P0302 Misfire, Idles rough, New Plug already Carbon fouled 08 GMC Sier

bensaccount · March 9, 2016

So injector is new, coil pack, wire and plug. Engine still idles rough, still p0302 cylinder 2 misfire, still loud. Is it better than it was? Yes. But I am not sure what to make of this at this point.

rdnkcpa · March 10, 2016

You should look for vacuum leak or something internal in the engine such as a broken valve spring, stuck valve etc. Stop throwing parts at it. I think you are beyond internet diagnosis now.

Let's review, you have essentially replaced all of the ignition parts, Coils, plugs, wires, and a new injector for good measure. How much have you spent so far on parts that have not repaired the vehicle? I still think your compression # is lower than expected.

bensaccount · March 10, 2016

You should look for vacuum leak or something internal in the engine such as a broken valve spring, stuck valve etc. Stop throwing parts at it. I think you are beyond internet diagnosis now.

Let's review, you have essentially replaced all of the ignition parts, Coils, plugs, wires, and a new injector for good measure. How much have you spent so far on parts that have not repaired the vehicle? I still think your compression # is lower than expected.

The internet is just a place to exchange information that the government collects because they have complexes right? I have spent a few hundred but I am sure I won't forget how to do any of this stuff down the road and I have been consulting with mechanics the whole time. I do appreciate your time.

bensaccount · March 10, 2016

So I took off the valve cover and cleaned the push rods and sent some b12 chemtool into the land of the lifters. The push rod hole on the offending lifter was clogged significantly more than any of the other one's. Although the cylinder next to it was second place. Not sure why that area is getting the most junk, maybe someone poured something in with the oil since it is right below the oil receptor? Anyway, decided I will be doing my own oil changes from now on as the filter I just had them replace was missing a bolt on the case I am sure they dropped and just didn't care.

So that lifter also seated higher than the other 7 on the side of the engine I did. They appeared to all be uniform except that cylinder. I am not an expert on the design or operation of the cam shaft so I cannot say weather this is cause for concern, but it is an observation of something that is not uniform in the offending cylinder at this point. Not sure how to post a picture.

Cleaning the cylinder and push rods with b12 did not fix the misfire in cylinder 2.

So I think I should take it apart and check for cracks in the valve spring, as you say Enthusiast, and turn the cylinders by hand to check for any inconsistencies in operation. After that my best shot is to try 2 qts of auto transmission cleaner mixed with 4 qts of the oil for a week or two to try to clean it that way from the other end and then change the oil. After that I am looking at a kit of lifters and a few days of focused labor with a hynes manuel, a camera, and a notepad to ensure smooth flow. If anyone has insight into anything from here, thank you as many of you are much more experienced than I am!