Ltft's, where should they be at?

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Feb 18, 2003 | 11:23 AM

OC BLACKZ28

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From: orange county, ca

Ltft's, where should they be at?

I have a predator, and it reads the ltft's. I have read that they should be at 0 to -3, but when? Is that at idle in nuetral, or just driving around? At around 1800 rpm just cruising, they are at about -4, but at idle they are at -8.59. Is that o.k? I have a maft, which I have not used yet, slp maf, ported t.b, k&n, lid $ boot with a cat back. Help!!!!

Feb 18, 2003 | 02:50 PM

J&JsTA

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From: Whitby Ont Canada

Re: Ltft's, where should they be at?

<blockquote>quote:<hr />Originally posted by 2000WhiteZ28:

This sounds strange to me, but at idle my Predator shows -8.59 LTFT's most of the time. Another Predator guy said the same -8.59 showed up on his at idle. When I log with autotap at idle I am -1.6 LTFT. You seem to be showing a similar number to the Predator idle number.

How many Predator owners show -8.59 at idle? <hr /></blockquote><img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

Feb 18, 2003 | 05:22 PM

eallanboggs

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From: New Orleans

Re: Ltft's, where should they be at?

You can't expect to make hard and fast rules about LTFTs and STFTs that apply to all vehicles. Every vehicle is different. Generally you should expect the LTFTs to make slow, larger changes to Fuel Trim and STFTs to make quick, small changes. As long as your PCM is able to adjust your tables your OK. When you go too far, either Rich or Lean to an extreme, you should be concerned. Ideally your LTFTs and STFTs would both be ZERO all the time, but that only happpens in the Twilight Zone.

Feb 19, 2003 | 12:56 AM

2000WhiteZ28

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From: Central MD

Re: Ltft's, where should they be at?

By the sound of those numbers, you are fine. The only way to tell for sure is to log with autotap and take an average. At idle you may be -8 and at cruise -4 and when accelerating +4, you average out to about -4. But you may be closer to -2 by those numbers. Predator does not read the LTFT's as often as Autotap does either. The numbers will be a little more understandable with an autotap log.
This sounds strange to me, but at idle my Predator shows -8.59 LTFT's most of the time. Another Predator guy said the same -8.59 showed up on his at idle. When I log with autotap at idle I am -1.6 LTFT. You seem to be showing a similar number to the Predator idle number.

How many Predator owners show -8.59 at idle?

[ February 18, 2003, 12:58 PM: Message edited by: 2000WhiteZ28 ]

Feb 19, 2003 | 09:44 AM

OC BLACKZ28

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From: orange county, ca

Re: Ltft's, where should they be at?

Thanks for your help, I appreciate the info. I tried my maft last night and the #'s went nuts? If I went rich on the maft, the ltft's went further into the negative, as far as -16%. When I went lean just one click, the ltft's went postive? When I put on the ported throttle body, the #'s changed more often from -10 to 0, averaging -4.59. That is w/o the maft. Everything seems to be more rough, seemed that the car was slower. What am I doing wrong?

Feb 19, 2003 | 09:55 AM

jimmyblue

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From: East Central Florida

Re: Ltft's, where should they be at?

I'm confused on the very basics because I
see people saying what appear to be opposite
things about the trims.

Starting with the simplest - positive trim
values means the PCM is adding fuel to the
baseline air meter calculation, to obtain
an average O2 reading it likes. Yes? No?

Long Term means it is going to do this all
the time, for the particular cell of its
operating map that it's currently in, because
this is its learning history. Yes? No?

Short Term means that, right now, it's
adding this much more to immediately close
the O2 loop, after having added the LTFT
to the air meter calculation. Yes? No?

Then there is the question of where your
closed loop LTFT ought to be, such that
when you step off into WOT you will have
the best power mixture. I've seen all kind
of different remarks on this too, everywhere
from negative to positive, some of it sounds
like jiu-jutsu mumbo-jumbo (not to say that
isn't really how it works, but it sure isn't
making sense to the uninitiated).

Is there any well-regarded writeup on the
fuel calculation scheme, where all of this
has been brought clear? I read the LS1 Edit
FAQ pages etc. and it doesn't really go the
way I'm looking for, about this stuff.

Feb 19, 2003 | 11:13 AM

J&JsTA

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From: Whitby Ont Canada

Re: Ltft's, where should they be at?

<blockquote>quote:<hr />Originally posted by OC BLACKZ28:
 Thanks for your help, I appreciate the info. I tried my maft last night and the #'s went nuts? If I went rich on the maft, the ltft's went further into the negative, as far as -16%. When I went lean just one click, the ltft's went postive? When I put on the ported throttle body, the #'s changed more often from -10 to 0, averaging -4.59. That is w/o the maft. Everything seems to be more rough, seemed that the car was slower. What am I doing wrong? <hr /></blockquote>With the MAFT that to me sounds right, LTFT running - so PCM believes it is running slightly rich so it is drawing out fuel. You add more fuel with the MAFT and the PCM draws out more fuel(-16)to compensate. You just have to work with small adjustments and let the PCM learn what you have done and should be fine <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

[ February 19, 2003, 11:15 AM: Message edited by: J&JsTA ]