AF Learning Changes With Amount of Gas in My Tank??? - Subaru WRX Forum
 
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post #1 of 12 Old 04-28-2016, 06:49 AM Thread Starter
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AF Learning Changes With Amount of Gas in My Tank???

I have yet to find another case like this. 02 wrx, 4eat, stage 2 ots tune. K&N panel filter, STi up pipe, Perrin catted downpipe, no other related mods. DP was used, new o2 sensor when installed withdownpipe 1.5 years ago. MAF has been cleaned more than once and done delicately.

So my AF Learning 1 has always showed me running rich. As low as -8.xx lbut not all the time. Lately Iclve been seeing as low as -11.xx. The weird part is with a full tank it gets as low as -11 and as the tank gets lower the af learning 1 gets higher but now at a half tank its gotten much worse and will stay as low as -10.xx at about 40mph and I wanna say somewhere around 3k rpms.

I have a bad DP rattle against my tranny crossmember and it might be causing a leak from literally beating the exhaust bolts loose. I also get knock events if I drive below 40 mph in 4th gear(overdrive, its a 4eat auto l, remember).

So what the hell is going on? A bad fuel pressure regulator or fuel pump? Bad o2 sensor? I really am lost here. Im very broke right now and have to get my timing belt done before i can get a protune shop to help me. I could never find a boost or vacuum leak but maybe i missed it? I also get a light but consistent stumble if I really get on it and stay on it at higher speeds. Where should I look? Thank you so much in advance. I am concerned.
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post #2 of 12 Old 04-28-2016, 07:01 AM
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you most likely have a vacuum/boost leak. the most typical indication of a vacuum/boost leak is AF Learning #1

RomRaider ? View topic - How To: Recognize and repair a vacuum leak

(copied for easy reading)
If it's not a vacuum leak:

If you have the symptoms above, but you absolutely cannot find a vacuum leak, there next things to consider are in the tune:

* Injector latency too low - this will also cause a high AF Learning #1 A, with little or no impact on the cruising AF Learning (usually the "C" range).

* MAF scaling too low - bad MAF scaling can cause AF Learning values to range all over the place.

* Injector scaling too large - this can cause large AF Learning values, but typically (if the MAF scaling is good) it will cause all AF Learning values to increase together.

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post #3 of 12 Old 04-28-2016, 03:42 PM Thread Starter
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Tha k youfor getting back to me. As I stated I checled several times for boost and vacuum leaks but never found one. Thats not to sa there isnt one. I replaced all the boost control solenoid and a couple other vacuum lines with silicone a while back.

I have stock injectors and an off the shelf stage 2 tune. Are the i jector issues you mentioned only really a problem with upgraded or dofferent injwxtors? What is MAF scaling? Is that only caused by a faulty MAF sensor? I have cleaned mine twice si ce owning the car in dec. 2012. Wouldnt a bad MAF cause me to run lean instead of rich? I have seen my AF Learning 1 go into positive numbers only in the last 6 months but never higher than +2 or so. Its the negative af learning 1 numbers Im worried about. As low as -10.xx and it only stays there at a certain load and rpm. Thank you again for your help.
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post #4 of 12 Old 04-29-2016, 06:19 AM
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the 3 i listed are all tune related.

i myself am still learning how to tune so i dont have any more info but i can try to point you in the right direction.

RomRaider ? View topic - How To: Closed Loop MAF Scaling
RomRaider ? View topic - Maf Scaling

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post #5 of 12 Old 04-29-2016, 01:28 PM Thread Starter
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Thank you Titter. I appreciate your help.
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post #6 of 12 Old 04-29-2016, 06:27 PM Thread Starter
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Could an exhaust leak AFTER the turbo be causing me this grief? My downpipe has been rattling extra hard lately against the trans crossmember. Ive checked to see if its lose at the up pipe and turbo but even if it was leaking tgere, it would probably still feel tight and not move around right?

Could an exhaust leak from the downpipe cause this? I read up on mapscaling but theres nothing Im capable of doing with my Accessport and limited...VERY limited k iwledge of tuning. I am definitely getting the best shop around to protune my bugeye but I gotta get the rest of the money together to get my timing belt and water pump replaced. Im about 1/3 of the way there hehe.
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post #7 of 12 Old 04-30-2016, 06:29 AM
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in theory it IS possible.

technically, if you have a leak after the turbo, you will have less restriction and more flow out your exhaust, thus spinning the turbine blade a little bit faster than it should be and in turn the compressor side will draw in more air than the ECU think it is pulling in... in theory.

in practical application i do not know if this would be true. but if you're at a loss for ideas, i would say give it a try.

its the same principle as when you change your stock exhaust or go catless. you need to tune for a bigger exhaust or a catless exhaust because there is more flow. a leak can potentially cause increase in flow as well so like i said, in theory, it is possible.

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post #8 of 12 Old 04-30-2016, 05:54 PM Thread Starter
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So if that was the case and the turbo is drawing in more air, wouldnt I have problems with running leaner and not super rich?
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post #9 of 12 Old 05-02-2016, 06:24 AM
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yea that does sound like it would run lean if that were the case. but possibly since its actual;y sucking air through the maf the ecu is correcting for it but not correcting for the leak? im sorta just guessing now. as i said, it was only in theory.

still, if its leaking after the turbo. might as well get that fixed if you can.

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post #10 of 12 Old 05-05-2016, 01:16 PM
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Have you tried resetting your ECU? Changes in temp, humidity and elevation will also have effect on your tune. So your car has gotten used to the winter months so it will need to readjust over time. A leak after the turbo usually messes with the 2nd o2 which is primarily for long term fuel trim.

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post #11 of 12 Old 05-09-2016, 11:54 PM Thread Starter
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I cleaned my MAF the Friday before last which I havent done in about 7 or 8 months and replaced the MAF sensor O ring with a tighter fitting one. Since then Ive noticed my AF learning 1 readings are closer to 0, but they are still closely related to how much fuel is in my tank. Full tank, -7.xx. then it gets closer to 0 as the tank goes down. Im not sure if thats some weird thing relating to the fuel sending unit or if I have a leak somewhere thats screwing with the fuel pressure. Any ideas? This apparently is not an isolated phenomenon but I cant find any info on it online because of the way I word it I guess. Ive never heard of a car needing to be retuned for colder and warmer seasons but then again we dont see a huge swing in temperature here in Virginia. It happens very gradually for the most part. Are you suggesting I reset my ECU every winter and summer? Id think that would just be masking any real problems Im having. Thanks for the input though. Its hard to get help on these kinds of things.

This is great you guys are great.
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post #12 of 12 Old 06-03-2016, 09:21 PM Thread Starter
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Hey gang just an update here. I reset my ecu to clean my maf sensor and after doing this my af learning stayed way closer to zero. It still was loosely related to the amount of fual in my tank. Fast forward to now and its happened again. Full tank=AF Learning 1 is -7.03 and goes down as the fuel gauge goes down. Im getting a protune done soon but before then Im replacing a bunch of hoses when I replace ky PCV valve so maybe that will help. Ill keep you posted. Thanks so much for the advice you guys are the best, really.

This is great you guys are great.
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