LTFT's

[dayday]

Have not got into the tuning part yet but have scanned several runs on different days. I am seeing LTFT's starting at -10.6 before runs, -7.8 during WOT and -1.6 after runs. Should I be worried about these numbers, and if so, how should I address them?

[2HiPsi]

Well, ideally you want your LTFTs to be at or near zero at all times. A negative LTFT indicates the computer is sensing a rich condition and is pulling that percentage of fuel. When this # is locked in at WOT, if all it knows to do from cruising is to pull fuel, it will do that at WOT.

I try to keep them +/- 3.

As for addressing them, just ordered last night and waiting for it to arrive so I can't help ya there. :P

[Chris@HPTuners]

another thing for you V6 guys to keep in mind is the LTFT's work a little different on V6's. There are only 10 cells (5 for EVAP closed, 5 for EVAP open) and there is no 0 WOT locking if -ve like the V8, they just lock at whatever they were before you went openloop @ WOT (which is usually cell 3).

0 = Idle
1 = Decel
2 = Light Load / Engine Not Running
3 = High Load
4 = Med Load

[Missing2]

HRM.. interesting I am assuming 0-4 is for when evap is open??

Better yet.. could you give us a more complete explanation? sounds like something i need to keep in mind when I get my car tuned.

[Chris@HPTuners]

Yeah,

Looking at the code it works like this (in order of tests):

0 = Idle
- MPH < 1
- TPS < 1.5%
- RPM within 100RPM of desired Idle RPM

3 = High Load
- TPS > 25%
- CylAir > 0.4 g/cyl

1 = Decel
- TPS < 1%
- CylAir < 0.12 g/cyl

4 = Med Load
- Airflow > 24 g/sec

2 = Light Load / Engine Not Running
- none of the above (or engine not running)

Note: all the numbers mentioned above are from the particular cal i'm looking at now, they could be different for other cals.

The fuel trims cells will display 0-4 regardless of whether EVAP is open or closed, would be interested to see examples of > 4 being displayed.

[arthansen]

This needs more explanation. Here is my LFTF table. What is the scale across the top? What do you mean by "10 cells" and the 0 - 4 thing????



You slipped in the above post as I was drafting this. However, the question stands.

[Chris@HPTuners]

the histogram is in VE table format, the scale along the top is MAP/10 (to make it smaller), take a look at your VE table.

if you are logging "Fuel Trim Cell" you'll see that there are 5 cells. compared to the V8 which has 22 cells.

Also, the cell numbers don't really relate to dividing up the VE table into "cells" like the V8's either.

[dayday]

As for addressing them, just ordered last night and waiting for it to arrive so I can't help ya there. :P

Maybe we can start having tuning talks at the monthly meetings.

It's good to see great info coming out of this topic, Keep it coming.

[guardsman01]

Chris, is there any way you guys set it up so that we can make our LTFTs lock at zero if the values are negative, or is that something that would be too complicated to get into?

If you can't, then we need to look into how to tune figuring that in.....

[Chris@HPTuners]

Chris, is there any way you guys set it up so that we can make our LTFTs lock at zero if the values are negative, or is that something that would be too complicated to get into?

If you can't, then we need to look into how to tune figuring that in.....

let me look at it a bit further...

[arthansen]

OK, lets see if I have learned anything. Looking at my LTFT table above, I want to get all those nasty -10 and other very negitive numbers to aound -1 or -2.

To do this, I should adjust the VE table (while watching my WBO2) cell by cell to bring those numbers up.

Then when I go to WOT, it just locks in at the LTFT I was at just before LTFT. As long as they are all around the -1 or -2, that is what I would be at during WOT.

God I hope thats right. If it is close, let me know here. If it is way off, e-mail me ;D. (Just kidding)

[Missing2]

wait.. i am confused..

what is this 0-5 fuel trims about?

just like arthanson i see alot of number both postitive and negative in my LTFT histograms.. that are higher then 5

i am not undertanding something like a retard.. anyone care to explane?

[arthansen]

Nothing greater then 4. Only more negitive then -4. Zero through four are used to indicate load when engin goes into open loop. The goal is to have the negitives all around -2 to -1. That way you are close to zero fuel trim all the time so when you go into open loop, you are close to 0 no matter where you are just before going open loop.

That is how I understand it. Someone that really knows please chim in.

My question is how is the best way to adjust the fuel to adjust the LTFT. Is it the VE table?

[Missing2]

ok.. so the range is like

- something -> +4

ok.. i think i see what you are saying..

[arthansen]

If the LTFT Histogram reports negitive numbers to show where fuel is taken away but the positive numbers indicate the load, how does the Histogram indicate if fuel is added?

I am trying to bring down the LTFTs but what if I go too far? How will it indicate if the PCM is trying to add fuel?

[arthansen]

Does anybody know the answer (see above post)?

[arthansen]

OK, forget what I said. Take a look at this LTFT table.



The Fuel Trim Cell that Chris was refering to was not part of this table. It can be logged (and is part of the default log). The LTFT table is the same as the V8s. It shows Positives where it adds fuel and negitives where it takes away.

The way I got these LTFT was while I was trying to get the LTFT to move by unplugging my MAF. It worked (oh boy did it work). Here is what it looked like before.



I have no idea why it went so far the other direction. I lowered my VE table trying to get the LTFT up but I only went down 5% and only bellow 40 on the VE table. I guess its back to the drawing board.

After what I have seen on the V8 section, I am thinking about going Speed Density. Have any other V6ers tried this?

The reason I was confused is by chance, my car always went to +2 when I went to WOT. I thought this was the +2 Chris ment to mean Heavy Load at WOT. Sorry if I confused anyone.