LTFT and PE Confusion

[Cringer]

I have heard that the current LTFT correction will be utilized once you transition into PE, positive or negative. And I have also heard LTFT will only carry over if it is positive (meaning you are running lean). Are either one of these statements correct?

I am working on an E38 if that makes a difference.

[dhoagland]

I don't know for a fact, by personal logging.
But from what I'm told by very reliable sources is If you are lean going into PE it will command PE plus your lean error.

If you get your trims in order I really don't think its anything to be concerned with...
(Bluntly if you are so far off with fuel trims entering PE, PE is your least concern).

Do you have a specific issue you are chasing?
RPM and TPS delay in some stock tunes really inhibit PE

[Cringer]

I'm not experiencing any issues, just new to tuning. I see so many professionals and amateurs alike disable them and it's always the same story of "if you're tune is dialed in you don't need them." Well ok...but to me that's not a real answer and IMHO can set you up for trouble later. The only real counter argument I've heard is the prevailing LTFT value carrying into PE...but that seems like an urban legend that keeps getting repeated.

[dhoagland]

I'm not experiencing any issues, just new to tuning. I see so many professionals and amateurs alike disable them and it's always the same story of "if you're tune is dialed in you don't need them." Well ok...but to me that's not a real answer and IMHO can set you up for trouble later. The only real counter argument I've heard is the prevailing LTFT value carrying into PE...but that seems like an urban legend that keeps getting repeated.

Got Ya..

I wish I could give a definitive answer, and now I better understand your question, and agree with your analogy for setting yourself up.
I know there are people here that know that answer.

I'm guessing if you posted the question " Does LTFT error transfer to PE and effect the commanded ratio, Positive or negative"
Then in the body of the post ask "if you disable LTFT, but keep closed loop, will STFT still transfer the same error"?
"Or do fuel trims in closed loop effect PE at all"?

[dhoagland]

I'll keep watching this, and if you start a new thread and don't get any response, PM me and I'll PM the thread to someone who I know can answer

[hjtrbo]

My logs show STFT goes to 0 and LTFT stays rich. Have never seen the LTFT stay lean. If I switch off LTFT I notice a couple of point change leaner on my wideband.

In my experience (E67) yes the negative LTFT carries over and will richen up your PE. I can't say what happens if LTFT is positive as I've never seen it in my own logs.

[dhoagland]

My logs show STFT goes to 0 and LTFT stays rich. Have never seen the LTFT stay lean. If I switch off LTFT I notice a couple of point change leaner on my wideband.

In my experience (E67) yes the negative LTFT carries over and will richen up your PE. I can't say what happens if LTFT is positive as I've never seen it in my own logs.

Did you mean Lean fuel trims will cause PE to richen up a bit?

They way I read your response (which I respect) is negative fuel trims (rich) carry to your PE and increase it a bit (richer)?
That is completely backwards from what I understand.

I've been taught that if you are lean going into PE the computer will command your PE "PLUS" what ever lean value you were running

Thanks for jumping in here!!!!

[GHuggins]

Some early or odd ball gen 3's would carry positive and negative trims into PE. That's where the whole "disabling" ltft's started and probably where the confusion is coming from. On gen 4's only positive long term fuel trims will carry into PE and change PE fueling. Same goes for gen 5's too... Hopefully this will clarify some things. I think hjtrbo just mistyped as the way I read it, it's backwards...

[dhoagland]

Some early or odd ball gen 3's would carry positive and negative trims into PE. That's where the whole "disabling" ltft's started and probably where the confusion is coming from. On gen 4's only positive long term fuel trims will carry into PE and change PE fueling. Same goes for gen 5's too... Hopefully this will clarify some things. I think hjtrbo just mistyped as the way I read it, it's backwards...

Thanks Greg

[GHuggins]

No problem... AND to further clarify in case there's any confusion here for the OP - positive trims are trims adding fuel - long terms of these are what get carried over and used to modify PE fueling. Actually knew a "tuner" back when that didn't know what + or - trims actually did. He just tried to get them close to 0...

[hjtrbo]

Yes sorry gents my bad. Leaner trims adding in fuel.

[07GTS]

then there are the odd ball e38 where some STFT will carry over to PE even with LTFT disabled, i would always get a different PW bank to bank if i was CL STFT only and it reported a couple % on one side STFT before PE, soon as im full OL going into PE was same PW for both banks

[Cringer]

then there are the odd ball e38 where some STFT will carry over to PE even with LTFT disabled, i would always get a different PW bank to bank if i was CL STFT only and it reported a couple % on one side STFT before PE, soon as im full OL going into PE was same PW for both banks

This is a Holden-ized E38 from a MY14 Commodore (but in Chevy SS trim).

I have read you statement a few times, trying to decipher it...I think I understand what you are saying...but wouldn't the PW *always* be the same bank to bank during PE, regardless if one or both short or long terms were disabled?

[07GTS]

im not sure what actually going on but i think most if u use fuel trims it would be a bank to bank error correction, unless its just an odd error in the OS