LTFT adjustment

[eboggs_jkvl]

Do you guys realize how much a person can get confused in here with a search on LTFT adjustment?

Ok, no wide band right now so I know I'm a sinner yes, I'll do penance in the morning but...

Trying to do this crap correctly. I loaded a stock MAF setup into the car (I've been using the MAF to adjust LTFTs and from what I see, that's a mortal sin... sigh...)

Ok, I drive and I average my LTFTs and get +8.0

Without doing SD or the other mumbo jumbo, can I simply highlight the VE (both) table and multiply by -10%? Will this pull the LTFTs down to the negative (or start to the negative) range.

Elmer

[eboggs_jkvl]

Yes or No.

[dfe1]

Yes or No. Frankly, it's anybody's guess. I haven't ever seen a 1:1 correlation between fuel trim percentages and VE numbers. I've modified the VE table in areas where the trims were 6-7% on numerous occasions and VE changes of 3-4% were sometimes not enough and sometmes too much. I think this is actually normal because if you look at you data logs closely, you'll find different trim values for the same cells at different points in the log. The same is true of BEN data. Look at a cell in a BEN map and you'll see a significant difference between maximum and minimum values-- and that's in speed density, open loop mode.
I don't think you'll ever see dead consistency unless you can control ALL the variables, which is virtually impossible outside of a test lab. For what it's worth, I've had the best results by making small changes, testing and making further small changes until I achieve the desired results. And don't worry about tuning with the narrow band sensors. As long as you're working with 14.63 AFRs the narrow band sensors will get you really close.

[eboggs_jkvl]

Well, that was certainly a long "yes or no" :)

Ok, we'll give it a whirl and use the same logic -% to go leaner +% to go richer.

Thanks for the reply.

Elmer

[johnsZ06]

I've found the same thing as dfe1 and basically approach tuning the same way. I make adjustement small increments at a time until my VE table is close to where I want it. Then I attack other areas such as timing etc. to see if I can improve upon anything.

[Joel_SS]

Well, that was certainly a long "yes or no" :)

Ok, we'll give it a whirl and use the same logic -% to go leaner +% to go richer.

Thanks for the reply.

Elmer


FWIW. My LTFT were in the +20 range on average. I added 10% to my main ve table across the baord and got my LTFT down to about +11 on average. But from what I unerstand +11 is still way to high..

[BACKinBLACK]

if i remember correctly you actually want your ltft's to be around -12.

[dfe1]

Actually, LTFTs should be in the 0 to -4% range. Try working the areas that are the furthest off by adjusting 4-5% at a time. Once you make the corrections indicated by the scan logs, go back and blend in the adjacent cells. The overall map should be relatively smooth. If it looks like the Rocky Mountains, you have more work to do. Keep in mind that the values in each cell have a relationship with the values in adjacent cells.

[Joel_SS]

Good info, but I think my LTFT are off becasue I have an intake leak.

[BACKinBLACK]

well you are having better luck then i am. My ltft's were at least 14 and
15+% so i added 30% to the entire VE table and it really didnt help at all. It appears to have helped in some ranges and other ranges the LTFT's went even higher. So what do you guys recommend in this situation. I can send some one the copies of my logs and my tune if some one would look at them for me. i would post a link but i have no idea how to host it.

I would really appreciate some help here, this is really frustrating me and im about ready to park the car for long term bc of this. Also this seems to have been a problem since i changed my ypipe but the only leak i can find is about 3 feet down past the collectors and the O2 sensors so i didnt think it would affect it that much. Also i cant get it to idle worth a crap either anymore. I have logged and changes my RAFIG according but each time i add the amount it shows i need, the next time i log it, it goes up more so i keep adding. Im in the 33 range now at 20C.

Thanks for any help you guys can give, its really frustrating me

I have a 00 SS
F14 cam (232,234 .598,.598)
Fast 90 NW 90
Mac mids, ORY
and a bunch other supporting mods.

[redhardsupra]

if you're adding to the VE table and there's no change in resulting fuel trim scans, then you haven't truly disabled MAF...ask me how i know :/

[BACKinBLACK]

well i havent tried to disable the maf that im aware of. I havent auto VE'd it, and im not trying to run in SD or anything im just trying to get my dang car to run. After i added 30% it wouldnt hardly start or run at all. So it seems to me that its already getting to much fuel but for some reason the O2's are still reading lean and making the LTFT's add more fuel. Wouldnt that seem correct to theorize?

[redhardsupra]

go sd and start scanning. worked for everyone else, will work for you. don't reinvent the wheel.

[Bruce Melton]

go sd and start scanning. worked for everyone else, will work for you. don't reinvent the wheel.

So tune VE in SD even if you are going back to MAF?

[SSpdDmon]

So tune VE in SD even if you are going back to MAF?
Yup. Get it close with the VE knowing it will never be perfect. Then, tweak your tune by dialing in your MAF.

[BACKinBLACK]

so are you saying that my Maf is off? It is the stock maf with stock table , but i know its still possible. I just figured that eventualy the LTFTs would catch up

[redhardsupra]

the process of calibration of MAF is based on first mapping out the volumetric efficiency table as close to perfection as you can, and then mapping it onto the maf table. the reason why we tune ve in sd is that most of the time in normal operation we don't go purely off maf or purely of ve, but off the mix. so by ignoring maf's inputs, we can tune the ve (because it's the only source of info, thus it's easy to make corrections estimatimated by fuel trims). then the trick is to match the frequencies of the maf with the airflow calculated through the ve table, and then 'tell' the maf which frequency signifies which airflow.
it's all been beaten to death, read the 'how does maf really work' in the stickies on ls1tech, it's a mighty good read if you want to achieve a deeper understanding of the topic.

[joecar]

Eliminate all the variables but one (VE table), dial it in, then add one variable back and dial it in (MAF table) using the known-so-far variable(s), ...

[BACKinBLACK]

cool. ill put that in the info vault up top. ive been reading so much my brain went into melt down

[Joel_SS]

Ok guys really dumb question. Can I do the AutoVE tune with oua WB 02? I have read the step by step and see it calls for one but was just wondering.. Sorry I am a big time rookie!

[SSpdDmon]

Nope. You can use the stock narrowbands (STFT's + LTFT's) to tune cells that normally command a 14.63AFR. But, that usually needs a spreadsheet to make things easier. I put something together in Excel that made it fairly easy.

[ringram]

Well you can make a calc pid that sums the trims and turns it into a ben factor. something like (((stft1+stft2+ltft1+ltft2)/2)/100)+1
Use that pid in a map with MAP vs RPM matching your VE table and just like magic you have a NB02 autotune method.

One good thing, if anything good can be said about using nb02's is that you get feedback from both banks.