High Positive LTFT when cruising 29E0, 2C31

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
Hi,
I've been chasing this issue for a the better of 2 weeks now.
On cruising my LTFT bank 1 becomes pegged at 20-25% while my LTFT bank 2 is around 10-15%. Applying throttle will cause the LTFT to drop. The weird thing is that on WOT everything seems good except for when i shift. On wot shifts you can see one bank goes lean and the STFT don't seem to do anything.

I got a 29E0: Fuel Mixture and 2C31: Oxygen Sensor Emission Control error code a week ago while cruising on the freeway. Got the 29E0 code recently but it hasnt popped back up as of late. Dont seem safe to me at all.
Would anyone have any insight on what the problem might be? Thhanks

Mods:
Downpipes (4 weeks ago)
Intercooler
Chargepipe
Intakes

Things I have checked:
Reset adaptations, Lamda, o2, throttle, octane
Double checked the o2 sensor position
Primary o2 sensors (They were replaced by the dealer 2 weeks before doing the downpipes so they are new)
Vacuum lines, leak
TMAP AND MAP sensors
Boost Leak, None

Day after downpipe install: 1/7/18
https://datazap.me/u/tanrich/mhd-stage-2-1718?log=0&data=3-13-16-17-21-22-23-24

Pretty bad log while cruising, LTFT1 pegged low and LTFT2 pegged high
https://datazap.me/u/tanrich/log-1517437992?log=0&data=3-20-21-24-25-26

LTFT seem to stay pretty far into the log, timing corrections are definitely from the bottle of fuel injector cleaner.
https://datazap.me/u/tanrich/right-...n-fuel-injector-cleaner?log=1&data=3-20-21-24

Recent log Timing corrections from fuel injector cleaner
https://datazap.me/u/tanrich/log-1517729937?log=0&data=3-25
Multi gear Log STFT dont seem to be doing anything post shit
https://datazap.me/u/tanrich/log-1517729937?log=1&data=3-25
Driving around, LTFT are massively high
https://datazap.me/u/tanrich/log-1517729937?log=2&data=3-21-22-25

Thanks
 
Jun 8, 2017
17
19
0
Magnolia Texas
www.magnoliaautomotive.com
Ride
All kinds'a stuff
Exhaust system leak up near the O2's (within a foot or two), check the downpipe install for a good seal. We usually use our smoke machine to pressure the exhaust system from the tailpipes blocked off with rags etc. With the car on a lift and plenty of light ( a hand held searchlight works best).

At part throttle exhaust system leaks up near the engine will push/pull meaning when it's not pushing fumes out it can and will suck fresh air with plenty of Oxygen back in. This throws part throttle fuel trims lean. At heavy throttle the pressure inside the pipes mean a constant outflow of gasses and more accurate readings.

Give it a look and good luck, hard to see in that area.
Vernon
 

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
Exhaust system leak up near the O2's (within a foot or two), check the downpipe install for a good seal. We usually use our smoke machine to pressure the exhaust system from the tailpipes blocked off with rags etc. With the car on a lift and plenty of light ( a hand held searchlight works best).

At part throttle exhaust system leaks up near the engine will push/pull meaning when it's not pushing fumes out it can and will suck fresh air with plenty of Oxygen back in. This throws part throttle fuel trims lean. At heavy throttle the pressure inside the pipes mean a constant outflow of gasses and more accurate readings.

Give it a look and good luck, hard to see in that area.
Vernon

I see, I’ll double check them this weekend. When I first installed them I checked out for any leaks after turning the car on but I guess I wouldn’t be able to feel a small vacuum. I recall my bank 1 vband not wanting to fit on perfectly however we got it on after putting the vband loosely on and getting the bolt through. Bank 2 vband fit on with no problems.

Since bank 2 seems good, why would the LTFT2 be high for bank2?

For the turbo to downpipe gasket, is it recommend using new ones? I did a quick search before doing it and people said it is usually fine without. Tho at this point it doesn’t hurt using new gaskets.

Thanks!
 
Jun 8, 2017
17
19
0
Magnolia Texas
www.magnoliaautomotive.com
Ride
All kinds'a stuff
Since bank 2 seems good, why would the LTFT2 be high for bank2?

For the turbo to downpipe gasket, is it recommend using new ones? I did a quick search before doing it and people said it is usually fine without. Tho at this point it doesn’t hurt using new gaskets.

Thanks!

If you look at that first file, where one LTFT is high and the other is low, notice that the opposite is true in the STFT. So they are more balanced than what appears at first glance. Because the flow of gasses in an exhaust leak scenario is anything but constant. Due to temp, pressure, velocity, and the size and shape of the opening itself the fluid dynamics are all over the chart. At on throttle position and RPM it may pull more O2 into this or that direction and effect the reading of the near or far O2 reading more or less. It's a turbulent mess, and who knows if it's one or more leaks for either bank in different locations for each. It takes a while of driving like that for LTFT's to settle at each point if they ever will. So in these cases the differences will vary.

As for gaskets I don't know, the forum would be better to study. I haven't worked on this platform that much. I'm speaking from many years of working on just about anything that comes into my shop and I'm not a BMW specialist. I have an N54 but fortunately haven't had to do everything to it yet. But with all the high performance parts I'm accumulated I will soon.

Vernon
 
Last edited:

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
If you look at that first file, where one LTFT is high and the other is low, notice that the opposite is true in the STFT. So they are more balanced than what appears at first glance. Because the flow of gasses in an exhaust leak scenario is anything but constant. Due to temp, pressure, velocity, and the size and shape of the opening itself the fluid dynamics are all over the chart. At on throttle position and RPM it may pull more O2 into this or that direction and effect the reading of the near or far O2 reading more or less. It's a turbulent mess, and who knows if it's one or more leaks for either bank in different locations for each. It takes a while of driving like that for LTFT's to settle at each point if they ever will. So in these cases the differences will vary.

As for gaskets I don't know, the forum would be better to study. I haven't worked on this platform that much. I'm speaking from many years of working on just about anything that comes into my shop and I'm not a BMW specialist. I have an N54 but fortunately haven't had to do everything to it yet. But with all the high performance parts I'm accumulated I will soon.

Vernon
I see, I was under the car yesterday and tightened the downpipe to midpipe flange a bit more and shook the downpipe a bit to see if it it would shift into a good seal. One thing I noticed today is that very light throttle maybe 10-15% that my ltft do drop. LTFT1 at 10% and LTFT2 and .8% while cruising. However at 20-25% the same issue still occurs with the LTFT At 14-20% respectively.

I also notice that at any time my bank1 ltft are about 3-4% higher than my bank2. Is this normal? I assume it’s because different variables will affect each banks differently.

I am going to reposition the downpipes tomorrow and check if the vband flange is completely flush. If that does not solve the issue, what could be a another possibility?
 

Bmwfixerguy1

Lieutenant
Jun 5, 2017
873
288
0
Ride
07 335i MT
Can hurt to check for exhaust leaks but How old are the o2 sensors in the car? If they are anywhere close to 100k just replace your pre cats and check again
 

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
Can hurt to check for exhaust leaks but How old are the o2 sensors in the car? If they are anywhere close to 100k just replace your pre cats and check again

They have about 1.5 months on them at this point so less than 5k miles. I replaced the bank 1 primary since that seemed to be the issue and nothing.

I redid the downpipes however I still see my partial throttle cruising ltft fairly high. I guess I’ll wait till it throws an error code again.
 

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
Car is back to stock, the LTFT are still pegged pretty high. Waiting for the code to pop up this time and see if CPO warranty will cover it.
 

Mrg0721

New Member
Apr 27, 2018
1
0
0
Ride
335iS
Did you ever figure this out? I’m breaking my head right now dealing with the same issue. I don’t want to just blindly throw parts at it.
 

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
Did you ever figure this out? I’m breaking my head right now dealing with the same issue. I don’t want to just blindly throw parts at it.
Replaced secondary o2 sensors, everything works wonderfully now.
 

jyamona

Captain
Platinum Vendor
Nov 7, 2016
1,292
1,660
0
Philly
Replaced secondary o2 sensors, everything works wonderfully now.

Sorry I missed this post, could have saved you some troubleshooting. The rear o2 are used to "age" or adapt the main lambdas. Over time this causes what you have seen. It is unfortunate many people still try and spread that the rear o2 don't do anything other than catalyst check.
 
  • Like
Reactions: RSL

tan_rich

Specialist
Feb 6, 2018
89
18
0
Ride
335is
Sorry I missed this post, could have saved you some troubleshooting. The rear o2 are used to "age" or adapt the main lambdas. Over time this causes what you have seen. It is unfortunate many people still try and spread that the rear o2 don't do anything other than catalyst check.

Yup, I always had a feeling it was my secondary o2 sensors but Wanted to get them replaced under cpo warranty. Every time I would put it back to stock everything would return to somewhat to normal with just my bank 1 ltft being higher(3-4%).

Got tired of it, ordered a set of secondary o2 from fcp euro and put everything back on. I would get the codes every week and would clear it, been going about 3 weeks now and everything is great. Just need to a fuel pump and install the mhd flex fuel now.
 
Last edited:

e92wolf

New Member
Apr 22, 2019
7
1
0
Ride
2011 BMW 335i M Sport
Yup, I always had a feeling it was my secondary o2 sensors but Wanted to get them replaced under cpo warranty. Every time I would put it back to stock everything would return to somewhat to normal with just my bank 1 ltft being higher(3-4%).

Got tired of it, ordered a set of secondary o2 from fcp euro and put everything back on. I would get the codes every week and would clear it, been going about 3 weeks now and everything is great. Just need to a fuel pump and install the mhd flex fuel now.
Im currently dealing with the same thing my LTFT currently pegged around +22 both banks when cruising. When going WOT it comes back down near +3%. Currently ordered some upstream O2 sensors. Hopefully that's all I need but im glad I came across this thread because the rears will be next if the issue is still there. Thank you