ZPOST
BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   ZPOST > BMW Z4 Technical Talk > Engine, Exhaust, Drivetrain Modifications
  TireRack

SUPPORT ZPOST BY DOING YOUR TIRERACK SHOPPING FROM THIS BANNER, THANKS!
Post Reply
 
Thread Tools Search this Thread
      05-01-2017, 07:57 AM   #1
beaniegti
New Member
6
Rep
26
Posts

Drives: BMW Z4M Coupe
Join Date: Mar 2013
Location: UK/Italy

iTrader: (0)

Z4M- Long term fuel trims-thoughts and ideas please

I recently downloaded and had a play with the OBD Fusion app (great app btw) and noticed my long term fuel trims were strangely high (-17%). From what I can gather this would mean the car thinks it's running rich and cutting (a lot) of fuel.

The car is running alpha-n and an evolve airbox and was all fitted about 18months ago and seems to drive fine but obviously I'm concerned at these trims.

No codes are stored, no real driveability issues but I'd like to get to the bottom of it-any thoughts as to what might be the culprit or what I should do? -perhaps there's a combination of PIDs I can log to give me a clearer picture? This whole data logging and diagnostic work is very new to me so any help and advice would be greatly appreciated!

Thanks in advance
Appreciate 0
      05-04-2017, 06:17 AM   #2
pokeybritches
Colonel
pokeybritches's Avatar
United_States
479
Rep
2,782
Posts

Drives: ESS/G-Power Z4M, VF Z4, 996tt
Join Date: Sep 2009
Location: Los Angeles

iTrader: (12)

Garage List
2006 BMW Z4M  [10.00]
2006 BMW Z4M  [8.50]
2003 BMW Z4 3.0i  [9.00]
Outside of programming the ECU to eliminate hardware errors for running MAF-less, and WOT spark advance / AFR / VANOS / etc., I suspect the tune has been altered in two areas:

1. The ECU has a transfer function for the intake, which should be adjusted any time the intake/sensors are modified.

2. Transient fuel tables, taking into account the advantages provided by the new intake setup.

You can try resetting the fuel trims, and watching your STFT on light load, then abruptly moving to WOT. Odd STFT with constant light load would indicate the alpha-n tune hasn't accurately accounted for the airbox (intake transfer function needs to be modified). If constant part throttle is good, but abrupt changes in throttle result in a high STFT, the transient throttle fuel maps need to be adjusted (tweaking these tables should only occur after confirming the intake transfer function is accurate).

A dyno tune is the ideal solution for either scenario, assuming your O2 sensors are giving accurate feedback. If they are old, I would replace them first to avoid spending big $$ on a tune when it's a sensor issue.
__________________


VF Engineering Z4 3.0i, ESS Z4M, G-Power Z4M, 996 Turbo
Appreciate 0
      05-04-2017, 01:11 PM   #3
beaniegti
New Member
6
Rep
26
Posts

Drives: BMW Z4M Coupe
Join Date: Mar 2013
Location: UK/Italy

iTrader: (0)

Thanks pokey, I appreciate the input

I'll have another play with it this weekend and try to monitor the stft's. As far as I know the O2 sensors are original so may be worth swapping those-is there any reliable way to test them before shelling out?

As for resetting the fuel trims, unfortunately I have no way to do this at the moment. The app I use doesn't cater for this and I have no laptop either. Any thoughts on Ho to go about it?
Appreciate 0
      06-18-2017, 05:44 PM   #4
beaniegti
New Member
6
Rep
26
Posts

Drives: BMW Z4M Coupe
Join Date: Mar 2013
Location: UK/Italy

iTrader: (0)

Sorry for not updating sooner but I've been snowed under with work and forgot about this thread.

I've had a little play with the app again and it turns out to be a little different than first thought. I'm not entirely familiar with it all yet so I'll leave any final conclusions but I'm fairly confident that it was more down to my mis-interpretation rather than a serious issue. The Cayman R I 'met' on the way back from my logging trip would no doubt confirm that the car certainly goes well enough!

I'll continue to play about with it for a while as it's quite a nice thing to fiddle about with but ultimately I'd like to get the car back to the dyno and have a proper custom map made for it as well as getting some expert opinions on the current state of affairs.
Appreciate 0
      06-20-2017, 06:35 PM   #5
Vanne
Down Under!!
Vanne's Avatar
United Arab Emirates
1593
Rep
4,293
Posts

Drives: 2007 Z4MC
Join Date: Mar 2013
Location: Dubai

iTrader: (4)

No doubt, I gotta also add, if your using generic software to monitor events and sensors be carefull. I had myself in all sorts of worry when I was using Android software to monitor some of the elm outputs in my 2013 JKU. Turns out the numbers were incorrect due to non alignment and calibration of software. Lol I can laugh about it now.. make sure your using the right software/hardware.
__________________
2007 EuroSpec Z4///MC - Building/Developing Z4 GT3
Powered by
Appreciate 0
      06-27-2017, 04:57 PM   #6
beaniegti
New Member
6
Rep
26
Posts

Drives: BMW Z4M Coupe
Join Date: Mar 2013
Location: UK/Italy

iTrader: (0)

Yeah, that's a good point-it's a generic program for all cars as far as I can tell and like your stuff, seems to just relay the data from the OBD reader. In theory it 'should' be correct but who knows? I've no way to actually test and verify it sadly.
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 08:13 PM.




zpost
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST