Very high LTFT, over 20% on two banks - Z4 35is

[Peter55]

Hello there,
I'll cut to the chatę - I'm having very high LTFTs, especially after long cruising - nearly every time after long, calm driver, CELs are thrown, usually on both banks. Right now Mixture Control CELs are the only one thrown.

The next day car starts but idle is rough - like there's too much fuel - after coupe of seconds it gets better, after adaptation reset or hard driving the day before, there are no problems with idle.
I've this problem since I've got the car - now I'd like to fix it, especially after my main rod bearing spun and I've rebuilt the motor, but the problem isn't get way.

The ECU model is MSD81

Most important changes to engine:
Wagner EVO 3 IC
Catless high flow downpipes
Vargas GC turbos - after rebuilt - no issues with tchem
Fuel pump overdrive (with kit designer by Hydra Performance)
Vrsf chargepipe with HKS BOV
MHD stage 2+
Relocated inlets
Walbro 525 fuel pump
EKP with new thermopads - no issues there

Things I've done to troubleshoot:
All 4 o2 sensors replaced with new Bosch
Checked and cleaned injectors (index 12), coded to the car - no leaks, now and before
2 steps colder NGK plugs, new Delphi coils
3.5 bar map sensor, coded with MHD
Walnut blast head ports
New rail pressure sensor
ECU checked for damages
Checked other HPFP
Compression test - was fine before and after rebuild

I'm running out of ideas - the only one left is that aftermarket downpipes don't have the beat fitment and I had to used double gasket for one pipe before catback. But honestly LTFTs ale very close, I don't really believe that could be a cause.

If I'm getting it right, high LTFT on both banks could be caused by:
- air leak in intake manifold
- exhaust leak after turbo
- exhaust leak near rear O2 sensors
- faulty O2 sensors
- faulty rail pressure sensor
- faulty TPS sensor

Is there something to log to narrow down possible solution? LTFT x RPM x Lambda?

It seems that the biggest LTFT os measured while cruising.

Thank you

 

[Z4Dude]

I have been having similar problems lately but it happened right after I re-flashed my original tune. Car ran rough and short and Long term fuel trims were acting up and Lambda AFR's were lean ... I went to replace my B2 upstream 02 Sensor and found it basically hand tight ... assume it was letting in air. At the same time I pulled injectors and sent off to Injector rehab for cleaning and regen the Piezo stacks. I tried testing my injectors for leaks but sisn't find them when hooked back up and pump energized ... Not sure this is the greatest test , however as you don't have full pressure and cant see what they are doing at High pressure.


Just out of curiosity ... did your issue just appear out of the blue or was something done prior that started it?

 

[Peter55]

I'm not sure if issue was before I've installed catless downpipes - their fitment and possible leaks could be an issue. I'd like to change the rest of the exhaust soon, so fitment problems should be solved, we'll see if that'd help.
But the problem is on both banks, so something tells me car thinks it has less air than in reality or injects less fuel than it should.
It could be ECU, but I have trouble finding other one for testing.

 

[wheela]

Not saying there isn't a mechanical issue somewhere, but when you say you're running MHD stage 2+, I assume you mean the 2+ OTS tune from MHD? Are there flash time options for larger turbos, or the relocated inlets you're running? Those upgrades will increase the volumetric efficiency of the intake. Since n54 doesn't have a MAF sensor, those mods may throw off the DME's estimation of how much air the engine is getting and therefore throw off your fuel trims (unless the mods are accounted for in the tune).

Also, is there a flash time option for that hydra over drive? I believe that mod may also need some tune tweaks to properly control rail pressure.

Sorry about all the flash option questions - I'm n55, so I'm not familiar with what all flash options they have for n54. Anyway, depending on the answers to these questions I think its plausible these problems could be due to mis-match between your tune and the hardware you're running.

 

[Peter55]

I have the same issues on the stock map, stage 0, etc.
Before engine rebuild and on stock turbos the issue was the same.
There's no MAF sensor, but DME uses MAP and Boost pressure sensor to calculate mixture - and they are not dependent on inlets and turbo size. WGDC would be surely affected, but my issue with LTFT occurs mostly on cruising, where you hardly have any boost.
If I understand correctly HPFP overdrive doesn't need a flash option - the pressure demand is simply met quicker.

My priority for now is exhaust, which is not ideal, there could be numerous leaks or issues with secondary cats.

 

[Jern54]

This is an adaption issue. I would do a full adaption reset and log again. If MHD adaptation reset doesn't fix the issue, then you might need to use INPA or Bimmergeeks Protool.

 

[Peter55]

This is an adaption issue. I would do a full adaption reset and log again. If MHD adaptation reset doesn't fix the issue, then you might need to use INPA or Bimmergeeks Protool.

I did, many times
After first longer cruise issue comes back

 

[Jern54]

make a WOT log and share the Datazap URL.
Make sure to log deceleration as well