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Old 01-28-2006, 01:02 AM   #1
vipernj
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2004 fx35 02 Z06
Beryllium, Millenium Yell

Default Help me figure out why my car is bucking/bogging at certain RPMS!

as the title says... When the car is cold (first start up) it idles around 1400 rpms, and if i blip the throttle slightly it sounds the my car has a heavy cam, it kinda sounds like a vacuum leak. When the car is at NOT and I blip the throttle slightly, the rpms drop from normal 750rpm to about 620ish and it feels like its about to stall, but it doesnt, it just jumps back up to normal rpm range(I can tell by the AVC-R)
Now, when im in 2nd-4th gear, the car sometimes bucks and boggs at like 50% throttle from about 2500rpm to about 4K... it only does it sometimes though.
When im decellerating in 2nd-4th and the rpms are between 2500-4K, and i lightly press the throttle, the car starts bucking/bogging again and sort of jumps very slightly...
My mods are:
VF39
Pinks
header
UTEC
AVC-R
stock airbox
sti tmic
3 inch TBE
Forge BOV
Greddy Catch Can

Like I said, it sounds like a vacuum leak but Ive checked and re-checked all of the connections and have not seen anything wrong. The BOV is not leaking and all hoses are fine. Anyone have any idea of what it could be? Thanks for the advice
neel
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Old 01-28-2006, 03:30 PM   #2
Ryandc
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Not too sure about the bucking while driving but sounds like the idle problems I have been hearing about alot lately. There is a sticky on the service and maintenance forum about cleaning and reattaching the idle air control valve. Maybe that can help.....
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Old 01-29-2006, 12:40 AM   #3
vipernj
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anyone else?
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Old 01-29-2006, 12:57 AM   #4
23b_Rex
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wrb

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how are your injectors working?
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Old 01-29-2006, 01:03 AM   #5
vipernj
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Quote:
Originally Posted by 23b_Rex
how are your injectors working?
they're fine i believe... i havent been able to test them, but there are no leaks at all.. it really seems like a vacuum leak but there is no leak,ya know?
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Old 01-29-2006, 10:08 AM   #6
11secwagon
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How long has it been doing this? and was there a mod that you did prior to this starting...I ask because I had a similar situation when I first installed the AVCR on my 03 WRX. I also had the problem after switching from AVCR to TXS manual boost controller...I switched to manual because the AVCR and stock ECU didn't get along. The TXS was a waist gate issue that was easy to fix. But I see you have UTEC so that may not be the problem. Was just curious if your AVCR was a new mod.
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Old 01-29-2006, 02:11 PM   #7
un_focused
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Default Mis-fire

Now im use to tuning other cars and this is my first wrx but aside fromt he vacuum leak have you considered a bad plugwire or plug or even a mis-fire code in the ecu. Have it checked at like autozone and see what they say. Just a suggestion. Good luck.
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Old 01-29-2006, 10:56 PM   #8
vipernj
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Quote:
Originally Posted by un_focused
Now im use to tuning other cars and this is my first wrx but aside fromt he vacuum leak have you considered a bad plugwire or plug or even a mis-fire code in the ecu. Have it checked at like autozone and see what they say. Just a suggestion. Good luck.
i have a scanner and laptop for the utec... however, when i went to get my inspection last week I showed 4 misfire codes.... This is not related to my problem because these codes were brought about from the UTEC Launch Control and FFS... Could it be the tune? I had is road tuned by Junior, but I dont see anything on the motor or any of the components that could be causing these problems.
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Old 01-30-2006, 04:10 AM   #9
MRF582
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sounds like you need slightly more tip-in enrichment. if bet if you were to log the AFR you'd notice the car is running lean for a second while it's stumbling.

try wrxhackers.com. they might be able to help you with that since there's a big UTEC community there. i actually got fed up of having to deal with the UTEC. i've got a different EM now.
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Old 01-30-2006, 02:29 PM   #10
vipernj
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Quote:
Originally Posted by MRF582
sounds like you need slightly more tip-in enrichment. if bet if you were to log the AFR you'd notice the car is running lean for a second while it's stumbling.

try wrxhackers.com. they might be able to help you with that since there's a big UTEC community there. i actually got fed up of having to deal with the UTEC. i've got a different EM now.
actually come to think of it, my egts do drop slightly if i hold it out... and my stupid useless air/fuel gauge does drop to lean and back to rich when it happens... what does more tip-in enrichment mean?
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Old 01-30-2006, 04:45 PM   #11
MRF582
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basically when you open the throttle quickly there is a sudden rush of air that comes in which isn't measured as correctly as it should. so there is more air going in that fuel. to combat that, every single EM including the stock ECU will have a table for 'tip-in enrichment'

so if the change in throttle is let's say 5% it'll add X amount of fuel on TOP of what is already programmed in. if the change in throttle is 10% then it'll add Y amount of fuel on TOP of what is already programmed in. the tables go up to a certain percentage of change in throttle and have corresponding values for fuel enrichment. I don't think the utec has anything like that.

but there is a way for you to reflash your own stock ECU yourself with a laptop and go in there and change the tip-in enrichment yourself.
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Old 01-30-2006, 08:29 PM   #12
kingtut12
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I think it has to do with the UTEC. I had a bunch of problems with hesitation and bucking due to 50% or so throttle. Had it tuned professionally, twice.

Has it been professionally tuned beyond an off-the-shelf-map?

Sometimes if your throttle position is right at the CL to OL transistion (say 25%), and you keep it there - you can get a more pronounced roughness or hesitation.

Its almost like - you need to be under your TPS point or way above it, Not right at it (which seems to be the position of daily stoplight to stoplight driving.) That was my experience with UTEC. I have since went with different EMS with better luck.

Another thought: Is your BOV recirculating or Atmospheric? Could be an issue if its atmospheric.

Good Luck.
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