STFT and LTFT.... What do they mean?

[H3br3w_Ham3r]

Just as the title states. What are these values I can view on the dashawk? And what do they mean?

 

[bigdaddy]

Im pretty sure its Short Term Fuel Trims, and Long Term Fuel Trims. Ill be honest, I have no idea what they mean...lol.

 

[Silver Ecstasy]

Oo..i'm gonna say it nicely before someone else says its: search.

LTFT's show adjustments being done to your fueling. + means it's adding fuel, and - means it's pulling fuel. + or - 10 is within normal parameters, anything higher means you have a boost leak or pulling unmetered air. Something that you should address immediately.

 

[RC08MS3]

clicky

You might or might not understand the link, but STFT is a real time read of how much the computer is adding in fuel to reach the mixture you want, and LTFT is what the computer has learned SHOULD be added to get the mixture you want.

When i say mixture i mean AFR

 

[RC08MS3]

Oo..i'm gonna say it nicely before someone else says its: search.

LTFT's show adjustments being done to your fueling. + means it's adding fuel, and - means it's pulling fuel. + or - 10 is within normal parameters, anything higher means you have a boost leak or pulling unmetered air. Something that you should address immediately.

you mean STFT shows adjustment being done to the LTFT.

 

[bykeryder4life]

ltft is saved data that the ecu has gathered so when your car is running its got a starting point of how much fuel it needs to add or subtract in that maf voltage to hit target afr. stft is the instantaneous adjustments that the ecu is making to reach target afr's if they are slightly off from target/where the ltft puts it. ltft just makes it easier and faster for your car to trim the fuel amounts on the fly via the stft

 

[bykeryder4life]

stft aside, if you have a negative ltft the car is seeing too much fuel or not enough air so its trimming out fuel to lean out the afr. If your fuel trim is positive the car is seeing too much air getting into the system(vac/boost leak post maf) so its adding fuel to account for that so afr richens back up to target again.

 

[Mid_Life_Crisis]

In a properly functioning system, the LTFT should change over time as the engine learns, and the STFT number become smaller as a result because the LTFT figures are closer to being perfect for the car. If your MAF is not calibrated correctly, this may never happen. This is why the first thing you should do if you get an AP is calibrate the MAF.

 

[ReNaToMS3]

In a properly functioning system, the LTFT should change over time as the engine learns, and the STFT number become smaller as a result because the LTFT figures are closer to being perfect for the car. If your MAF is not calibrated correctly, this may never happen. This is why the first thing you should do if you get an AP is calibrate the MAF.

Mine keeps changing ALL the time because i got an intake/TIP and no tune. It's around 11% driving, 19% idle. I checked the installations 3x and don't see/hear a leak. Changed the purge valve, same thing. Maybe the intake is just pulling so much (cold, 40 weather) air?

So i bought an AP and going for a protune this Saturday. Best thing i'll probably do.

 

[mrdouble99]

In a properly functioning system, the LTFT should change over time as the engine learns, and the STFT number become smaller as a result because the LTFT figures are closer to being perfect for the car. If your MAF is not calibrated correctly, this may never happen. This is why the first thing you should do if you get an AP is calibrate the MAF.

How easy it is to calibrate the MAF with the AP ?

And let's say i'm putting the stock map to go to the dealer.

Is the calibration i made with the AP will be a problem when i put the stock map or the stock map will put the calibration of the MAF like it was before i use the AP.

And when i put the AP map back after do i have to recalibrate the MAF again ?

TY for your answer

 

[H3br3w_Ham3r]

This is why the first thing you should do if you get an AP is calibrate the MAF.

How do you do this? I have an AP and a ATR and am going in for a tune next Wednesday.

 

[Sacrilicious]

Mine keeps changing ALL the time because i got an intake/TIP and no tune. It's around 11% driving, 19% idle. I checked the installations 3x and don't see/hear a leak. Changed the purge valve, same thing. Maybe the intake is just pulling so much (cold, 40 weather) air?

So i bought an AP and going for a protune this Saturday. Best thing i'll probably do.

what you're seeing is not that your LTFTs are changing "all the time". there are actually different LTFTs for different ranges of MAF air flow. the ranges correspond roughly to:

idle
light throttle
moderate throttle
heavy throttle

some of them may turn out to be the same depending variances in people's cars, but the ECU switches to these distinctly different values as it senses more air coming in through the MAF. now, within these ranges, the ECU will adjust said LTFT based on what it "learns" it should do by looking at the STFTs, but once it reaches the next range, it will drop the previous LTFT and start using/learning with the LTFT for that particular range.

now, whether you have anything to worry about depends entirely on your car and what parts you have on it...what intake/inlet are you using?