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      06-07-2014, 10:19 PM   #1
WhatsADSM
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Odd LTFT Values

Not sure where to post this as there isn't an ECU/Tune specific area.

I just recently purchased a used 2011 E90 DCT with ~55k miles on it. I finally had a chance to move my Bluetooth logger over to it and noticed something very odd right off the bat.

At idle the car was running nearly -30% LTFT! Under a light cruise at say 40 mph then would sit around -18%. While accelerating mildly they would go to around zero. Seemed like the less load (more vacuum) the worse the LTFT would be. The more load (closer to no vacuum) the LTFT would return to normalcy around 0%.

The short term fuel trims were around zero the whole time suggesting the LTFT were really that wacked out.

This normal for an S65 M3? Seems really crazy to me, most OEMs would never let a tune out the door like that. I do some dyno tuning on the side and I would also be ashamed if one of my tunes was relying that heavily on long term trims to dial things in.
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      06-08-2014, 07:03 AM   #2
pbonsalb
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It seems more likely the LTFT were closer to zero and the STFT fluctuating over a wide range.
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      06-08-2014, 08:25 AM   #3
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I'm sure it was the LTFT that were way out there. You could see STFT rapidly moving around (near zero) while the LTFT were solid during that time at -30. So the logger seemed to be reading and reporting the correct parameters. Remember that the ecu doesn't have a single LTFT value but rather keeps a table of these values over rpm and load... since it is possible for LTFT to vary a little bit at different operating points. However in most cars, certainly stock ones, the LTFT will change vary slightly across the various operating regions and will almost always be within +-5%.

My only thought is I am using the Torque app (through my Bluetooth adapter) to access the data. Torque will use the standard OBD-II PID for LTFT and STFT. Possibly the standard LTFT PID doesn't map correctly in the MSS60 and therefore the data I'm seeing isn't really what the DME is using in its calculations? I'm stretching a bit as all manufacturers should support it, but its the only explanation I can wrap my head around. At -30% I'm kind of surprised the car doesn't throw a code for overly rich fuel setup as 30% is getting to the edge of what most ecus will correct for.
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      06-09-2014, 09:53 AM   #4
///Mangler
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Reset the fuel trims and see what happens.

T
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      06-10-2014, 08:55 PM   #5
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Quote:
Originally Posted by ///Mangler View Post
Reset the fuel trims and see what happens.

T
Yea... my plan is to go buy a Ediabas K+DCAN cable and get setup with all the BMW tools.

Once I get that all setup then I'll use INPA to collect the same data and see if its real or just due to using the Torque app (i.e. through standard OBD-II PIDs).

I'll keep the thread up to date once I know more.
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      06-11-2014, 03:52 PM   #6
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Quote:
Originally Posted by WhatsADSM View Post
I'm sure it was the LTFT that were way out there. You could see STFT rapidly moving around (near zero) while the LTFT were solid during that time at -30. So the logger seemed to be reading and reporting the correct parameters. Remember that the ecu doesn't have a single LTFT value but rather keeps a table of these values over rpm and load... since it is possible for LTFT to vary a little bit at different operating points. However in most cars, certainly stock ones, the LTFT will change vary slightly across the various operating regions and will almost always be within +-5%.

My only thought is I am using the Torque app (through my Bluetooth adapter) to access the data. Torque will use the standard OBD-II PID for LTFT and STFT. Possibly the standard LTFT PID doesn't map correctly in the MSS60 and therefore the data I'm seeing isn't really what the DME is using in its calculations? I'm stretching a bit as all manufacturers should support it, but its the only explanation I can wrap my head around. At -30% I'm kind of surprised the car doesn't throw a code for overly rich fuel setup as 30% is getting to the edge of what most ecus will correct for.
Is the BMW ETC "pedal follower based" or torque based?
I find it hard to believe that were that rich too..I think if we were then spark plug fouling, increased EGTs, poor ring sealing would be occuring...maybe it is...I have only been here a year...??etc.
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