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Old 02-21-2020, 10:50 AM   #1
JoeRice
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Default Random high afr at cruise

Runs great 99.5% of the time, but periodically get AFRs in the 15-17 range while cruising at 40mph. Last for less than a minute and goes back to normal. AF Correction matches the bizarre AFRs as the system tries to compensate but then stops correcting and starts over. Makes for a cool looking sawtooth ramp of AFR issues. Wondering if anyone has seen similar behavior before?

I don't see any fuel pressure issues or injector issues

Log of issue occurring. If you zoom out you can see that most of log is quite normal with the afr issue occurring at end of log.

https://datazap.me/u/joerice/log-158...zoom=5737-6551

additional note: this issue started not too long after I went to E30, but I don't see where the fuel pump is having issues.

Car: 2019 WRX
Cobb Gen 1 Stg 2 tune with adjustments for TGV del, E30, and EGR del
No cats
Stock fuel system

ty,
Joe
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Last edited by JoeRice; 02-21-2020 at 12:13 PM. Reason: added not
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Old 02-21-2020, 04:19 PM   #2
GlarryHoodDIT
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Cobb Big Sf Intake by chance?
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Old 02-21-2020, 04:49 PM   #3
JoeRice
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Quote:
Originally Posted by GlarryHoodDIT View Post
Cobb Big Sf Intake by chance?
Good thought, but no, it is the stock intake with no adjustments to the original calibration. Not pulling enough air to justify that expense.
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Old 02-21-2020, 04:54 PM   #4
Stretch18
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It's when you let your foot off the gas. Add the accelerator position to the chart and it overlays perfectly.
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Old 02-21-2020, 04:58 PM   #5
gn4rwhals
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Oh you mean this?

https://datazap.me/u/gn4rwhals/weird...-21&zoom=0-439

My car does the same thing, but my pedal is constant. It only does this after I switch fuels, and its so rare I just deal with it, car runs fine otherwise.
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Old 02-21-2020, 05:13 PM   #6
Stretch18
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Quote:
Originally Posted by gn4rwhals View Post
Oh you mean this?

https://datazap.me/u/gn4rwhals/weird...-21&zoom=0-439

My car does the same thing, but my pedal is constant. It only does this after I switch fuels, and its so rare I just deal with it, car runs fine otherwise.
That's the ecu relearning fuel trims, I think.
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Old 02-21-2020, 07:41 PM   #7
JoeRice
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Well, guess I was just being a bit paranoid. Thanks everyone.
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Old 02-21-2020, 08:31 PM   #8
Doughdreads
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My AFR will randomly blip back and forth from stoich to the mid to upper 15's while cruising from time to time. It usually doesn't last very long before settling.

But you're saying you run a modified Cobb Stage 2 OTS map for TGV/EGR deletes and e30? I'm no expert, but if that's the case I feel like that isn't the safest thing to do. I don't really understand why people risk running E without a flex fuel kit or upgraded fuel pump.
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Old 02-21-2020, 08:39 PM   #9
adam99
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Quote:
Originally Posted by Stretch18 View Post
That's the ecu relearning fuel trims, I think.
Could be wrong but I think Gn4r has a flex fuel kit and Joe does not. If that is the case, it could make sense on a flex fuel kit but not if Joe is just switching between a e10 and e30 map. There wouldn't be anything to learn, at least not 15%, assuming your fuel tables are all good. Whats your maf scale looking like compared to stock? Even when the afr is "normal" you consistently have a positive learning and negative correction. Then the correction shoots way up and that's when it goes lean. You should

Double check Maf scale in that load range
Double check Fuel Injector Trim
Go over cobbs Full time closed loop checklist again, any differences can mess up fueling
Changing the lean limit can also effect fueling although I doubt by that much

It is weird that its normal 99% of the time.
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Old 02-21-2020, 09:01 PM   #10
Sillo
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Does it happen while the car is warming up?
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Old 02-22-2020, 07:58 PM   #11
gn4rwhals
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I do indeed have a Cobb Flex Fuel kit.
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Old 02-25-2020, 10:40 AM   #12
JoeRice
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Just circling back to this, been super busy with work, training, and house sale.
No, I'm not running a flex kit, I tweaked the injector trims for e30, but based off Cobbs description of the tables I would still anticipate some positive learning or correction.

I'll go back through the tables again to see what deltas I have from the OTS map in case I missed something in the closed loop section. I did change the learning limits to 40, and now I'm wondering if that wasn't a mistake since they were blank, need to tweak that back.
MAF scale is stock.

Thanks for the replies,
Joe
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