Rough idle and engine misfire issue

[Jake2588]

So iv been searching here and others places online and can't seem to find a solution, yesterday my engine light came on alone with stabilitrak control service or off message, engine started idling rough instantly so code was p0308 misfire on 8 changed plug and wire no change but the plug i pulled out had heavy black gummy stuff on the arch tip felt oily ....i should mention I just changed plugs and wires a month ago figured I may have damaged one. Well then so i thought maybe the coil pack was out so I switched packs from 8 to 3 to see if the issue would follow the coil ..it didn't... cylinder 8 just doesnt seem to be working what else could i check or am doing wrong?

[diyer2]

Compression check on 8.

Did you use OEM plugs, wires?

Was 8 plug oily/gummy when you changed it a month ago?

Does it use oil?

[Jake2588]

Yes acdelco plugs and wires all plugs looked pretty consistent no buildup and such ....truck does use a bit of oil but not much out of the normal as far as what iv tried iv changed plug,wire swapped coil and just now tried swapping injector to no effect they all seem to work else where. I don't have a compression tool it's one thing i haven't tried is there anything I'm missing? Bad harness maybe or fuse i don't know about?

[MaverickZ71]

Very common problem, unfortunately, especially in the 2007-2010 models with AFM engines. Nothing wrong with Stabilitrak or Traction Control; the DIC shows those error messages due to the misfire being detected. Misfire typically caused by oil fouled sparkplugs due to AFM (engine switching to 4 cylinders under light load) oil usage problem. Piston rings sometimes get stuck with holes aligned and foul the plugs, causing misfire. You can put in a new plug and it may get fouled again immediately. You can read all of the 'fixes' in the "is your truck burning oil" survey pinned at the top of this forum. The quick summary of fixes: the main thing is to turn off AFM asap via Range V8 module or modified PCM tune (like Blackbear), and make sure your truck has the TSB items installed (oilpan deflector and new driver's side valve cover with revised PCV orifice). Be sure to use Dexos1 rated oil, use Top Tier fuel with some Chevron Techron Fuel System (not fuel injection) Cleaner (same as GM's cleaner) sometimes, and consider using something like AutoRx to get your piston rings unstuck. Also consider installing an oil catch can into your PCV system.

[Jake2588]

I checked compression I had zero readings not low but zero is that normal?

 

I'm guessing that cylinder is shot so before I start looking for a new engine or send it to get rebuilt, is it possible that the #8 is part of the AFM and possibly stuck open valves or something not engaging right?

[diyer2]

Valves aren't stuck open or they would hit the piston and destroy it.

Compression zero, BAD. 160 or so normal.

If you plan on keeping this truck, consider a GM engine.

[Jake2588]

Got it that's what I was afraid of well thanks for the help

[Mike GMC]

Pull the valve cover and check for a bent pushrod or broken rocker before you completely write off the engine. If the intake valve is not opening, you won't have any compression.

[Jake2588]

I'll try to check that tomorrow..

Meantime since I don't have funds to dish out for new engine iv been looking online, i can't seem to find many 07-13 but plenty of 06 and earlier shortblocks is that even an option like swaping topends, pulley setups over and such?

[bgbdwlf2500]

How many miles are on your truck?

[Jake2588]

So I took the valve cover off Mike was on the money! The rocker was way loose the bolt was pretty much all the way out, so I went ahead pulled the rocker and rod no visible damage ..could the bolt just have vibrated loose? And would it have caused any damage lifter or something that I should check? Or is as simple as just reinstalling it and done

 

P.s truck has 167k miles

[Bad Bowtie2]

Replace those parts on 8 cylinder. Cheep "try".

 

If not, I would going back with a used 6.2l.

[Mike GMC]

There has to be reason it was loose. Check the treads and consider some new parts and fasteners. At the very least consider some thread locker when reassemble the old parts.