I got a question about LTFT. currently my car is tuned to stay with -7 and +16 LTFT throughout the entire range of rpm and boost. well, i was looking at some of the graphs and every place where I am at a steady rpm and then I gun it I find my LTFT goes from -3 or -4 to +16. this would lead me to believe that when I gun it more air is forced in and the ECU has to compensate to richen things up. after this initial richening it drops to like +6 an levels out. Now the thing i want to know. Is this normal? thanks James
#28916, "RE: datalogging and LTFT" In response to Reply # 1
i beleive the only way the LTFT can jump like that is if the STFT is already maxed out. Sounds to me like it's doing some major compenastion for a lean condition.
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#28918, "RE: datalogging and LTFT" In response to Reply # 1
>Whats LTFT?
Long term fuel trim..
Basically it's a factor that the ECU uses to determine the overall general fuel curve the ECU needs to provide at each rpm and load, based on the standard curve programmed into the ECU before taking into account the current engine needs.
STFT - Short term fuel trim
The amount of correction needed to maintain *current* safe operating fuel ratios..
Basically, tune for STFT then pay attention to LTFT.. if your STFT is showing a +25 and your LTFT is showing a +25 your probably WAY too lean..
If STFT is showing a -25 and LTFT is showing a -25 then your probably WAY too rich.
If your STFT is showing close to 0 (+/- 5 or so) and your LTFT is between -5 and 0, your tuned up just about perfect
Always tune a bit rich, just for highway cruising.. i remember reading somewhere that the ECU will advance timing *AND* lean out after a steady constant operating RPM (ie on the highway).. if you tune right on the edge of lean (power) then your riskin going too lean when your cruisin..
ttyl
WheatKing
-- DSM Junkie -- 4 - 1G talons 4 - Avenger/sebrings 1 - Jeep to tow em home when they break
#28919, "RE: datalogging and LTFT" In response to Reply # 4
i also noticed that when i floor it my ltft goes to +17 and stays there until i let off the gas. is this a preprogrammed number?
I have the fooling the afc mod on my car to vary fuel delivery based on boost, but i think it is harder to tune using this mod. I have the low set for anything in vac and the high set for anything in boost. but what this does is it doesent take into account throttle position any more. and i think that makes things a little more difficult. i'll mess around a little more and see if i can get it right. thanks James
#28920, "RE: datalogging and LTFT" In response to Reply # 5
>i also noticed that when i floor it my ltft goes to +17 and >stays there until i let off the gas. is this a preprogrammed >number? > >I have the fooling the afc mod on my car to vary fuel >delivery based on boost, but i think it is harder to tune >using this mod. I have the low set for anything in vac and >the high set for anything in boost. but what this does is it >doesent take into account throttle position any more. and i >think that makes things a little more difficult. i'll mess >around a little more and see if i can get it right. >thanks >James
Your ECU will still report fuel trims while WOT.. so.. by the sounds of it you gotta add a bit more fuel to lower the LTFT. Basically your computer has determined that it has to increase the fuel map curve by 17% over it's norm baseline to accomidate your boost.
I haven't had a lot of time to play with the datalogger.. i'm sure there's a bunch of stuff i'm missing.. anyone else wanna chime in on the subject while it's here.
ttyl
WheatKing
-- DSM Junkie -- 4 - 1G talons 4 - Avenger/sebrings 1 - Jeep to tow em home when they break
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