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Old 06-04-2014, 03:43 PM   #1
cheever13
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Default A/F learning Confusion

I'm looking for a better understanding on how to diagnose my vehicle. 03 WRX. I bought the car knowing it has issues (for fun, so far it has been! just confused now..) and I've been repairing the car back to health.

Recently I found that the flex joint in my cross pipe had failed, promptly replaced the pipe, cleared the ecu and started logging again. It was very apparent at idle (a/f learning A) things were much better.

Before repair:_after the repair:
A 3.5%______A 0.74%
B 4.69%_____B 0%
C 14.89%____C 14.79%
D 9.38%_____D 6.45%

How is it at idle things seem great but at highway speeds (a/f learning C) the car is adding fuel? Would this be a MAF scaling issue?

I put the car in cruise control then watch a wideband. Seems to go from good (14.3-15.5) to periods when it's not so good (14.5-17.5).
Thank you very much to anyone who can help me understand this.
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Old 06-04-2014, 03:59 PM   #2
nmlittlebigman
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Originally Posted by cheever13 View Post

How is it at idle things seem great but at highway speeds (a/f learning C) the car is adding fuel? Would this be a MAF scaling issue?
Possibly, if you are running an aftermarket intake that you haven't been tuned for.
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Old 06-04-2014, 04:01 PM   #3
nmlittlebigman
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Some good reading here: http://www.romraider.com/forum/topic4899.html

In general though AF Learning can a will change daily. Temperature, humidity, ethanol content of fuel, or simply driving through load/rpm ranges that the ecu hasn't seen since the last reset/flash.

Adding 14 % is definitely outside of the norm though. Like I said an intake without a tune or if tuned for that intake then some other mechanical issue or boost leak.
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Old 06-04-2014, 05:14 PM   #4
cheever13
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OK, I appreciate the link. I did replace the inlet hose, but it was with the same aftermarket hose to begin with so I didn't think that would have a huge effect. I did have to replace an aftermarket intercooler with the stock intercooler due to a crack. I understand that would warrant a re-tune, but I guess I didn't expect that to peg the fuel trim.

Everything else on the intake is unaltered. The car was tuned for all of the aftermarket parts. (Nothing new was added since the tune that wasn't a direct replacement)
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Old 06-04-2014, 05:53 PM   #5
nmlittlebigman
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Originally Posted by cheever13 View Post
OK, I appreciate the link. I did replace the inlet hose, but it was with the same aftermarket hose to begin with so I didn't think that would have a huge effect. I did have to replace an aftermarket intercooler with the stock intercooler due to a crack. I understand that would warrant a re-tune, but I guess I didn't expect that to peg the fuel trim.

Everything else on the intake is unaltered. The car was tuned for all of the aftermarket parts. (Nothing new was added since the tune that wasn't a direct replacement)
I doubt your inlet or intercooler is to blame. Compare your AF Sensor #1(front 02) to your wideband. They should be close and track similarly.

Other than than if could be your maf sensor on the way out. Borrow one if you can and swap it out for a day. Make sure to reset your ecu if you do.
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Old 06-05-2014, 09:48 AM   #6
cheever13
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Unfortunately I don't know anybody else with a Subaru.

I wonder if I have an exhaust leak, possibly between the front O2 and wideband. At cruise the front O2 reads right around stoich where the wideband typically reads ~1-2 leaner.

My next approach will be to change out gaskets around the turbo and up pipe (I already have the gaskets). Then re-log and see if they come in closer. If that's not it then I guess front O2 replacement? Trying to avoid spending money for no reason. Thanks again for your help
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Old 06-05-2014, 10:34 AM   #7
JimmyBoyWRX
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Quote:
Originally Posted by cheever13 View Post
Unfortunately I don't know anybody else with a Subaru.

I wonder if I have an exhaust leak, possibly between the front O2 and wideband. At cruise the front O2 reads right around stoich where the wideband typically reads ~1-2 leaner.

My next approach will be to change out gaskets around the turbo and up pipe (I already have the gaskets). Then re-log and see if they come in closer. If that's not it then I guess front O2 replacement? Trying to avoid spending money for no reason. Thanks again for your help
Older cars it's tends to be a maf Issue rather then o2 sensor. Much easier to replace that anyways.
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Old 08-18-2014, 10:07 AM   #8
cheever13
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Following up on my older post here.

Can pulling enough oil into the intake screw with the fuel trims? Oil would lower octane right? (Causing ecu to add fuel??)

I did a WOT run and found I'm burning oil. There was a cloud behind the car, a friend was following and confirmed it smelled like oil. So I was wondering if pulling oil in would explain my fuel trims.


nmlittlebigman: The AEM wideband tracts similar to the front O2 but is always a little leaner. Wideband is within 12" aft of the turbo. catless uppipe.
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Old 08-20-2014, 09:43 AM   #9
Pickler
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Not to hijack but I have always seen near double digit corrections. I'm on stock airbox so I don't understand why the MAF needs to be rescaled? I mostly get larger negative values in A and it tapers off to zero B-D. I think it's normal.
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Old 08-20-2014, 01:20 PM   #10
nmlittlebigman
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Originally Posted by Pickler View Post
Not to hijack but I have always seen near double digit corrections. I'm on stock airbox so I don't understand why the MAF needs to be rescaled? I mostly get larger negative values in A and it tapers off to zero B-D. I think it's normal.
There is a difference in AF corrections (short term) and AF learning (long term). AF corrections will move around quite a bit. AF learning should generally be +/- 5% across all ranges on a well maintained properly tuned car.
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Old 08-20-2014, 02:34 PM   #11
Pickler
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Originally Posted by nmlittlebigman View Post
There is a difference in AF corrections (short term) and AF learning (long term). AF corrections will move around quite a bit. AF learning should generally be +/- 5% across all ranges on a well maintained properly tuned car.
yes i'm aware of that. my short term is usually around -/+ 2%
long term is ~ -8% at idle and ~ -2% in cruising/load.
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