car is misfiring on WOT
 

My car just started misfiring on WOT and threw some CEL's, i used onstar to read the codes and it was the misfire and also an emissions control thing,.. but i have no cat and am not sure if i have that code disabled in hpt or not. any idea's of what's wrong? it runs perfectly fine on normal driving conditions, just WOT past like 4k it really sputters out. i am gonna look at it as soon as i get a chance but my hunch is coilpack or bad sparkplug. any other suggestions are welcome and i can get specific CEL codes later today.. i tried fefilling with a new tank of gas and it was the same thing, so i've eliminated bad gas as a problem.

I'll put $ it's a spark plug. how many miles on the tune? have you changed plugs yet since you've been tuned? Go with OEM plugs and replace them every 5k if tuned.

Is your car fully warmed up before you go wot? If it's not then that's your problem. Our cars misfire like a bitch if they're not warmed up properly.

I had the same problem and I had to have a head replaced?

I had the same problem. It would come and go after driving on a long trip and idle would sometimes fluctuate. New spark plug and coil pack helped for a while, but it ended up being a piston ring had snapped due to cracks in the piston forming because of a manufacturing defect and oil was getting by. Didn't even show up on a compression test until I was smoking. The spark plug on the affected cylinder had oil on it when it started smoking.

If the plugs look fine, try moving the plugs to see if the misfire follows it and maybe think about replacing the pack on the affected cylinder, and just keep an eye on it.

Did you make cam changes recently in HPT? Ive messed up before and entered the number manually and it was + instead of -. Runs a lil funky if you make that mistake :p

Oops...You have a PM. :)

thanks for all the help! i sure hope it's not a cracked ring... but i've been tuned for almost 10,000 miles, have almost 19000 on the car and have never replaced the plugs. i'm away from home now and will be heading to autozone now to pick up some plugs, and hope they let me borrow some tools. thanks again!

:eek: WOW, change those plugs. stick with oem ones.

i just changed them, car seems fine so far, but WOT runs aren't the best cause it's raining and my tires spin to much, even at 70-80mph

I ran 15,000 miles on my tune and 5,000 more miles on stock tune before that before i changed my plugs. Never had a misfire. Just thought it would be good as a preventative. Every 5000 miles seems a little ridiculous but 10,000 miles would probably be a good idea

Yeah, I didn't mean to scare you or anything, but it was sounding like my case. Tuned TCs seem to eat spark plugs. I had ~25,000miles on mine without changing them and up until that point hadn't had any issue. If you start seeing oil on your spark plugs when you take them out next time then I'd start getting worried. My plugs seemed fine until I started smoking and then the affected cylinder's plug was covered in oil when it was taken out the next time.

Update: Posted up pics. https://www.cobaltss.net/forums/2-0l-lnf-performance-tech-153/piston-ring-failure-lots-pics-inside-lnf-196631/

yeah, my plugs all looked the exact same kinda dark golden brown, didn't look worn at all. all i know is that if i do have a cracked piston/ring, i'll be going to wiseco pistons if the dealer doesn't warranty it.

well, it still misses on WOT close to redline.. i'm going to try switching the coilpacks around to see if that changes the cylinders it misses on, (#4). If it doesn't, then compression test which i'll probably do anyways...

I'm guessing the codes you threw were p0300 and a p030x where x is the cylinder that misfired? The first code is raised after numerous misfires are "detected" as it could be damaging to the cat and your emissions would therefore suffer, etc. This is just a guess, but these are the two most common that get raised together :).

Read post #22 at the following link from Bill; if this is ONLY occurring at WOT during a NLS chances are you're not misfiring at all:

Clicky Here

this isn't even during shifting.. last night i was in 2nd gear at about 40 and tromped on it, and all it did was sputter then later on after about 20 miles it seemed fine, although i didn't get it to redline. there is a definite performance loss with my misfiring.. i need to get a compression tester and see if everything checks out there, i'd really like a leakdown tester, but i do not have one.

a few things i did notice are that it does build and hold full boost, but just doesn't seem to make power with it like it did before my misfire issues. and sometimes it's not hardly noticeable and sometimes it really is. kinda random.

Yep, then it's time for a compression test just to be certain. If there's an audible spluttering then no doubt it's a true misfire and not data being skewed.

yeah, it sounds like crap..

Mine would stumble on NLS at first and on long trips it would misfire-sputter under high RPM or high throttle. The CELs only showed on NLS sometimes (flashing) and never during the sputters for some reason (I ended up getting the solid CEL for it much later). The sputter sounded like a quiet version of the "jack-braking" or "engine braking" that semi trucks do. Driving it around town would fix it, and doing repeated runs up until sputter would fix it quicker for some reason. Even resetting the ECU would fix it for a while sometimes (a friend with this same problem just fixed his long enough to get home this way). I didn't have this issue though after new spark plugs and coil packs (later piston ring issues aside) so you're on the right path so far I think.

my car sounds like it's doing the exact thing yours did. same with your engine brake type sound that it'd sometimes make when flooring it.. i went to napa to look for a new coilpack and they didn't even have my engine listed as an option..wtf.. oh well

Everywhere I look online (GM oem parts) shows the same ignition coil for the 2.0, 2.2 & 2.4l engines.

I have a spare coil pack... off an lsj. its perfect but needs the rubber boot that fits over the spark plug.

PM me if you need it...

well, i swapped the #3 and 4 coilpacks and i've still got a misfire in #4... so i think i eliminated the coilpacks. around 6200rpm it sounds like it's hitting a limiter, but will still rev out to 6800, just slowly. it also has 1.5-2.0 degree's of KR at that point too.. not enough to matter to me. but my fueltrims are way the hell off for some reason. My maff correction is off by 22% in some areas where it was was only off by a few percent before. think my O2 sensor could be causing my problems? it has been getting colder out, think this could affect my car's tune enough to be causing all this?

it could. depending on how the afr is set up. would help to know the actual afr you are seeing...
if the fuel trims are lean by 22%, then that would def be a tune issue causing your misfires.

what does your #4 plug look like?

Look for a boost or intake leak if your LTFT's are off that much. Mine drifted around 2% since it dropped into the 30's here.