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Old 11-10-2009, 04:11 PM   #1
Scooby Specialist
Member#: 147755
Join Date: May 2007
Location: Cheyenne, WY
2011 CTS-V Sedan M6
1993 Talon TSi AWD

Default Misfire / Stutter only under WOT?

-AP V2 w/custom tune
-TBE / Uppipe
-820cc Modded Injectors
-Walbro 255
-LW Crank Pulley
-NGK Iridium one step colder
-Grimmspeed EBCS
-Yadda, yadda, yadda

Car ran fine for few months after the turbo install and tune, then about a month ago started having the issue it has now. The car runs excellent at idle and just driving around, but once you go WOT it misses and stutters once it hits boost. You can run the car all the way up to redline at part throttle and it pulls fine. When the issue first started to occur about a month ago, it was only a slightly noticable power loss in 3rd and 4th after driving the car for a long time. Now it has gotten bad enough that it just misfires under WOT no matter how long it has been driven. I've tried cleaning the MAF with no change. The plugs only have about 6,000 miles on them. When the car sets misfire codes after an ECU reset, it sets p0302 first and eventually will set codes for all the other cylinders over the course of several days.

So... does this sound like a coilpack issue or do I need to check my plugs? They were gapped at .030 when I put them in.
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Old 11-10-2009, 04:40 PM   #2
Dragon Wagon
Scooby Specialist
Member#: 101095
Join Date: Nov 2005
Chapter/Region: NESIC
Location: the wall
1997 leggy gt
Reo Red


regap your plugs down to .28 and check for cracks on the porcelain part of your plugs dont over tighten them it could cause damage you only need 15 ft lbs tork
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Old 11-10-2009, 04:45 PM   #3
Uncle Scotty
Scooby Guru
Member#: 16200
Join Date: Mar 2002
OK buy Nates beans


boost leak.....if it aint plugs
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Old 11-11-2009, 02:45 AM   #4
Scooby Newbie
Member#: 228932
Join Date: Nov 2009
Chapter/Region: Tri-State
Location: Greensburg Pa
02 WRX


i was having the same prob, i changed my plugs and it went away
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Old 11-11-2009, 03:06 AM   #5
Scooby Newbie
Member#: 161678
Join Date: Oct 2007
Location: Marquette MI
2002 wrx


I had the same problem as well and after trying many things it ended up being 2 things, weak grounds on the heads, and my plugs. I had put in one step colder plugs and they where iridium NGKs. I have read alot that people don't have good luck with the iridiums, and have even more trouble with the one step colder plug. So after swapping coilpacks with some extras my buddy had, replacing my MAF sensor, fuel filter and pump and pressure regulator it came down to the plugs being the majority of the problem. I replaced the iridium one step colder units with stock heat range copper NGKs for 2 bucks a piece and problem solved!!
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Old 11-11-2009, 06:25 PM   #6
Scooby Specialist
Member#: 80012
Join Date: Jan 2005
Chapter/Region: RMIC
Location: Salt Lake City, UTAH
04 BMW M3
Ducati 620 Dark / 08' 848


Could also be a fuel issue... I had the same problem and turns out my fuel pump was bad. Major pain in the ass tracking the issue down.
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Old 11-24-2009, 09:25 PM   #7
Scooby Specialist
Member#: 83924
Join Date: Mar 2005
Chapter/Region: MWSOC
Location: Avon Lake, OH
2005 HTA 86 STi
10.66 @ 136 mph


Im working on an '06 STi that has the same symptoms. I just put NGK +1 colder iridiums in the car as well.. The car was also tuned for stock plugs. Anyone know if colder plugs require any tuning?
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Old 11-25-2009, 12:55 AM   #8
Scooby Newbie
Member#: 161678
Join Date: Oct 2007
Location: Marquette MI
2002 wrx


Not sure they would require tuning but i have heard a few guys say they see alot of misfires from one step colder and also swear by the cheaper copper NGK. These 2 reasons are why i went back to stock heat and copper plugs and i have not misfired in several months now
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Old 02-14-2010, 03:36 AM   #9
Scooby Specialist
Member#: 238300
Join Date: Feb 2010
Chapter/Region: NWIC
Location: tacoma wa
00 2.5rs built
ej255 swap


i have same problem. any luck anyone?
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Old 02-14-2010, 03:12 PM   #10
Scooby Specialist
Member#: 175878
Join Date: Mar 2008
Chapter/Region: MWSOC
Location: Fort Wayne, IN

My experience with NGK Iridium colder plugs has been that they like to foul quicker. On my STI that was running pig rich, I was lucky to get 2k out of the plugs. I routinely took them out every time I changed the oil to clean them. Switched to stock heat range coppers and got a lot more mileage out of them.

I also had the same issue that you had at one point after doing a compression test. Apparently when putting one of the plugs back in afterwards, it must have got bumped and the gap was off just a little bit. Replaced the plug with a new one with the correct gap and it eliminated the stutter/popping at WOT.

Don't even mess with trying to re-gap the iridiums, they get ruined when placing a gapping tool into them. I recommend switching to a standard heat range plug (my personal new favorite plug is the Denso Platinum TT's @ $1.99 a plug at Advance Auto Parts), check the gaps ( 0.27-0.29 I believe), reinstall, and go for a drive.
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Old 03-03-2010, 12:35 AM   #11
Scooby Newbie
Member#: 240032
Join Date: Mar 2010
Chapter/Region: MWSOC
Location: Iowa
2010 FXT


I have basically the same problem on my 08 STI but mine only starts to stutter/misfire/rev limit after I go past 5,000 rpm WOT. Seems to be most noticeable when in Sport Sharp. It only just started happening about a month ago. It's been sub freezing temps for the whole time so I'm not sure if that has anything to do with it. I've ran 2 bottles of heet through the system and I only use 91 or 93 octane. I take it into the shop in a few days.
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Old 03-03-2010, 12:47 AM   #12
Scooby Specialist
Member#: 236092
Join Date: Jan 2010
Chapter/Region: NESIC
2004 wrx full exhaus
vf48 aps big tmic nstuff


what kind of 20g?
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