Calling all help! Strange/unexplainable O2 issues

Need some major help from the community. I have came to the end of my troubleshooting ability and need help. I will include as much info as needed, so I apologize if this is a bit long.

Car:
'10 535i FBO - MHD v8 E30 tune, happened also on the v7 91 tune.

It all started by getting these codes:
2C28 - DME: Oxygen Sensor 2 before cat converter: System Check
2C32 - DME: Lambda Control 2

I have replaced the Bank 2 pre-cat O2 sensor twice now with new ones and these codes came back. The current one came back 3 days after installing a brand new bank 2 pre-cat O2 sensor and checking for any exhaust leaks.

I have swapped from the v8 MHD E30 tune to emptying the tank and putting in 91 and moved to the MHD v7 91 tune and it still happens the same way. Not tune related that I can tell.

Here's what happens (datazap below shows the issue) I will be driving and bank 1 stft will stop reading and will peg at 0. Bank 2 stft will freak out and bounce all over. This will last for about a minute and then the CEL comes on. Then the bank 1 will recover and bank 2 will peg 0 and this will not recover until I turn off the car and restart.

I can clear the codes and it comes back in a day normally, sometimes less. If I clear the adaptations, it will take about a week for these problems to come back.

I am getting new injectors done next week. I have a feeling they may have some issue with this. But I am not sure why the stft's will read 0 when they do work - it only stops completely randomly after the adaptations have been finalized and the same thing will happen like clockwork in regards how it happens (first bank 1 stops, comes back, then bank 2 stops and doesn't come back).

Here is the log that I happen to grab as it was happening (stft's are highlighted):
https://datazap.me/u/rsicks/o2-issue?log=0&data=25-26


Thank you in advance for the help!

E-diagnosing this is going to be very hard but let's see if we can give it a shot.

@TwistedTuning @Tony@Codewerx

Thank you Sticky!

For added clarity, my troubleshooting steps have been:
3 days ago - Changed from E30 mix to 91 and changed tune
1 1/2 weeks ago - New bank 2 pre cat O2 sensor and exhaust leak check
2 weeks ago - New Eldor coils x6
3 1/2 weeks ago - New NGK 5992 gapped at .22 x6
20 some days ago - VRSF DP
1.5 months ago - New bank 2 pre cat O2 sensor

Last post. Good luck!

http://www.n54tech.com/forums/showthread.php?t=46890&page=2

Damn that’s a treasure trove. I’m not sure how I didn’t come across that as I’ve been searching for about a month and never saw this. Thanks Quattr0, I’ll give this a shot and update after!

I got PhD in AI so that might explain....

Just kidding :D

See this sort of problems often when fuel is changed.

Stop changing O2 sensors.

- check for exhaust leaks. Do a smoke test. Pump it in from the tailpipes.
- swap the b1 and b2 injectors around. Remember to code the injectors and reset adaptations. Then go wot around and see if the problem switched banks.

Quote:

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Originally Posted by Tony@Codewerx

See this sort of problems often when fuel is changed.

Stop changing O2 sensors.

- check for exhaust leaks. Do a smoke test. Pump it in from the tailpipes.
- swap the b1 and b2 injectors around. Remember to code the injectors and reset adaptations. Then go wot around and see if the problem switched banks.

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Thank you for the feedback Tony!

I had a rear bank 2 sensor sitting in my garage, so I slapped it in since it was there. I checked the exhaust while I was down there and re-fitted and re-tightened everything. I've been running E30 for over a year, so I only changed it to 91 per my indy asking me to try it, but the symptoms followed even with the gas/tune change.

I am getting new injectors from the recall on Tuesday, so while its there - we are going to smoke it as well per your recommendation.

So far the car seems to be running better since the rear O2 was installed, but I still have a couple more days before the adaptations are set. That's usually when the weirdness happens.

Fingers crossed that its either the previous rear O2, exhaust leak or an injector(s). All 3 of those are something that can be done right away.

If you haven't changed the post cat O2 on that bank, I'd do that. 2C32 came and went for me after I swapped the post cat O2. I also had a trimming control code with mine. It caused readings on the primary to do all kinds of crazy things. I also swapped my primary O2s and that didnt resolve it.

Quote:

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Originally Posted by mj6234

If you haven't changed the post cat O2 on that bank, I'd do that. 2C32 came and went for me after I swapped the post cat O2. I also had a trimming control code with mine. It caused readings on the primary to do all kinds of crazy things. I also swapped my primary O2s and that didnt resolve it.

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Yup, sure did. After Quattr0's find - I had a post O2 sensor in my garage collecting dust, so I put it to use. Since I popped it in I haven't seen a CEL or weird STFT's. I am still having the injectors done tomorrow, so while I am in there my mechanic is going to smoke test the exhaust as a precaution.

I appreciate all the help from Bimmerboost. I think you guys were on point with the solution.

Quote:

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Originally Posted by RSicks

I appreciate all the help from Bimmerboost. I think you guys were on point with the solution.

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And here I am to take all the credit.

JK it's a really amazing forum when distilled to its bear essence of enthusiasts doing enthusiast things.

Okay so update (because I hate threads that abruptly stop with no conclusion).

A ltitle over a week has past since the car was in shop for injectors. Quick timeline was:

Replaced the pre cat O2 sensor bank 2 (twice) per the codes pulled and checked the downpipe fittings. STFT's were still shutting down while driving.

Replaced the post O2 sensor on bank 2 per quattr0's find (I will come back and rep once I have the ability). The STFT's stopped doing the weird shut downs on each bank.

Dropped her off at my indy for injectors and exhaust leak check. No leaks were found, however the injectors were pretty bad - some leaking, some weird spray patterns. Noticed how well the car performed leaving the shop immediately.

Refueled to E30 and MHD tuned, now the car is running like a champ. So it looks like it was in fact the rear O2 that was causing all the weirdness... the injectors were just a plus. LT and ST trims look great now.

...Now if I can find out why my fuel low pressure sensor sits at 90psi at idle. The N54 keeps you on your toes :rofl2: