Lean condition troubleshooting

[kevlarblue]

I'm looking for assistance in troubleshooting a lean mixture code: 118010 - Mixture control, cross-bank: Fuel-air mixture too lean.

[Resolved March 2025 with new O2 sensors, see post #13]

It does trigger a CEL about every 100 miles and the car will occasionally have inconsistent idle RPM when cold. Otherwise it runs fine and is reliable.

It is a 2013 M5 with 68K miles:
RK Tunes front mount intakes
CSF charge coolers
MHD Stage 0 Flash
Stock downpipes
Turner muffler delete

I have asymmetric LTFT and STFT - but I am not smart enough yet to know which side is problematic and why. Below is what the MHD monitor is showing at idle RPM. What should these values be? Which side is running lean? What are the possible culprits of the lean condition? What other metrics/tests should I look at to identify where the problem is?

So far I have inspected the MAF sensors and given them a good cleaning. There was a small amount of residue on them but they seemed fine visually. Thanks for any help.

[Bimmer56]

Could be an intake issue pulling too much air measured by maf.
Had similar issue until I reinstalled factory air box with dry filters and problem gone.
BMW is very sensitive to air measurement from maf.

[kevlarblue]

Originally Posted by Bimmer56

Sounds like intake issue pulling too much air measured by maf.
Has similar issue until I reinstalled factory air box with dry filters and problem gone.
BMW is very sensitive to air measurement from maf.

Thank you, I'm considering putting the factory intakes back on to see what that does. But I'm curious why there would be such a difference in LTFT from bank 1 to bank 2 - they have the same intake. A few points different I would understand but it's 50% higher in bank 1.

I'm hoping somebody with more knowledge than myself can chime in on what the fuel trims should be doing in a normal situation. I don't know if 14% and 21% are normal but shouldn't they at least match?

[KurtsM5]

Originally Posted by kevlarblue

Thank you, I'm considering putting the factory intakes back on to see what that does. But I'm curious why there would be such a difference in LTFT from bank 1 to bank 2 - they have the same intake. A few points different I would understand but it's 50% higher in bank 1.

I'm hoping somebody with more knowledge than myself can chime in on what the fuel trims should be doing in a normal situation. I don't know if 14% and 21% are normal but shouldn't they at least match?

Same intake? 2 intakes 2 turbos 2 charge coolers 2 intake manifolds.

[KurtsM5]

Originally Posted by kevlarblue

Thank you, I'm considering putting the factory intakes back on to see what that does. But I'm curious why there would be such a difference in LTFT from bank 1 to bank 2 - they have the same intake. A few points different I would understand but it's 50% higher in bank 1.

I'm hoping somebody with more knowledge than myself can chime in on what the fuel trims should be doing in a normal situation. I don't know if 14% and 21% are normal but shouldn't they at least match?

Before I did that I'd take the intakes off and reinstall. Maybe.you have.a.leak somewhere.

[kevlarblue]

Originally Posted by KurtsM5

Same intake? 2 intakes 2 turbos 2 charge coolers 2 intake manifolds.

Same in the sense that there are identical - I get that it's 2 separate systems.

[kevlarblue]

Originally Posted by KurtsM5

Before I did that I'd take the intakes off and reinstall. Maybe.you have.a.leak somewhere.

I went through all the connections and made sure everything is tight. I found one of the inlets (post MAF sensor) to have a crack in it so I replaced it and that made no change.

[Spacecpe]

Check the PCV hoses. And maybe it’s a good to clean/change the MAF sensors.

[emre019]

There is dirt left in the bank 1in
You need to clean it better
The problem will be solved later

[Blaxwil]

I had the exact same code with some off brand intakes. My indy recommended to put the stock ones back in it and the code went away. Later I swapped out the stock intakes for Project Gamma and still no codes. Fingers crossed.

[Bimmer56]

I experimented with many popular brands of intake.
They all look better, sound better but ended there. I wasn't satisfied with stock filter response either so I kept searching. Best result for me on responsiveness and reliability was stock box with dry filter. Adaptation did not help either. Similar experience with my previous e39, e90, e34.
You can tune out the lean code but that's defeating the purpose.

[SmokinJoe]

I had the same issue that turned out to be the secondary o2 sensor. Changed both and problem went away. Kinda counter intuitive being the secondary o2 sensor usually just measures efficiency of the cats. I think the bmw dme uses a little bit different strategy than others. If you haven’t changed primary o2s that should be done first.

[kevlarblue]

Update:

BLUF: I replaced the primary O2 sensors and the codes have gone away. After resetting adaptations for Lambda Sensors and LTFT everything has smoothed out and my fuel trims are much more symmetric but still not perfect.

Another unsuccessful attempt was new PCV valves (old ones were brittle and likely cracked before I touched them).

I also removed the RK Tunes intakes and put the stock air boxes back on - that changed nothing.

I also had one turbo inlet that was cracked and letting air in past the MAF sensor but changing that out also did not help.

[KurtsM5]

Glad you found it.