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Old 02-27-2021, 08:49 AM   #1
UndertoW101
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Member#: 100587
Join Date: Nov 2005
Chapter/Region: South East
Location: Odessa
Vehicle:
2020 STi Ltd
Red

Default High Negative AF 1 Numbers ~-17 20 STI E85

Hello everyone,

I have been having an issue with high negative AF (~ -17) numbers during idle/low rpm driving for quite some time now and it's really been bothering me.

I was hoping to get some advice on what to check/look for from the forum.

Car 2020 Sti ~6k Miles

Mod Info:

AEM 340 Fuel Pump
Cobb 1050 Injectors
Cobb Fuel Lines
Aeromotive A1000
IAG V3 Top Feed
IAG Top Feed TGV
PRL EGR Delete Kit
IAG 3mm Phenolic Spacers
Perrin Red 2.4in Turbo Inlet
Grimmspeed 3-Port EBC
COBB Flex Fuel Package
Grimmspeed Turbo Heat Shield V2
Cobb LF By-Pass Valve
GrimmSpeed Ltd Downpipe (w/ Cat, Black Ceramic
Perrin CAI
Perrin FMIC
NGK IRIDIUM ONE STEP COLDER 2309 SPARK PLUG

I reached out to the tuner and the shop that did most of the installs and basically got some finger-pointing and then was told it's not a big deal....

Observations:

Seems to be a correlation between ethanol content and numbers (the more ethanol the less negative AF)

Log Files on 93:

https://drive.google.com/drive/folde...rU?usp=sharing

Thank you so much in advance for any assistance
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Old 02-27-2021, 12:10 PM   #2
GeoNV
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Chapter/Region: RMIC
Location: Colorado
Vehicle:
2009 WRX
dark grey metallic

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Maybe the maf wasnít scaled at idle low speed?
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Old 02-28-2021, 08:34 AM   #3
UndertoW101
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Join Date: Nov 2005
Chapter/Region: South East
Location: Odessa
Vehicle:
2020 STi Ltd
Red

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Quote:
Originally Posted by GeoNV View Post
Maybe the maf wasnít scaled at idle low speed?
Sounds like a tune issue...he went back through it and did not mention that...but that does not mean much

Thanks for the reply
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Old 02-28-2021, 08:44 AM   #4
K3rm1tth3fr0g
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Location: Seattle, WA
Vehicle:
2002 WRX Wagon VF39
Midnight Black Pearl

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Run a couple more tanks through it to see if it clears up.

If they tuned the car, and you are having issues with their tune, they should resolve them for you. And if you haven't changed anything mechanically since they tuned it, they should honestly do it for free since you paid for a proper tune.

Harass the shop that tuned the car and ask them if it is within a range they are comfortable with and if it is not, ask them to correct it. They will likely ask you for longer data logs to get a better sense of what is happening, those logs are fairly small.

If they refuse to touch up a tune without a good explanation of why the car is currently tuned safely, even after you've documented issues through multiple tanks of fuel, it's time to find a better tuner.

Good luck.
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Old 02-28-2021, 04:37 PM   #5
UndertoW101
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Quote:
Originally Posted by K3rm1tth3fr0g View Post
Run a couple more tanks through it to see if it clears up.

If they tuned the car, and you are having issues with their tune, they should resolve them for you. And if you haven't changed anything mechanically since they tuned it, they should honestly do it for free since you paid for a proper tune.

Harass the shop that tuned the car and ask them if it is within a range they are comfortable with and if it is not, ask them to correct it. They will likely ask you for longer data logs to get a better sense of what is happening, those logs are fairly small.

If they refuse to touch up a tune without a good explanation of why the car is currently tuned safely, even after you've documented issues through multiple tanks of fuel, it's time to find a better tuner.

Good luck.
I got the tune in July of last year.

I am looking for a new tuner in my area.
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Old 03-02-2021, 11:28 AM   #6
spoolinsti05
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Jr tuned TT Sleeved

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A lot of people like to blame the tune or tuner. Id start blaming perhaps an aftermarket item you have on the car such as an electrical device. Causing EMI.. Like a radio ext ext. I'm having the same issue. Didnt do it previously on the same tune. So I'm kinda against saying it's the tune. I believe my issue lays in the wire harness. I've went over everything. Who knows maybe my camshaft or crankshaft has some type of magnification going on causing the issue with that.

Last edited by spoolinsti05; 03-02-2021 at 11:35 AM.
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Old 03-02-2021, 12:26 PM   #7
heiche
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This part that you said is interesting: "Seems to be a correlation between ethanol content and numbers (the more ethanol the less negative AF)"

I wonder if the flex fuel aspect of your tune is working properly? By nature 93 is "richer" and e85 is "leaner", but the flex fuel sensor and tune are supposed to adjust for that. Seems odd to me that it isn't adjusting appropriately.
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Old 03-02-2021, 04:26 PM   #8
spoolinsti05
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Jr tuned TT Sleeved

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Quote:
Originally Posted by heiche View Post
This part that you said is interesting: "Seems to be a correlation between ethanol content and numbers (the more ethanol the less negative AF)"

I wonder if the flex fuel aspect of your tune is working properly? By nature 93 is "richer" and e85 is "leaner", but the flex fuel sensor and tune are supposed to adjust for that. Seems odd to me that it isn't adjusting appropriately.
Gas at the pump can range up to 10% ethanol so it can be anywhere inbeween. Same goes for e85 at the pump can be e50 or e85
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Old 03-02-2021, 05:39 PM   #9
heiche
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totally agree. but a working flex fuel system should adjust to any amount of ethanol and the fuel trims shouldn't swing as wildly.
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Old 03-05-2021, 07:23 AM   #10
UndertoW101
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Red

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Quote:
Originally Posted by spoolinsti05 View Post
A lot of people like to blame the tune or tuner. Id start blaming perhaps an aftermarket item you have on the car such as an electrical device. Causing EMI.. Like a radio ext ext. I'm having the same issue. Didnt do it previously on the same tune. So I'm kinda against saying it's the tune. I believe my issue lays in the wire harness. I've went over everything. Who knows maybe my camshaft or crankshaft has some type of magnification going on causing the issue with that.
It happened directly after the install and tune on my way home. I have not done any other mods that would impact it since.
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