car is misfiring on WOT
11-24-2009, 06:45 AM
#1
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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.
11-24-2009, 08:45 AM
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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.
11-24-2009, 10:57 AM
#5
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.
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.
11-24-2009, 11:32 AM
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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
11-24-2009, 03:55 PM
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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!
WOW, change those plugs. stick with oem ones.
11-24-2009, 07:10 PM
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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!
11-24-2009, 09:07 PM
#12
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!
Update: Posted up pics. https://www.cobaltss.net/forums/2-0l-lnf-performance-tech-153/piston-ring-failure-lots-pics-inside-lnf-196631/
Last edited by Stamina; 11-24-2009 at 09:56 PM.
11-25-2009, 08:26 AM
#13
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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.
11-26-2009, 03:28 AM
#14
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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...
11-26-2009, 09:51 AM
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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
.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
11-26-2009, 04:13 PM
#16
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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.
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.
11-26-2009, 04:21 PM
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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.
11-27-2009, 01:51 AM
#19
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
.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.
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.
11-27-2009, 05:06 PM
#20
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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
11-28-2009, 04:14 PM
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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?