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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > What can cause fuel trims to not work sometimes?



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      09-16-2012, 11:38 PM   #67
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Quote:
Originally Posted by themyst View Post
Makes me believe there is a bug in the AFR calculation. It's no coincidence a large group of people are having the same issue at once.
It believe the AFR reading is correct. The trim flatlines, then AFR shoots up, car loses power, and then I let off. I think there is some condition (caused by tune) that causes the DME to not add fuel trims.
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      09-16-2012, 11:53 PM   #68
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Quote:
Originally Posted by The Ghost View Post
It believe the AFR reading is correct. The trim flatlines, then AFR shoots up, car loses power, and then I let off. I think there is some condition (caused by tune) that causes the DME to not add fuel trims.
How piggybacks add fuel is to report a leaner lambda to the DME (aka o2 biasing). The issue with this approach is that if you try to add too much, the car will limp due to the perceived lean condition sent out by the piggyback. That limp is the ceiling piggybacks have to deal with fuel limits.

What BMS is doing with the Cobb base flash and Vishnu with their base flash, is to proactively target the correct AFR/scalar instead of having to bump up against this DME limit.

Historically, pump gas with methanol injection proved to be more than adequate for stock turbos with the piggyback fuel approach, however with the new E85 craze, the DME is operating closer to those limits due to the increased flow requirements of E85 thus forcing BMS/Vishnu to stack piggyback with a base flash.
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      09-24-2012, 08:29 PM   #69
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Got an update on this? Same problem here
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      11-09-2012, 10:49 AM   #70
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Had identical issues here

As odd as this sounds (trust me I know it sounds stupid)

Take the car into redline in 2nd... Before shifting to 3rd... Seriously, it solved this same issue for me
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      10-10-2013, 11:07 PM   #71
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Holy bump... What was the fix for these cars? I'm running into the same problems. Maxed +34% fuel trims OL set to 100% and I'm not running any e85 at all. In fact I installed an inline pump hoping it would help. No change. Firmware / maps recently reflashed with no change.
Is this a dying hpfp? Injector?
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      10-14-2013, 10:28 PM   #72
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Quote:
Originally Posted by uniter View Post
Holy bump... What was the fix for these cars? I'm running into the same problems. Maxed +34% fuel trims OL set to 100% and I'm not running any e85 at all. In fact I installed an inline pump hoping it would help. No change. Firmware / maps recently reflashed with no change.
Is this a dying hpfp? Injector?
My car would flat line fuel trims a lot more often when my OL setting was too high. If I kept it under 95 or so, it would not happen nearly as often. At 100% it happened a lot.

This was a long time ago though. May have been fixed, or maybe it's something inherent to the DME. Not really sure. I was never able to confirm this 100%, but it seemed like the problem/solution.
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