Disabling LTFT for good??

[blazenstyle01]

I just started tuning a 1999 camarow ss that has been tuned prior to me. The reason for the re tune is that we just put heads and a cam in the car. I opened the tune and i noticed that the LTFT had been disabled. My question is, what would be the reason for doing this i understand that the LTFT are percentages of STFT and that they are a stored value the the PCM references back to so i guess i could kind of see why you would do this but does it really help you in any way. The one thing that i am seeing is that with the LTFT off my STFT are way out of wack like -15 but when i enable them STFT seam to go down a bit.

[WS6FirebirdTA00]

STFT will go down with LTFT on because the LTFT is going to pull that fuel. STFT should be around zero after enough learn time. Main reason I like LTFT off on my own car (when it was closed loop) is to prevent false + fuel trims at WOT, adding too much fuel.

[Ben Charles]

Is the general consenses to disable LTFT's still? I have NGK wideband for my Blower setup to tune and I think I will disable the LTFT's to dial in the STFT's and never turn the LTFT's back on. Is that acceptable?
Car is a MAF sensor setup if that even matters?

[KLUG'S SS]

Is the general consenses to disable LTFT's still? I have NGK wideband for my Blower setup to tune and I think I will disable the LTFT's to dial in the STFT's and never turn the LTFT's back on. Is that acceptable?
Car is a MAF sensor setup if that even matters?

Should be just fine, alot of people just run STFTs only.

[robbyredneck]

+2 i am currently running only my st's and thinking about going full time open loop.

[5_Liter_Eater]

I have had LTFTs disabled for years now. STFTs only.

[Ben Charles]

Ok guys thanks, seems like there isn't any downsides to keeping it enabled really. Plus from my understanding STFT's learn very quickly and are generally easier to tune than LTFT's anyways??

[5_Liter_Eater]

Thats my take on it. The benefit is positive STFTs do not add to PE like positive LTFTs do.

[copley87blazer]

When you use both stft and ltft toghther dont they take an average and use that???

[Ben Charles]

I am pretty sure that the ECU takes the data from the STFT's and then averages it into LTFT's (my understanding)

Also seems like a MAF-STFT histogram may seem the best way to tune too (Fast and efficient) Anyone want to share theres?

[5_Liter_Eater]

It works like this: STFTs make quick adjustments to fueling. If a fuel trim cell's STFT stays at a certain number for a certain amount of cycles, that becomes the LTFT and the STFT is reset to zero. So LTFT is 0, STFT is +5 for x samples. LTFT becomes +5 and STFT resets to zero. After a while STFT stays at +3 for x samples then LTFT becomes +8 and STFT becomes 0.

[robbyredneck]

and then when you go wot it stays fat or lean. kind of diffusing tuning your open loop for wot and especially boost. thats the importance of getting your lower range ve in check or turning off your ltft's

[69lt1bird]

I will not go lean at WOT because of LTFT, only adds fuel. PE + LTFT additional fuel.

[robbyredneck]

thanks bird, i stand corrected.

[LSxpwrdZ]

I disable LTFT on everything I tune! Most stuff I make run open loop as well cause the customer doesnt want to buy good o2 sensor's @ $50-60 each to make it run correctly. I had bad o2's in my car and did the same and if tuned properly will not suffer any. I still averaged ~26mpg on a trip to Florida with a G5X3 6.0L LQ4 5.3 headed in my 98 TA.

[robbyredneck]

just this week i tested out full time open loop. bye bye o2 sensors. i get lean cruise and lean idle with so far no detriment. ambient temps have gone from 50-90 here in upstate and the car has responded fine.

[Ben Charles]

So from the factory GM uses Closed loop MAF (CLMAF) and disabling the LTFT's permanatly makes is open loop MAF (OLMAF)?

[5_Liter_Eater]

No. Disabling LTFTs leaves only STFTs to do the closed loop function. Disabling LTFT and STFT puts you in open loop.

[smithers]

So from the factory GM uses Closed loop MAF (CLMAF) and disabling the LTFT's permanatly makes is open loop MAF (OLMAF)?

From factory: would be using a VE / MAF blend as well.

[smithers]

No. Disabling LTFTs leaves only STFTs to do the closed loop function. Disabling LTFT and STFT puts you in open loop.

Bill, Running STFTs only (CL) is your recommendation especially for blown applications?
Im going to guess, UNLESS your lower VE (if you were running SD) was dialed in... then the LTFTs would not have much effect on PE.