Multiple cylinder misfire on 1,3,5,7 and traction light

[Brownie808]

I've been trying to diagnose this problem with my 2007 Yukon Denali 6.2 Liter. Immediately after starting the truck up, catastrophic misfires start to happen. It's a very rough idle with the traction light popping up along with the engine light blinking. The codes that pop up are: P0301, P0351, P0353, P0355, P0357, P0171. So far, to diagnose that problem I swapped coil 1 with 2 to see if it was the coil but the same misfire code still popped up for that cylinder 1. I then changed the coil wire harness as well as the spark plugs and wires for that driver side. It ran fine for a day then the same problems started to occur. At this point it seems like a wiring problem. Not too sure what to do next.

 

[Foggy]

I would suspect bad wiring/ loose grounds on the driver side.
Those are all driver side cylinders.
SO you may have an issue in the wiring harness going to the injectors, coil packs
on that side
May be as simple as a loose or missing ground. There should be
a ground that goes to the back of the driver's side cylinder head

Your stabiltrack codes are due to the misfires. Once you fix that you can clear
it all out

 

[Brownie808]

I would suspect bad wiring/ loose grounds on the driver side.
Those are all driver side cylinders.
SO you may have an issue in the wiring harness going to the injectors, coil packs
on that side
May be as simple as a loose or missing ground. There should be
a ground that goes to the back of the driver's side cylinder head

Your stabiltrack codes are due to the misfires. Once you fix that you can clear
it all out

Okay will definitely look into this! Thank you

 

[rdezs]

You have to look at the big picture as to how the grounds go. Battery cable grounds to the block. Then you have the ground strap from the back of the driver side cylinder head up to the firewall.

So where does your harness get its grounds? On my 6.2, where the battery cable bolts to the block down low on the driver side, there's a second ring terminal which carries ground directly to the front driver side frame rail near the tow hook. Off the negative battery terminal there's also a wire that goes to the ground point under the fuse box.

Then I have another ring terminal connected to ground at the front of the passenger side cylinder head, that goes into the harness. I'm thinking that's the one for the coils and fuel injectors. However, there's another ground coming out of the harness on the back side of the engine, with a ring terminal mounted with one of the bellhousing bolts. It could be that one as well. I would clean and check them all....

 

[Brownie808]

I decided to take in to a auto shop because I'm not a very experienced mechanic myself as I don't have all the tools and workplace to diagnosis the problems. According to them, they ran a compression test and that there was low compression on cylinder 1 causing it to misfire. They insisted this is the root of the problem and that they needed to pull the cylinder to see what the problem is. The estimated quote was $1800 to remove and replace cylinder head with the inspection of cylinder heads. I just don't want to pay that much and it doesn't turn out to fix it. My GMC Yukon Denali has 134,000 miles on it.

 

[rdezs]

Low compression means a mechanical issue. (And keep in mind that might not be the only issue) Pulling the head is the next reasonable step. OMG, the shop prices these days.