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Old 09-09-2012, 10:16 PM   #1
98jdmlegacy
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Member#: 139744
Join Date: Feb 2007
Chapter/Region: NWIC
Location: Belgrade MT
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04 STi
wrb

Default running lean bad at idle, also some in boost

hey ive got an 02 wrx stage 3, turbo, sti tmic, 750cc injectors, walbro, full exhaust, vf22, short ram intake, etc. ive been etuning it the last few months and has been alright. all the sudden my car starting idling really lean like 15.3 afr up to 16. so i replaced the air filter cause it was pretty dirty and reset the ecu. started it now it runs really rough and runs these same afr's. now instead of running bout 11.5 under boost its running 12 to 12.5 which is bad for sure. ideas? wondering if my fuel pressure regulator is goin bad. i checked and cant find any air leaks
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Old 09-09-2012, 11:25 PM   #2
myk
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How long have you driven it since the reset? Also you have any way to pull assume data logs?

Aside from the regulator you could swap out the fuel filter to since that isn't that pricey.

Could also be your primary o2 if you still run open loop fueling.
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Old 09-09-2012, 11:29 PM   #3
98jdmlegacy
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i swapped the front o2 with another one i had tonight and ran it for a few minutes. havent driven that much since the reset. so maybe just drive it more and hope it settles out? i got a new fuel filter bout a year ago. guess its something i could try
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Old 09-10-2012, 01:58 AM   #4
TwoFifty
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The ecu does take a fair while to relearn it'self, Im not sure if that would effect the afr or not but it could be possible?
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Old 09-10-2012, 02:10 AM   #5
FXTRunner
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Did you do a boost pressure test?

I also had a lean condition pop up. Turned out to be the vacuum line that connect to the a port on the side of #1 cyl. intake runner. It sits right under a ground strap there.
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Old 09-10-2012, 05:29 AM   #6
jaxscuby
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reset ecu, disconnect negative terminal and press the brake.
reconnect battery.
let car warm until coolant fans kick on.
go for a drive and verify afr's

if the idle afr's should range from low-mid 15 to high 13.
yes it should be 14.7, but depending on how accurate the
O2 sensor is.

no WOT pulls until you verify the AFR's unless you want to
damage, possibly replace the motor.
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Old 09-10-2012, 12:42 PM   #7
wrxlaunch
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12 seconds at a time

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Op how are u monitoring the af ratio? Jus asking cuz my aem reads 10.4 and my ecu after logging reads 11.2 at wot for the same pull
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Old 09-13-2012, 04:54 PM   #8
98jdmlegacy
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using an wideband gauge thats been very consistent. still looking for answers. no leaks anywhere that i can find
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Old 09-13-2012, 05:00 PM   #9
wrxlaunch
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02 , Vf43 Inside..
12 seconds at a time

Default

Check your fuel trims and see what is goin on with it... Your idle af is good. It's the low 12's at wot that you should look into. You may have a very small leak that will only get bigger over time.

Last edited by wrxlaunch; 09-13-2012 at 05:16 PM.
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