LTFT are they really that important!!

[GTO155]

Having positive or negative LTFT does it really matter, once you have achieved your desired A/F.

If i was seeing my desired A/F on my WB logs all the time, does it really matter if the LTFT are - or + ??

GTO155

[GuitsBoy]

Theoretically, that should make your a:f fluctuate. If you had a positive LTFT in the last cell before you went WOT, then the computer will add fuel to your WOT a:f.

[jimmyblue]

They matter to consistency and if you have trims positive
by 10%, they're also 10% range of variation and you are
not going to tune AFR to 1% (more than once in a row).

Larger negatives are not a problem as they will zero at WOT.

LTFTs are the historical accuracy of your setup. If they are
off, it's telling you something. You can get the "right answer"
by various means but having true metering makes the
process of tuning straighter in the end. Changing a param
that is not responsible, is misguided. Like in a relationship
based on lies, you start having to keep track of all of your
previous lies before you say anything else, and sooner or
later one of them is going to trip you up?

Not that I'd know or anything.

[GuitsBoy]

Youve been lying to me jimmyblue?!? And to think I trusted you with my tune! I though that meant something!

[killer01ws6]

I just lost my Drink over that one.....

ROTFL......

[jimmyblue]

Youve been lying to me jimmyblue?!? And to think I trusted you with my tune! I though that meant something!

I never lie to my car. Just da ladies, if they need me to

[GTO155]

Are LTFT in the histograms % added or taken??

If its a +4 LTFT does this mean 4 % of fuel added.

If it is then subtracting say 4-5% from that same cell, in the PE table should do the trick to achieve - LTFT.

Then once they are -, you can continue to scale them as you desire to achieve the A/F you are aiming for.

Am i on the right track here guys, or am i just spinning shit.

??? ;D

[GuitsBoy]

Youre almost on the right track, but backwards.

If your LTFT histogram shows positive numbers, it means the computer had to add fuel to hit stoich (14.7) If you lower your VE table for the corrosponding cell, the computer thinks there is less efficiency at that rpm/map and puts in less fuel. Now the LTFTs will be even more positive because VE commanded less fuel to be mixed cause it was expecting less air.

To adjust correctly (in the right direction anyway): If your trims average positive, add to the VE number of the corresponding cell. I keep tweaking till they all hit -2 or -3 uniformly. Honestly, as long as theyre all under 0, youre good to go.

[QUASAR]

IMO, too much time is spent getting LIFT's in the perfect negative range. Mine are -10, and the car drives fine and trims go to 0 at wot like intended. yea you could spend forever getting it perfect, but whats the point. Get your trims not to go + at wot, adjust PE and spark accordingly and whalla.

[GTO155]

Thats all fine, but will adjusting the PE table also get the LTFT to (-).
Suppose you have a stock standard car and you want to modify the A/F only? Some say you shouldnt touch the IFR coz you havnt replaced the injectors and VE is only if you hav done exhaust, header etc mods.
I dont think PE adjustment only will get LTFT to be (-).

[jimmyblue]

PE "shouldn't" affect trims because the learning is supposed
to only happen when the commanded fuel air multiplier (FAM)
is 1.00 and the O2s can still swing to drive the feedback
process. However, back in the Dark Ages when I used a
Predator I did see PE changes push my trims around.

The airflow values are usually the right way to fix trims,
absent any fuel-side error (like changed injectors or a way-
crusty fuel filter or a lame pump power feed, anything that
takes the mechanical reality away from its PCM model).
If the MAF has not been buggered then it also needs no
fiddling. Most "bolt-on" and even "bolt-in" mods are aimed
at improving the breathing, the volumetric efficiency of the
motor and this model is right at the heart of it all. Like
the MAF is civilization and the speed-density tune is your
monkey ancestors, which one comes out in a bar fight?

[SideStep]

...

If the MAF has not been buggered then it also needs no
fiddling. Most "bolt-on" and even "bolt-in" mods are aimed
at improving the breathing, the volumetric efficiency of the
motor and this model is right at the heart of it all. Like
the MAF is civilization and the speed-density tune is your
monkey ancestors, which one comes out in a bar fight?

WWWHHOOOOO...

I thought the MAF was calibrated at the factory for the factory airbox, and if you change to an after market airbox (lets say Vararam) your MAF is now out of calibration???

???

[GTO155]

jimmy blue, what are the airflow values apart from the VE table?

[jimmyblue]

That's really an airflow bias effect, taking the MAF off its
calibration (more of an issue for the descreened MAF
cars). Supposedly the funky air bridge got engineered
to death and the Z06 MAF table is tweaked up for the
tract as it is. You can see how the bridge would bias the
airflow centrifugally, things that magnify or reduce that
can push the MAF around a little.