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Old 11-09-2022, 12:22 PM   #1
zotethemitey
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Default Help me track down what's causing +15.64 AF Learning 1 on Decel

I have a 2017 STI. Protuned by TPG.

Engine Mods are Cobb Accessport, Cobb SF Intake, Cobb EBCS, ID 1050s, Cobb FPR, AEM 340 fuel pump, Invidia R400 turbo back (catless)

I have been on the same tune for about a year. AF Learn 1 has always been a little high ~10-12 but my tuner said this is normal and to ignore unless it gets worse. Well it got worse. And now because of greenspeed I can't have my tune adjusted so I'm going the other direction trying to find if there is a leak somewhere.

Checked my hoses and hose clamps, took off the intercooler and checked the hose to the turbo, replaced BPV gasket, etc.

I'm not sure what else it could be. I'm going to replace my exhaust gaskets in the next few days but IDK that that could be the cause of anything. If the gasket before the front O2 sensor is toast, could that cause high AF Learning 1?

What else should I check? Any advice is appreciated. I'm still a fairly new subaru owner (~2 years). I have been trying to do as much as I can myself but I'm still learning.

If I can't find what's causing it I'm going to have to take a day off work and take my car to get the intake track smoke tested.
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Old 11-09-2022, 12:31 PM   #2
Jedi03
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how much gas are you giving it while decelerating?
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Old 11-09-2022, 01:36 PM   #3
zotethemitey
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Quote:
Originally Posted by Jedi03 View Post
how much gas are you giving it while decelerating?
Zero. Totally off throttle
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Old 11-09-2022, 03:17 PM   #4
Jedi03
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well that would likely cause it...not enough fuel during decel...others may chime in but i would expect very lean conditions at this time, which is what my ap and widebands have all indicated and is no issue
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Old 11-16-2022, 10:50 PM   #5
siete
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Quote:
Originally Posted by zotethemitey View Post
If the gasket before the front O2 sensor is toast, could that cause high AF Learning 1?
~10-12 all the time even at idle?

Yes, an exhaust leak before the front o2 can cause messed up fuel trims, but I think it would show more around the idle learning range.

I'd pressure test or smoke test the system first, and clean the MAF sensor.
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Old 11-25-2022, 12:04 AM   #6
spoolinsti05
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If the exhaust gaskets arent leaking I wouldnt change them. Could just be a false reading from the o2 sensor. Try unplugging the maf and monitor the o2 readings.

Also check your ground wire at the transmission. And add a ground to the exhaust system. If your mount on the transmission is crudy. Might help.
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Old 11-29-2022, 07:00 PM   #7
subaru_gc8
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you might want to check your turbo inlet that is a pretty bad leak
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Old 11-30-2022, 12:01 AM   #8
a5m
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An exhaust leak past the rear O2 can cause high AF Learning during decel. I recently went through this after installing a new downpipe that wasn't mating with the catback all that well. Finally did a smoke test that revealed a massive leak so used a Remflex gasket that thankfully fixed the issue and the AF Learning is steadily coming down, both on decel and at idle.
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