LTFT's can someone tell me exactly what they do/why? and why deviation is OK.

OSin456 · 10-10-2006, 08:21 AM

Ok, I've tried to get my mind around this and, I'm just not buying it. Currently I am running LFTF of ~-13%.

So here is my question and I will keep it simple. Lets say on stock fueling I have LTFT's of 0%, gettting great MPG. If I add larger injectors (to the point of driving my LTFT's to ~-13%) and keeping all other things constent, will my MPG and other drivability characteristics be exactly the same, equal to, greater, or worse than they were before.

I understand the ECU "adapts" but if it is constently adapted, it is constently recognizing that it is using too much fuel, no? Meaning that even though it is pulling fuel, there is something constently still present that indicates it to do so.

Also how does it pull fuel, does it simply decrease injector pulse? injector "on-time".

Also, someone car to venture a guess as to how large of an injector you would have to add to stock fueling to creat a deviation. Is it bigger or smaller than I am thinking.

nyet · 10-10-2006, 09:31 AM

if you change around injectors, LTFTs will NOT fix open loop fueling.

also, some information re:correlation between fuel trim and duration

PSmalls::AnalRetentiveNumbNut · 10-10-2006, 09:38 AM

From there, the short term fuel trims can adjust +/-25% to keep your closed loop fueling at stoich (14.7:1 AFR, where you want to be most of the time when not WOT).

So theoretically your closed loop gas mileage should be the same whether your part throttle LTFTs are +13, 0, or -13.

Yes on decreasing injector pulse or "on time" or duty cycle or whatever terminology/measurement you'd like to use.

PSmalls::AnalRetentiveNumbNut · 10-10-2006, 09:40 AM

scalbert · 10-10-2006, 09:43 AM

But according to the supplied articles on wiki, the ECU shifts the trim to 0.0 in open loop. This would mean that open loop fueling is based solely on the programmed maps.

I have seen some ECU's in other makes will, of course, stop updating the fuel trims when going into open loop. But they would use the last stored fuel trim values to adjust the injector pulse width.

Goo to know...

nyet · 10-10-2006, 09:54 AM

again, i would have to defer to other people to tell me if the "last LTFT" value is used after transistioning from closed to open.

very good point and an excellent question.

OSin456 · 10-10-2006, 09:55 AM

My car has an issue then, because mine isn't the same. Mike is going to look at it, if I can ever get in.

PSmalls::AnalRetentiveNumbNut · 10-10-2006, 09:57 AM

LTFTs can change frequently, but by always present I meant they are always affecting closed loop fueling.

PSmalls::AnalRetentiveNumbNut · 10-10-2006, 09:58 AM

The #s change, constant #s at part throttle and constant different #s at WOT IIRC.

nyet · 10-10-2006, 09:59 AM

AND i can't figure out a reliable way to tell what is making it go from closed/open.

its not just load, it seems almost... random

10-10-2006, 08:21 AM	#1
OSin456 AudiWorld Senior Member Garage is empty, add now Join Date: Aug 2002 Posts: 1,084	LTFT's can someone tell me exactly what they do/why? and why deviation is OK. Ok, I've tried to get my mind around this and, I'm just not buying it. Currently I am running LFTF of ~-13%. So here is my question and I will keep it simple. Lets say on stock fueling I have LTFT's of 0%, gettting great MPG. If I add larger injectors (to the point of driving my LTFT's to ~-13%) and keeping all other things constent, will my MPG and other drivability characteristics be exactly the same, equal to, greater, or worse than they were before. I understand the ECU "adapts" but if it is constently adapted, it is constently recognizing that it is using too much fuel, no? Meaning that even though it is pulling fuel, there is something constently still present that indicates it to do so. Also how does it pull fuel, does it simply decrease injector pulse? injector "on-time". Also, someone car to venture a guess as to how large of an injector you would have to add to stock fueling to creat a deviation. Is it bigger or smaller than I am thinking. __________________ ASP Stage 3 Avant <a href="http://www.wunderground.com/US/CA/Hermosa_Beach.html?bannertypeclick=big2"> </a>

10-10-2006, 09:31 AM	#2
nyet Member Garage is empty, add now Join Date: Dec 2000 Posts: 33,095	fuel trims ONLY affect closed loop injector on times if you change around injectors, LTFTs will NOT fix open loop fueling. also, some information re:correlation between fuel trim and duration __________________ ------------------------------------- "It's easier to practice medicine without a license in this country than it is to get info on tuning Motronic." -JasonS9 ECUxPlot - my java based ECUx/VAGCOM/VCDS plotter My hacked version of Flyboy's ECUx template. S4Wiki - CONTRIBUTE TODAY! Web based FATS calculator for ECUx and VAGCOM logfiles Sync your iPod under Linux! Definitive S4 DIY Thread of Doom AWOT Brain Trust #101 AWOT Axis of Evil Member #6 Member, Aw0t Fish Taco Dinner Club I say to you that the VCR is to the American film producer and the American public as the Boston strangler is to the woman home alone." - Jack Valenti, President and CEO of the MPAA this site is NOT for information sharing it's strictly for multiple monologues that result in none of the participants changing their point of view - frank

10-10-2006, 09:38 AM	#3
PSmalls::AnalRetentiveNumbNut Member Garage is empty, add now Join Date: Aug 2006 Posts: 2,688	LTFT means Long Term Fuel Trim...it's is a Long Term adjustment that is always present. From there, the short term fuel trims can adjust +/-25% to keep your closed loop fueling at stoich (14.7:1 AFR, where you want to be most of the time when not WOT). So theoretically your closed loop gas mileage should be the same whether your part throttle LTFTs are +13, 0, or -13. Yes on decreasing injector pulse or "on time" or duty cycle or whatever terminology/measurement you'd like to use.

10-10-2006, 09:40 AM	#4
PSmalls::AnalRetentiveNumbNut Member Garage is empty, add now Join Date: Aug 2006 Posts: 2,688	Wow, it's really coming along Nye. Shame on me for not keeping up to date on your improvements.

10-10-2006, 09:43 AM	#5
scalbert Junior Member Garage is empty, add now Join Date: Oct 2004 Posts: 772	I was curious if this ECU would still use the last set LTFT value even during open loop... But according to the supplied articles on wiki, the ECU shifts the trim to 0.0 in open loop. This would mean that open loop fueling is based solely on the programmed maps. I have seen some ECU's in other makes will, of course, stop updating the fuel trims when going into open loop. But they would use the last stored fuel trim values to adjust the injector pulse width. Goo to know...

10-10-2006, 09:54 AM	#6
nyet Member Garage is empty, add now Join Date: Dec 2000 Posts: 33,095	actually the ME7.1 MIGHT do that. the LTFT article there is from a general source, not ME specific again, i would have to defer to other people to tell me if the "last LTFT" value is used after transistioning from closed to open. very good point and an excellent question. __________________ ------------------------------------- "It's easier to practice medicine without a license in this country than it is to get info on tuning Motronic." -JasonS9 ECUxPlot - my java based ECUx/VAGCOM/VCDS plotter My hacked version of Flyboy's ECUx template. S4Wiki - CONTRIBUTE TODAY! Web based FATS calculator for ECUx and VAGCOM logfiles Sync your iPod under Linux! Definitive S4 DIY Thread of Doom AWOT Brain Trust #101 AWOT Axis of Evil Member #6 Member, Aw0t Fish Taco Dinner Club I say to you that the VCR is to the American film producer and the American public as the Boston strangler is to the woman home alone." - Jack Valenti, President and CEO of the MPAA this site is NOT for information sharing it's strictly for multiple monologues that result in none of the participants changing their point of view - frank

10-10-2006, 09:55 AM	#7
OSin456 AudiWorld Senior Member Garage is empty, add now Join Date: Aug 2002 Posts: 1,084	Ok, I guess I was thinking Short-Term/Closed Loop Trims @part My car has an issue then, because mine isn't the same. Mike is going to look at it, if I can ever get in. __________________ ASP Stage 3 Avant <a href="http://www.wunderground.com/US/CA/Hermosa_Beach.html?bannertypeclick=big2"> </a>

10-10-2006, 09:57 AM	#8
PSmalls::AnalRetentiveNumbNut Member Garage is empty, add now Join Date: Aug 2006 Posts: 2,688	My guess is you're actually talking long term. 032=LTFT, 001=STFT LTFTs can change frequently, but by always present I meant they are always affecting closed loop fueling.

10-10-2006, 09:58 AM	#9
PSmalls::AnalRetentiveNumbNut Member Garage is empty, add now Join Date: Aug 2006 Posts: 2,688	Have either of you logged 032 when transitioning from part throttle to WOT? The #s change, constant #s at part throttle and constant different #s at WOT IIRC.

10-10-2006, 09:59 AM	#10
nyet Member Garage is empty, add now Join Date: Dec 2000 Posts: 33,095	explain more please! AND i can't figure out a reliable way to tell what is making it go from closed/open. its not just load, it seems almost... random __________________ ------------------------------------- "It's easier to practice medicine without a license in this country than it is to get info on tuning Motronic." -JasonS9 ECUxPlot - my java based ECUx/VAGCOM/VCDS plotter My hacked version of Flyboy's ECUx template. S4Wiki - CONTRIBUTE TODAY! Web based FATS calculator for ECUx and VAGCOM logfiles Sync your iPod under Linux! Definitive S4 DIY Thread of Doom AWOT Brain Trust #101 AWOT Axis of Evil Member #6 Member, Aw0t Fish Taco Dinner Club I say to you that the VCR is to the American film producer and the American public as the Boston strangler is to the woman home alone." - Jack Valenti, President and CEO of the MPAA this site is NOT for information sharing it's strictly for multiple monologues that result in none of the participants changing their point of view - frank

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