stft and ltft?

[vinh766]

i'm new to logging and i have tried to find info about short term fuel trim and longTFT, i've found info on high trim and low trim, but im not thinking its the same thing. can somebody tell me what i should be aiming for on these two when logging? like at part throttle or at WOT, or if its even important to try to tune.

 

[CanadianTSi]

Ideal Fuel trims would be 0...if there in the + it means your running lean, in the - and your running rich

 

[kpt4321]

Fuel trims are only important to watch when tuning in closed loop, or cruise and idle.

The LTFT is a long term trim stored in the ECU's memory, based on the activity of the STFT over a period of time. The STFT is a trim based on the O2 voltage, which is updated at high frequency to keep the A/F ratio as close to stoich as possible.

Like Canadian said, get them as close to 0 as possible.

 

[vinh766]

thanks

 

[white 2g awd]

Ideal Fuel trims would be 0...if there in the + it means your running lean, in the - and your running rich

so, on my car, my short term is 0, my my long term is -8%, so basically i need to richen my low throttle up more to get the long term at 0?, i've noticed that when i richen it, my short term is not at zero anymore though, so basically get both of them to as close to zero as possible? thanks. didn't mean to thread jack here, just thought maybe we could get a little more into it.

Dustin

 

[kpt4321]

No, you need to lean it out. -8% means the ECU is taking fuel out.

 

[1fast97gsx]

yea richen it just a little bit. It will take some time for the ltft to adjust itself to 0% so don't change it again 2 minutes later if it still doesn't seem right.

 

[kpt4321]

No, he needs to lean it out.

 

[1fast97gsx]

No, he needs to lean it out.

Yea you are right ... I am an idiot. + means richen ... - means lean out.

 

[white 2g awd]

ok, well i actually richened it up on the low today, and its running better, lately i've been having some troubles with backfires on decel, and bad idle, and it just started happening when i leaned out my low throttle, so i richened it up, and now i'm not having the backfire or bad idle anymore, i'll give it a couple days, and see how it does, and see what the ltft is, and if its minus even more, then i'll lean it out again some. kpt4321 i've been trying to follow your tuning guide (i have a copy of it in my car), my safc settings ended up being around -5% on low throttle, even with my 550 injector compensation. i'm still not getting any knock though on low throttle.

Dustin

ps- i have replaced plugs and wires allready too for the bad idle and backfires, i'm going to check the coilpack tomorrow probably.

 

[CanadianTSi]

That backfire on deceleration is probably just unburnt fuel exploding in the Exhaust

 

[white 2g awd]

damn....allright, i'll go beat myself in the head repeatedly...then i'll lean out my car a little today and see how it does.

Dustin

 

[white 2g awd]

hey thanks guys, i turned all my low settings down to -5%, and now my ltft is at -2%, and i messed with the highs some more today, and leaned it out like hell, and now i'm finally getting no knock at 6.5k and up, musta been more rich knock...kinda makes me wonder though, with my mods, my hi settings are -6% starting at 6.2k....but thanks anyways for helping me too.

Dustin