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Old 09-27-2019, 05:13 PM   #1
Tariq Zainal
Scooby Newbie
 
Member#: 506840
Join Date: Sep 2019
Chapter/Region: International
Location: Bahrain
Vehicle:
2015 WRX STi
DGM

Default 2015 STI - Lean AFR on WOT

Hi guys,

New here, been googling and searching this forum for similar issues but could find no answer and if anything was found it varied depending on the mods...so here I am posting this.

So here are the mods I have on the car:

Kinugawa TD06SL2 20G
AEM CAI
Tomei UE Headers(+ Up pipe)
Nvidia Downpipe
Nvidia Q300 catback
HKS SSQV4
CSF Rad
Process West TMIC
GS BC Solenoid
Crawford AOS
Perrin FPR
AEM 320LPH FP
NGK Iridium One Step Colder Plugs
Perrin Fuel Rails
ID 1050X injectors

So after all that was put on the car, it was tuned, made 400/400, car ran awesome, with no issues. Car idled at 14.6-14.7, cruised around the same, WOT low 11s.

Driving the car on a daily basis, 2-3 days later, the AFR on WOT started leaning out. It increased the more I drove the car, and sat at low to mid 12s(idle and cruising still perfect), at that point the car starts sort of holding back and hesitating under WOT(sometimes). So I checked with my tuner and he said, 1, the AFR isn't supposed to change, 2 come see me and I'll look at it. So I checked in with him, he does his thing and the AFR is back at low 11s, the car drives awesome again.

Driving it another few days, the same thing happens, AFR starts to go up on WOT. I get back to my tuner, he does his thing, AFR back at low 11s and on and on this happened around 4-5 times til he said, I tried everything, the AFR isn't even supposed to change because I turned off the auto correction thing. So he advised me to go see my mechanic about it, so I did and he said everything looks ok. I checked with someone else just in case, also tells me everything looks ok.

It looks like my car wants to sit around 12.2-12.4 on WOT. However, like 1 out of 10 days, it'll drop down to mid to high 11s in lower gears, then once I'm in 4th/5th, it rushes towards 12s. Rest of the days, a quick spike to mid 11s then up to low-mid 12s. Tuner says he's never seen this happen with other STI's he's tuned, similar and different setups.

I've been monitoring my fuel pressure, around 43 at idle. 70 something on WOT. I never noticed any drop or anything weird, WOT FP goes up and stays there.

On a lucky day, a friend of mine had an ECUTEK bluetooth OBDII kit, and we logged some data. My AFR was rather good compared to other days. Please mind that I've never done this before and I had no idea what to log and what not to, so I left it to my friend. I hope its got what you guys might need to maybe determine the issue and help me out here.

https://www.mediafire.com/file/a8315...44-31.csv/file

I also apologize in advance if I'm missing anything, I'm not a pro with cars, and new to this. If I missed anything, please let me know.

Thanks.
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Old 09-28-2019, 04:54 AM   #2
Tariq Zainal
Scooby Newbie
 
Member#: 506840
Join Date: Sep 2019
Chapter/Region: International
Location: Bahrain
Vehicle:
2015 WRX STi
DGM

Default Update

So, installed the OEM fuel pump back, and nothing changed. Everything looks normal but, the AFR still leaning towards 12s.
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Old 02-14-2024, 05:37 PM   #3
holbueb
Scooby Newbie
 
Member#: 537017
Join Date: Feb 2024
Default Same problem

Hi there,
I got the exact same issue that you have/had, but I didn‘t find any solution yet. What was it in the end? Maybe it could fix my problem aswell.
Cheers.
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Old 02-16-2024, 12:31 PM   #4
TurboRev
Scooby Newbie
 
Member#: 463945
Join Date: Mar 2017
Default

So, if your mechanic and those fuel pressure tests aren't showing any issues, it seems like the trouble could be with the sensors or maybe how the ECU's program is handling the fuel for your mods. You should keep logging that data, particularly when the AFR starts to lean out, it might just help you spot what's going wrong.
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