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Old 04-24-2014, 08:41 PM   #1
needasubbie
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Member#: 376946
Join Date: Dec 2013
Default misfire under full boost.

2004 wrx
Stage 2.

Car was tuned prior to purchase 302hp at 20lbs. I have owned it for a few months with no problems. Recently the o2 sensor went. Changed it along with plugs and oil. Car drives like a dream unless its in full boost. Feels like a misfire, maybe fuel cut. No check engine light. If I turn boost down below 15 lbs, the car boosts fine. I'm stumped and any feedback would be greatly appreciated.

Thank you
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Old 04-25-2014, 11:03 AM   #2
needasubbie
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Any takers? Need help
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Old 04-30-2014, 10:48 PM   #3
shadow623_
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Member#: 389555
Join Date: Apr 2014
Location: Syracuse, NY
Vehicle:
2005 WRX
Silver

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sounds like fuel cut/boost cut - if thats stock turbo i would keep boost down anyways 20 lbs for the stock turbo is way to high. i would keep it at 15/16 psi max and that should stop your boost cut issue unless you get a open source tune for the 20 psi which as stated i would HIGHLY NOT recommend.
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Old 04-30-2014, 11:22 PM   #4
drifterX2013
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could be caused to improper plug gap or heat range, could be caused by coil pack issues, could be cause by fuel pressure drop under full boost, could be ****ty fuel, could be not high enough octane fuel, could be dirty injectors. more then likely spark related or ****ty fuel related.
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Old 05-02-2014, 11:47 AM   #5
KitchenerWRX
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Member#: 79934
Join Date: Jan 2005
Chapter/Region: E. Canada
Location: Kitchener, Ontario
Vehicle:
02 WRX
MBP

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I would bet it's a combination of improperly gapped plugs and coil packs that are on their way out. Or one or the other on their own.

I experienced similar symptoms. If I were to roll into boost hard, WOT, it would buck/stutter closer to 20psi. If I were to roll into boost at like 60-70% throttle, and only push 14-16psi, it would be ok.

I found out that my plugs were gapped at like 0.035" as well as my coil packs were starting to really fray at the insulation coil portion. The combination of a huge spark plug gap (spark has to travel further distance, and that extra distance requires a stronger spark to actually jump the gap) combined with dying coil packs really didn't like high boost. The spark would just arc/break up and thus creating misfires which is explained by the hesitation/bucking I experienced. A fresh set of OEM coil packs and properly regapping the plugs to 0.028" worked wonders and I could finally hold 21psi on my EVOIII-16G all day.
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