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Discussion Starter · #1 ·
I'm in the process of tuning my vehicle.

I'm reading values for AF Correction dipping into the high -28 to +26. AF Learning maxes out at -8 and +10.

AFR is steady at 14.75, 22 off throttle.

Tuner diagnosed it as vacuum, boost leak, water in MAF extension, or intake filter positioning. Rechecked all of this, replaced all the parts except MAF sensor.

Cobb Big SF
Catless Turboback Exhaust
Boomba BPV
GS TMIC
GS Charge Pipe
DW300 FP
IAG AOS
Accessport
Turbo Inlet Pipe
Killer B Headers

Car runs absolutely fine, but I can't get over the fact that my AF Correction is so off. I did 3 smoke tests and found no leaks. Could it be a vacuum line on the BPV/Inlet? I'm going to be taking it apart tonight.
Just need a few more ideas on what to check before I start swapping in my stock parts.

Thanks!
 

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You should be referencing your AF Learning (LTFT). AF Correction (short term fuel trims) are not a great parameter for diagnosing vacuum leaks as they vary quickly.

If you confirm that your LTFT is normal (between -10 and +10%) and your DAM remains at 1.0, then I doubt you have any vac. leak of clinical significance.
 

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Discussion Starter · #4 ·
You should be referencing your AF Learning (LTFT). AF Correction (short term fuel trims) are not a great parameter for diagnosing vacuum leaks as they vary quickly.

If you confirm that your LTFT is normal (between -10 and +10%) and your DAM remains at 1.0, then I doubt you have any vac. leak of clinical significance.
I'll try putting the stock intake back on. Thanks for the responses
 

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Discussion Starter · #5 ·
I was very stubborn and ended up buying the Grimmspeed Stealth Intake, but because I have the Perrin Turbo Inlet, that was cut to spec for the Cobb Intake, it couldn't fit. Another expensive lesson learned.

I've had a few professionals assist me in trying to find out the problem. I sent my log/map to Cobb themselves to try and diagnose the issue. Their tech told me that most variables are accounted for(such as DAM, AF Learning, and no knock). So having such a varied AF Correction(-20~ to +20~) is NORMAL?

I asked my tuner if anything else could be the problem(Ron Watson); he essentially told me there was a leak and that there was nothing wrong with the base map he provided.

Went to PRIME MOTORING in NJ, they did 2 smoke tests on my car; left it in for 10 minutes, no leaks as far as they can tell.

So before I reinstall stock turbo inlet/intake, is there anything else I could do/double check, or maybe it is just the intake? Maybe a front o2 sensor issue? MAF sensor? Thanks again
 

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I was very stubborn and ended up buying the Grimmspeed Stealth Intake, but because I have the Perrin Turbo Inlet, that was cut to spec for the Cobb Intake, it couldn't fit. Another expensive lesson learned.

I've had a few professionals assist me in trying to find out the problem. I sent my log/map to Cobb themselves to try and diagnose the issue. Their tech told me that most variables are accounted for(such as DAM, AF Learning, and no knock). So having such a varied AF Correction(-20~ to +20~) is NORMAL?

I asked my tuner if anything else could be the problem(Ron Watson); he essentially told me there was a leak and that there was nothing wrong with the base map he provided.

Went to PRIME MOTORING in NJ, they did 2 smoke tests on my car; left it in for 10 minutes, no leaks as far as they can tell.

So before I reinstall stock turbo inlet/intake, is there anything else I could do/double check, or maybe it is just the intake? Maybe a front o2 sensor issue? MAF sensor? Thanks again
Correct me if I'm wrong, but my understanding is the direct injection engines tend to have radical af corrections due to the nature of how they work.
 

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Correct me if I'm wrong, but my understanding is the direct injection engines tend to have radical af corrections due to the nature of how they work.
Not sure how they would be any more radical than port injection.

The corrections are due to environmental and altitude differences primarily, and secondarily related to fuel ethanol content.
 

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Not sure how they would be any more radical than port injection.

The corrections are due to environmental and altitude differences primarily, and secondarily related to fuel ethanol content.
I'll see if I can hunt down that reference I'm recalling. It had something to do with leaner afr and the fa20 using an actual wide band
 

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I cant find what I thought I read so I'll chalk up to I'm incorrect.
 

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The WBO2 might provide more radical AFR corrections IF the sensor were used during open loop fueling, which it's not.


EDIT: This was a pretty stupidly written post IMO. It would be better to say "if the WBO2 sensor was used in closed-loop mode during middle and high load operation."
 

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Discussion Starter · #12 ·
the fadit20 does come with AFR sensor and a O2 sensor in the j-pipe/down-pipe
Could it just be a problem with the sensors? I tried putting the car under boost and now my AF Learning LTFT is reading 12.50 anytime I'm on the throttle. Confirmed Leak?
 

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are you boosting ok? i think you're fine honestly. you cant go off just one reading esp af learning and corrections,

if anything you should do a 3rd gear wot pull and log it on your ap, monitor the sensors they describe in this thread

https://forums.nasioc.com/forums/showthread.php?t=2828845

post your results there too, im sure someone more knowledgeable will chime in if you got problems. end of the day ask your tuner or some other tuner if you're not happy with their answer.
 

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the fadit20 does come with AFR sensor and a O2 sensor in the j-pipe/down-pipe
The O2 sensor is the "AFR sensor."

This doesn't change any of the previous statements in this thread.

Post a datalog during cruise and we can have a look. My STI LTFT swing between -10% and +14% regularly depending on conditions and fuel ethanol content. Since it sounds like the FA20F O2 sensor can be used in wideband operation (the EJ sensor is also wideband, but the location prohibits the use as a wideband), I can easily take a look at your MAFv calibration -- this is a really good way to look for boost leaks.

What you'll need to do is the following...

Logged parameters: MAF Voltage, Final Fueling Base, AFR, RPM, Throttle Position and Calculated Load; Disable all other extraneous parameters

Take the car out on an EMPTY ROAD. Do a third gear pull through 5000 RPM logging params above.

Load the datalog into a CSV file or a Google Docs file and post here. I'll take a look.

I have mapped a lot of MAF voltage curves over the years.
 

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That's front and rear O2 sensor. That's fine. I can see how you might call the front O2 sensor the "AFR" sensor. The Rear O2 sensor is generally used for catalyst efficiency and light-off measurement

EDIT:
OP, please also add Boost or Manifold Relative Pressure to that list. With a boost leak, it will change the sign of correction with positive MRP.
 

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Discussion Starter · #17 ·
Alright...for anyone still wondering if the problem is still there. Yes...but I did it the right way and brought my car to the pros over at Precision Tuning down in Spotswood, NJ.

Found the issue was between the Boomba BPV and the Perrin Turbo Inlet Hose.
Looks to be a sizing issue. Going to go back to stock inlet.
 

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Did you fix the issue? I just installed the perrin turbo inlet with the boomba bpv and also have the cobb big sf intake. Just did a 3rd gear pull for my tuner and now I have a leak.
 

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Discussion Starter · #19 ·
Did you fix the issue? I just installed the perrin turbo inlet with the boomba bpv and also have the cobb big sf intake. Just did a 3rd gear pull for my tuner and now I have a leak.
Couldn't ever stop that leak. Get a smoke test done and have them ramp it up to 10+ PSI. You'll find the leak and hopefully fix it.
 
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