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Author Topic: Trying to undestand fuel trim banks measurements ME7.1.1 R32  (Read 3542 times)
hummel
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« on: December 17, 2018, 01:27:23 PM »

Hey Guys,

I finally got my R32 running, and mostly without any dtc's, thanks to you guys. But I still struggling with one issue, the two fuel banks is maxing out in trim and the car goes into failsafe. Bank 1 is going rich (-25%) and bank 2 is going lean (+25%) both o2 Sensors is brand new, same kind and fitted in the same spot in the exhaust pipe after the exhaust collector. Originally the sensors is seperated to cylinder 1-3 and 4-6, but I bouight a premade exhaust with room for both sensors after the collector. 

I can simply not get into my head how the two values can be different? How does the ECU know which bank is which when the o2 sensors is in the same spot? Does it even know?? And how can the two signal be different when the sensors is in the same spot? When I delete the dtc's it start regulating again for about 20 seconds and then it goes to failsafe and throwing either P0040  - Sensor signals swapped. Or P3256 Regulation at lower limit Sensor B1S1, and the fueltrim goes to 0%

I asked in other VAG forums but no one where able to help, so maybe someone in here know something and would share it?

Any one?
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nyet
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« Reply #1 on: December 17, 2018, 01:55:59 PM »

You're likely going to have to run a mono-O2 file, which requires ASM hacks (IIRC)

The stereo lambda system is simply not set up to work with two o2s at the same location; their trims will always diverge like that in steady state.
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hummel
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« Reply #2 on: December 18, 2018, 01:09:41 AM »

Thanks for the reply nyet. I think it would be better for me to relocate the 02's into their right position, and thereby allow for both bank to regulate individually.

It is still strange to me that the two 02's can read so different fuel trim, it is almost like their are inverse, ex. one goes to -18% the other goes +18%  Huh  I cannot understand how they can read soo different in the same exhaust spot...

Hopefully I will relocate them later today and see if this helps..
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nyet
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« Reply #3 on: December 18, 2018, 01:18:04 AM »

It is still strange to me that the two 02's can read so different fuel trim, it is almost like their are inverse, ex. one goes to -18% the other goes +18%  Huh  I cannot understand how they can read soo different in the same exhaust spot...

There was a breakdown of this in one of the single turbo threads... I can't recall the technical specifics, but yea, it is odd. It has to do with two different PIDs trying to regulate the same set point. They'll eventually diverge; there is no stable convergence in that control system.
« Last Edit: December 18, 2018, 01:20:36 AM by nyet » Logged

ME7.1 tuning guide (READ FIRST)
ECUx Plot
ME7Sum checksum checker/corrrector for ME7.x

Please do not ask me for tunes. I'm here to help people make their own.

Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience.
gt-innovation
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« Reply #4 on: December 18, 2018, 04:56:31 AM »

Thanks for the reply nyet. I think it would be better for me to relocate the 02's into their right position, and thereby allow for both bank to regulate individually.

It is still strange to me that the two 02's can read so different fuel trim, it is almost like their are inverse, ex. one goes to -18% the other goes +18%  Huh  I cannot understand how they can read soo different in the same exhaust spot...

Hopefully I will relocate them later today and see if this helps..

It has been discussed a lot in the past. There are 3 ways to do it over asm patches and one way to do it over hardware.

In General Some people are copying over the trims from bank 2 to bank 1 and also the voltage, others are copying te_w and ti_w and some others reset something once in a while with only one instruction at a certain area..

From what i have disassembled over the last years there are also 3 variations of the orginal code that is calculating the trims.
i was able to make that work from 2 out of three but i didn`t had a car locally to test the third variation.

The best and most efficient way is to copy over the trims as PRJ wrote on another thread.In my car this way is working flawlessly.

« Last Edit: December 18, 2018, 07:25:09 AM by gt-innovation » Logged
hummel
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« Reply #5 on: December 18, 2018, 10:41:43 AM »


The best and most efficient way is to copy over the trims as PRJ wrote on another thread.In my car this way is working flawlessly.


This is only the best way if you need to run with one o2 sensor, or your manifold doesn't allow for two to be installed, right? In my head the best would be to fit two sensors, one for each bank, thereby the ecu can fine tune each bank individually.

Back to my problem, I relocated the Sensors and now the values is almost the same and much closer to zero (-3-4%), so it seems like my problem is solved. Thanks for the help..  Smiley
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gt-innovation
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« Reply #6 on: December 18, 2018, 12:56:18 PM »

The hardware solution would be to buy a exhaust manifold that supports dual/stereo lambda and there are 2 in the market.You will still have the same issue after a while if your sensors are installed in the same tube..
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hummel
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« Reply #7 on: December 18, 2018, 11:22:44 PM »

Just to clarify, I relocated the sensor to each bank, so now my manifold supports dual lambda. One sensor in each side. 
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gt-innovation
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« Reply #8 on: December 19, 2018, 03:23:09 AM »

Just to clarify, I relocated the sensor to each bank, so now my manifold supports dual lambda. One sensor in each side. 

It will be fine like that.
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