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      12-04-2019, 12:04 PM   #1
ajm55
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Air Fuel Ratio disparity between banks

This is my first post on the forum. Lots of useful info here. I'll post pics of my ride soon. Its a 2013 F10 M5 Comp Pack. In the meantime, I'd appreciate some feedback from those in the know about an AFR issue that I've recently detected.

The issue is that when going WOT (and to a lesser extent, when idling and at part-throttle) there is disparity in the bank 1 and bank 2 AFRs.

I can't upload the data log, but the disparate data on a WOT 3rd gear run is illustrated below:


5,000 rpm: 14.4 on Bank 1 14.7 on Bank 2
5,500 rpm: 13.2 on Bank 1 13.5 on Bank 2
6,000 rpm: 12.3 on Bank 1 12.6 on Bank 2
6.500 rpm: 11.9 on Bank 1 12.2 on Bank 2

This is measured on a DashDAQ unit via the OBD. I understand that the refresh rate may be a little slow but there is clearly a pattern - Bank 2 is leaner than Bank 1 and I am guessing that the extent of the disparity is indicative of an underlying issue.

I plan to switch the O2 sensors and test.

Apart from catless down pipes, the car is stock.

The bank 1 injectors were replaced about 2,000 kms back. I had not logged AFRs before then and therefore do not know whether the disparity was an issue prior to their replacement.

I'd appreciate input from anyone who thinks he may know the possible cause/s/
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      12-05-2019, 06:58 PM   #2
allmotor_2000
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This level of difference is minor. Keep in mind that this is a cross-bank system so two cylinders from the driver-side mixes with two cylinders from the pass-side (and vice versa).

The system is closed loop and will always try to hit the target lambda. Check where STFT's are. If they are pegged you have different issues.
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      12-06-2019, 04:59 AM   #3
ajm55
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Quote:
Originally Posted by allmotor_2000 View Post
This level of difference is minor. Keep in mind that this is a cross-bank system so two cylinders from the driver-side mixes with two cylinders from the pass-side (and vice versa).

The system is closed loop and will always try to hit the target lambda. Check where STFT's are. If they are pegged you have different issues.
Thanks for the feedback. I'll log STFTs as suggested
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      12-06-2019, 07:28 AM   #4
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How many miles on the "primary" or otherwise known as "precat" O2 sensors? It could be as simple as one of them not working as well as the other. Best to replace in pairs and to not exceed 50k on them. I replaced my originals at 60k and there was a noticeable improvement in driveability which means they actually needed to be replaced sooner than 60k. My car is completely stock, no tune.
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      12-06-2019, 07:56 AM   #5
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Quote:
Originally Posted by technician117 View Post
How many miles on the "primary" or otherwise known as "precat" O2 sensors? It could be as simple as one of them not working as well as the other. Best to replace in pairs and to not exceed 50k on them. I replaced my originals at 60k and there was a noticeable improvement in driveability which means they actually needed to be replaced sooner than 60k. My car is completely stock, no tune.
Thanks for this. The car has done 55,000kms. Today we switched the primary O2 sensors and tested - this made no difference. I'll log the short term fuel trims over the weekend as suggested by Allmotor to see if that reveals an underlying issue. I don't know whether the disparity is unusual on these cars. I would guess that not many log AFRs on both banks
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      12-09-2019, 10:03 AM   #6
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I've logged fuel trims (long term and short term) while cruising (part-throttle). I don't know how to upload the data logs but they show this:

The extremes reached on STFTs on both banks range from about -7 to +7. They are not pegged.

The LTFTs are usually about 8 apart. The bank 2 LTFTs range from about -6 to +2 while the bank 1 LTFTs range from about 0 to +8

I have an extremely basic understanding of fuel trims but what confuses me is that I would expect the bank 1 LTFTs to be in the negative and the bank 2 LTFTs in the positive because the bank 1 AFR is richer than the bank 2 AFR. However, the opposite is true. The bank 1 LTFTs are consistently in the positive and the bank 2 trims are, for the most part, in the negative.

Can anyone make any sense of this?

Apologies if this makes no sense and if someone can explain how one uploads a zdl data log, I'll try and do that
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