L86 rough idle
07-25-2018, 09:30 AM
#1
On The Tree
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L86 rough idle
Since moving to Idaho I’ve lost access to a lot of friends with nice diagnostic equipment so I’m having to rely on what the guy at the parts store with the cheap scanner tells me. Earlier this year I bought a 2014 Sierra with the 6.2, it’s great I love it and I’ve already racked up some miles to where the truck now has 124,000 on the odometer. About a week ago I noticed it would hiccup at idle, I didn’t think too much of it until my wife even noticed it and later that day the CEL came on. So I went by a parts store and had them throw a scanner on it and the guy said it was a cylinder 8 misfire. Okay no problem I’ll just grab a new set of plugs and that will be that, not so much. It does seem less noticeable but it is still there none the less. After doing some google searches I decided to ohm out a couple plug wires and they were all pretty close about 3,800 ohms (crazy for such a short wire). Next thing I found on google was potentially a large amount of carbon buildup on the valves because of the direct injection, so I pulled the intake and there was barely any. While it was apart I checked the intake gaskets, and I cleaned the throttle body and MAF and put back together. Again it felt a little better but I can still feel it at idle in gear. My next logical step would be compression test and maybe a coil (is there a way to test the coils?). I’ve read some more serious problems are out there, I’m just looking for some input as to where to go next and any helpful insights.
07-26-2018, 10:04 AM
#2
it could be the injectors. Without scan tools its tough to see what is going on obviously. I am curious if the fuel trims are showing anything funky. I think DI are prone to clogging injectors more than an injector in the intake runner would be.
Does fuel injector cleaner work? It may be worth a shot. I'm not saying this because its a known issue I have seen, just thinking out loud and trying to help.
Does fuel injector cleaner work? It may be worth a shot. I'm not saying this because its a known issue I have seen, just thinking out loud and trying to help.
08-17-2018, 05:45 PM
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I still haven’t been able to fix this yet, so far I’ve replaced all of the spark plugs and that didn’t fix it. The cylinder 8 misfire code came back almost immediately, then I swapped the coil and plug wire for #8 to #1 and it took a couple days for the light to come back on, but it was still cylinder 8 misfire. I checked compression on a few cylinders all that I tested were around 210psi. Spoke with a tech at the GM garage and they suggested replacing the PCV valve, it was only a few dollars so I did and it still wasn’t fixed so then I tried a couple bottles of fuel injector cleaner (I’ve always been skeptical of this stuff but was willing to try it) and it still does it. I know I could just take it to a shop, but I have a baby on the way and can’t afford to spend money on the truck right now. Again any input is greatly appreciated.
08-18-2018, 08:40 AM
#6
TECH Apprentice
Quit guessing and get the right tools for the job. You need GMs MDI with GDS2 software. It's the modern equivalent for your truck as a Tech2 is to mine. Same tool GM techs use at the dealership.
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