question about ltft.

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Dec 18, 2004 | 02:03 PM

Tiger2o69

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From: MS

question about ltft.

I ran a few runs and my ltft were between 5-9 so I posted asking about how bad that was and was told I needed to get to negative b4 running nitrous. I know how to fix them now I believe but i was just wondering if its normal for them to be off like that with my mods or should I be looking for a cause?

thanks for the help

Dec 18, 2004 | 02:09 PM

horist

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From: Lake Zurich, IL

when you do any mods that allow for more air to enter the engine, the VE table becomes scewed ... before it was setup for stock... it expected at a certain MAP and RPM that xx% of the air entering is useable for combustion (or rather xx% of the max amount that can fit into a cylinder under non boost applications)

Now you allow more air to enter, so the PCM has to add fuel (positive LTRIMS) to compensate for a lean condition ... you shoulda seen my LTFT histogram after my 382 upgrade... it was really whacky

Dec 18, 2004 | 07:24 PM

Tiger2o69

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From: MS

ok, that was what i was thinking but was making sure. I started tuning like the helf file shows for the ve table but it was still a good bit of red so I did it again and again lol and then smooth it over. I hope im not hurting anything. But I suppose if im not going negative in the histogram im ok right?

I did not unplug my maf tho. Do you think it is better to run w/o it? Also I have seen that ported maf ends are bad but if I fix the ve table would it be ok?

Lean?? I was under the impression I was running rich. On the histogram during wot my numbers are saying 900+ isnt that rich?

Last edited by Tiger2o69; Dec 18, 2004 at 07:31 PM.

Dec 18, 2004 | 08:06 PM

horist

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From: Lake Zurich, IL

Quote:

Originally Posted by Tiger2o69

Lean?? I was under the impression I was running rich. On the histogram during wot my numbers are saying 900+ isnt that rich?

+ Ltrims mean the PCM is adding fuel ...

Are you locking in at + Ltrims at WOT?

part throttle.. the PCM will constantly correct itself... ideally you want 0 for all cells MAP vs RPM ... this means that you're at 14.7:1 all across the board (or close to)

at WOT the PCM goes off of the VE table and the PE values... .900 at WOT is nice... what are your LTRIMs at WOT? If they lock to 0 then you're gold

Dec 18, 2004 | 09:13 PM

Tiger2o69

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From: MS

Most of the time its locking in at 0 but somtimes its locking in at 1.

After the last time I added about 5 to all the cells and reset the fuel trims the histogram was showing -10's and -11's. Then after about 10 mins they went to mostly 1's and 2's and some 3's 4's and 5's.

Do they need to be 0 or negative during normal driving or is it -4 to +4 is ok? In the help file is said this was good but I was told everything needs to be 0 or negative.

Dec 18, 2004 | 09:16 PM

horist

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From: Lake Zurich, IL

from the info I've been told, +/- 4 normal is acceptable... main thing is you want LTFT to lock in at 0 at WOT , so that your PE table is accurate

Dec 19, 2004 | 05:44 PM

Tiger2o69

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From: MS

Ok I did a lot of messing with the ve table and it looks like I have done too much adding but it still doesnt look good. I looked a lot of tunes from your site and none seem to be as high as mine

Here is my latest attempt at getting things negative. Looks like alot are negative but some are still positive. My car is acting funny now tho so im about to back off some of the fuel.

here is the ve table

here is the graph

here is the stft

here is the ltft

Last edited by Tiger2o69; Dec 19, 2004 at 06:02 PM.

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Dec 20, 2004 | 01:12 PM

Tiger2o69

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From: MS

after trying and trying to get things negative I decided in the above to get things negative and work my way back to 0. Looks like it put some things negative but w/ a lot of the cells being 100+ and as I stated above I havent seen anyone's table that high after looking at a lot other people tune. The car was kinda sluggish and during constant driving i felt it kinda jump every once in a while.

After reading a lot of stuff I found that I may need to multiply my maf table by 105% to correct the removal of the screen. That is what I just did and im about to go log that now.

If that doesnt work I read a post from a few months back where someone said they pcv mod was causing a vacuum leak and he couldnt get his ltft to go to 0 which is the problem I am having so i will remove that and do some logging.

Once you see the post let me know what you think about the above graphs, am i right that i added to much fuel and there seems to be another problem. also is there anything else you could think of causing the problem? And what can i do to check?

thanks for the help