Engine degradation, misfire, rough idle, whine, CEL, Positrack light

Cg86 · February 2, 2022

Hello,

I have been trying to chase this down for months, with no luck. A lot has gone on so please forgive the long post.

2 months ago - noticed a whine/whistle during acceleration, only when engine was under load, and seemed to be realitive to throttle position vs RPM.

Replaced, bekts, plugs, wires, alternator, CAI

When that didn't work, I took it to my mechanic who told me it was due to a spark plug wire being not seated.

This month - things have gotten much worse. On a road trip, while cruising @ 75 mph the truck shttered (while accelating mostly), CEL came on (flashing), Traction control light. When I got to the next town I pulled over at a gas station. As soon as I stopped the lights went out. After restarting the truck it ran fine, but I had the codes pulled which showed a cylinder 4 misfire.

Replaced - All 8 fuel injectors

Yesterday - while running around in town I noticed the truck start to shtter when slowing to a stop. By the time I got home the engine was running VERY rough, and the CEL (solid) came on. The traction control light did come on also, but would estinguish as soon as RMPs were increased, then turn back on when stopped. Code was fuel trim, Cylinder 6 misfire.

I pulled the valve cover to check the lifters (check for slop in the rocker by hand), which all checked out. I did notice a small leak from the valve cover gasket over the # 8 cylinder. I also swapped some of the ignition coils which yielded no results.

So, anyone have any ideas? I'm just about to witts end, and I have no idea where to go from here.

Again, if you made it this far thank you. Please if you have any ideas or even a guess I'd love to hear it.

HeySkippyDog · February 2, 2022

Might need a top end cleaning, crud buildup on the valves maybe?

Someone will be along shortly to suggest buying a Fürd.

Snowcamo · February 2, 2022

Pull the plug wires and with some sort of abrasive like a roll of sand paper clean the coil plug connector that was misfiring. Mine was corroded. These coil connections are complete garbage. Like small.

CamGTP · February 2, 2022

Time to check compression.

Pinnacle · February 2, 2022

Normal GM operation lol

Cg86 · February 5, 2022

Follow up:

First thanks for the replys.

I was finally able to run down the issue, so I'll give a full recap incase it might help someone else. There will be some assumptions in this, as I have no way yo prove parts of my theory.

Initial issue (whistle, occasional rough running and CEL) was a bad seal on the # 4 injector, hence the misfire and CEL prior to the initial injector change.

Latest issue (barley running at all) was in part my own fault (first time attempting this). Durring the injector swap I somehow managed to completely destroy the # 6 HP Teflon seal. It was very apparent that there was blow by when I pulled them again. I'm not sure how I managed this, as I thought I was being careful, but alas that's what happened.

After pulling all 8 injectors and replacing the HP seal, she seems to be back up and running (for the time being, at least).

So, what I learned. Be very careful and deliberate when placing and tightening the fuel rail. When tightening make sure you do all 4 bolts at the same time (tighten a little, move to the next until at desired torque) Lube the seals with a small amount of engine oil before installing. Make sure your seals are properly seated on the injector. If you don't have the tool to install them you can use 3/8 ID rubber hose and a hose clamp. 4.5in of extension and a stubby 1/4" air ratchet is perfect for getting the last bolt on passanger side out. Be sure to tape the intake openings as soon as you get the manifold off, as all the plastic wire sheathing is very brittle and will fly everywhere.

Hopeful this will help someone.