LTFT learning question
10-23-2005, 08:29 AM
#1
LTFT learning question Just a quick question: The LTFT's are effectively learned by the computer once the STFT's are consistently near zero right? Is this at idle or all RPMs? I've gone about 60 miles and at idle the numbers are good but while driving the STFT's are all over the place. Does this mean it hasn't learned the LTFT's yet?
10-23-2005, 11:04 AM
#2
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LTFT's are an average of STFT's. STFT's will fluctuate constantly in a +/- 2% or so. If they are consistantly averaging a positive number, the LTFT for that driving condition (idling, cruising, etc.) will increase. Same goes if it is consistantly averaging a negative number, the LTFT for that driving condition will go negative. What you want to achieve is LTFT's that don't bounce around too much in any driving condition, while staying just below or at "0."
10-23-2005, 12:28 PM
#3
So once my stft's are oscillating b/w +/- 2% while cruising and idling then the ltft's are learned? Right now they're horrible...ltft's around -11 and stft's around -20. The reason I'm asking is b/c I'm in SD and I just reset the fuel trims about 50 miles ago in preparation for VE tuning.
10-23-2005, 04:24 PM
#4
Ever watch The Price is Right with Bob Barker? There is a game on the show called The Mountain Climber. The man climbs the mountain and the player has to stop him at the correct point on the mountain so he is within a certain RANGE on the mountain for the person to win the prize. Your LTFTs and STFTs are sort of like the Mountain Climber game. Your STFTs are like position within the RANGE where the mountain climber might be located at any given point in time for the prize to be won. The mountain climber can move up and down within the RANGE, but when he hits the upper or lower limit of the RANGE the entire RANGE moves to put the mountain climber back into the CENTER of the RANGE again. The LTFTs move similarly when your STFTs hit the upper or lower limit of their RANGE. STFTs make QUICK, SMALL changes while LTFTs make SLOW, LARGE changes. When you turn the key off you lose your STFTs, but your LTFTs are remembered by your PCM so you have a starting point for you injector pulsewidths.
10-23-2005, 06:45 PM
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And its even more complicated,,, there are 22 fuel cells, each with their own STFT and LTFT values. As you drive down the road going thru gears, the PCM will vary the current active FTC according to MAF flow (or MAP reading) and engine RPM.
The LFTFs are stored at key off and are still available then at key on. The STFTs are erased every time you key off. Therefore, pay most attention to the LTFT values for tuning purposes.
The LFTFs are stored at key off and are still available then at key on. The STFTs are erased every time you key off. Therefore, pay most attention to the LTFT values for tuning purposes.
