Justin98TransAm

iTrader: (2)

Anyone know why my Long term fuel trims won't go to zero anymore at WOT?
here's my EFI Live log, it's a missfire log so all the cylinder counts are there, but so are the LTFT's thanks.
log

98
Auto
Long Tubes
3400 Stall

tuff

iTrader: (15)

What did you change? Do you have edit

JNorris

iTrader: (4)

Because your LTFT are positive. In order for the LTFT to lock at zero at WOT the LTFT must be at zero or negative while in your other fuel trim cells.

John

Navy David SS

iTrader: (13)

LTFT don't mean squat at WOT - only the O2's. LTFT are used only in lower fuel cells. Like John said, LTFT will hold their value during WOT of what they were in the lower fuel cells.

Easier answer - don't worry about LTFT at WOT.

David

deezel

You can ignore your LTFTs at WOT if you want to...
Most guys try to get the part throttle LTFTs slightly negative to force them to be zero at WOT. The PCM will not pull fuel due to negative fuel trims at WOT. Positive trims at WOT cause random changes in fueling and can be bad, especially if your tuned toward the lean side of things. So if you can get WOT trims=0 then you can use the PE table to tune WOT fueling without the PCM randomly adding fuel based on the weather...

Navy David SS

iTrader: (13)

deezel. So what you are say is that LTFT do effect WOT runs? If the LTFT is possitive than the PCM will add fuel at WOT?

Using LS1 Edit, how would you lower the LTFT? (I just got the damn program. Had someone else tune the car, but I would like to be able to "fine" tune it on a dyno and at the track.)

Thanks for the insight. I have been always told that LTFT have no effect on WOT runs.

David

JNorris

iTrader: (4)

Correct. If the LTFT are positive the PCM will add that amount of fuel at WOT.

You can force your LTFT negative by multiplying the Injector Flow Rate table by a number less than 100.
For instance it your LTFT is +10% then you should multiply the IFR table by 95 and do some test driving to revaluate your LTFT.

FWIW I have never seen any difference in performance with LTFT values between 5% and +5%. If your LTFT are within this range then I would leave them alone.


John

Navy David SS

iTrader: (13)

So, by lowering/raising the IFR you directly effect/change the LTFT?

David

Justin98TransAm

iTrader: (2)

cool. I need to do some editing. I'm trying to get all my bugs worked out before I re-install the supercharger

mikey

iTrader: (6)

You will need to modify the main VE table to get all the cells to similar negative values. JNorris is correct, the PCM will add fuel to WOT if the LTFT values are positive.

Navy David SS

iTrader: (13)

Mikey, JNorris said to do the IRF tables, you say the "main" VE table. Which one - or both?

Say if the LTFT is +10. Would you say to do a 95% across the board in both tables. Do a test run. Re-look at the LTFT and than leave or adjust accordingly? (I am assuming that if the LTFT is -10 you would do a 105%?)

Thanks. Maybe this old man can learn something. I just hate hi-jacking Justin's trend. I do have some other questions on "track tuning" in another trend. Maybe you guys can help out

David

JNorris

iTrader: (4)

Navy David SS,

VE tuning really depends on your mods. If you are stock internal then you probably do need to mess with the VE table.

Your assumption (assuming that if the LTFT is -10 you would do a 105%) is correct.

After you make a change in the IFR table you will need to drive around a bit so the PCM will have time to react to the changes. Vary your driving so that the car operates in as many of the Fuel Trim Cells (FTC) as possible.


John

deezel

I agree with JNorris. Use the IFR table first to get your fuel trims where you want them. I have my IFR table scaled to 93% of its stock value.

VE tuning is a lot trickier. Changes to the VE table have different effects at part throttle versus WOT. VE tuning works well for smoothing out part throttle stumbles. I am still trying to figure out how VE changes affect WOT fueling... its definitely not a 1 to 1 effect.

GrannySShifting

iTrader: (10)

even small percentage ltrims stuck at wot can throw power off a little bit. Generally doesnt seem to harm them when they are even, but sometimes one will zero out, and the otehr will add 5%, most times engine makes less power than if both banks were getting a consistant o or 5% ltrim added onto it. uneven burn cylinder/cylinder loses power too.