private message me and I will give you my phone number and you can text me.

Sending you a PM right now! Thanks!

Drew95a · September 1, 2022

I have this same problem on a 03 silverado 2500hd 6.0

Wondering what came of yours?

P0306 / P0300

We've pulled and replaced spark plugs, wire set, Ignition coil, fuel injector. Good compression 125 psi. Good spark swapped coils multiple times. Checked for scoring on the cylinder walls none, valves are opening and closing. Push rods are good. Grasping at straws at this point.