Another LTFT question

[picnic_george]

Been reading a TON about LTFT. From what I gather you want them close to zero. It would seem to me that anything <0 won't correct @ WOT to a certain extent making it run leaner when it gets hot outside. Maybe I'm backwards here but in any event.

Well let's say LTFT is at 0(or close) tuning @ 70* outside. That means when it's 100* outside there will be correction to make it run the right AFR, but what happens when it's 40* outside? Does the LTFT go negative? Will it correct that way to not run super rich @ WOT?

I guess I don't quite understand still how LTFT really affects the scheme of things. I understand it's based off the o2 sensors and uses that to help correct fueling. But why does it matter if it's +10 or not.

I live in Nevada some people here can relate going from 100ft above sea level to 8000ft above sea level in a matter of an hour. And even more just around town (4500ft) the temp can vary 50* in the same day. It's not surprising to see temps below zero in the winter and over 100 in the summer. Not that I drive my TA when it's 16 degrees outside but I'd like to know what buttons I'm pressing and what the heck I'm accomplishing.

After I do an auto VE and verify my maf is correct, if I reset my LTFT should they be close to 0? Is that good enough? The car is just a play toy for the weekend, but I'd like to go to the race track or just out pouncing around when it's 40 or 100 outside and not have to worry about it being stupid lean or stupid rich over something like this.

Thanks for bearing with me guys, I've read 100 threads involving LTFTs and my eyes are getting crossed.

Kris

BTW the car in question is a 98 m6

[WeathermanShawn]

I know there is probably a LTFT swing per season, but quite frankly I have not noticed it that much. Remember, the airmass (and hence fueling) is determined by the interaction between the VE Table and/or MAF.

In theory, if that airmass calculation is accurate..you will see very little swing in LTFT's as IAT changes. Most of my tune was done in winter..I only see a 1-2 % swing in summer, and most likely it has to do more with the change in seasonal gas blends. Same with elevation..I see very little swing in LTFT's from 5000'-12,000'. But, I also have done a lot of work on MAF calibration and the VE Table.

Only + LTFT's are added to the WOT fueling..Negative LTFT's are zeroed out. So being a little rich never hurts the WOT AFR calculation.

I don't know if this explanation will solve it all in your mind. All I can say is that I see very little swing as IAT and/or elevation changes. If you have LTFT's bouncing around a lot..more tuning is in order.

Thats my O2..:grin:

[picnic_george]

Thanks Shawn. :cheers:

I think I'm going to try your CALC VE deal. Looks almost too simple lol.


I did an auto ve but I think I made a small calculation mistake that's why my LTFTs are off. I was tuning to 14.7 afr when I should have been tuning to 14.2 with the fuel I was using.

Will will the 3% difference in afr(targeting 14.7 when I should have been tuning for 14.2) make my fuel trims go 9-11% +?

Either way I had my car running pretty good on the maf 12.7 WOT and last night running the last of the 100 octane out of it I decided to hop on it in 2nd gear. AFR was somewhere 13.5~14.0 WOT, not real cool with a brand new motor. Kind of stupid IMO since nothing has changed since I drove the car a week and a half ago, it's just been sitting in the garage.

[WeathermanShawn]

I have not yet completely mastered the AFR's of Ethanol. I kept my EQ (1.0) at 14.63 AFR. I am sure I getting some oxygenated additive, but since I tuned everything for 14.63 AFR..it all seems to work.

I like AUTOVE, especially if you know what you are doing. But, for those keeping MAF, closed-loop the CALC.VE method makes a lot of sense..

Try it out and see how it goes. Agree, watch your WOT AFR's..you need to keep those PE MAF Freq. separate from non-PE. Usually the cutoff is ~7000-800 Hz. You'll be able to figure it all out.

All I can advise, is follow the Tutorial to the letter. Make sure your narrowband and wideband are operating normally. You can usually nail it in 1-3 runs..if you follow the program..:cheers:.

Good luck, and keep us advised..

[picnic_george]

Well one obvious mistake I overlooked while doing more reading is that when doing an auto VE on a 98 pcm I'm logging and correcting the backup table NOT the main ve table. While my main ve table and backup ve table aren't even close to matching. I ended correcting the backup ve table to near perfect but who knows how far off my main ve table is.
I think I'll copy my back up ve table into my main ve table and fudge the numbers as close as I can, see if that fixes anythin. When I feel it's close enough I will follow with the calc VE tune which seems to be correcting the main ve table not the backup table.

Please tell me if I am incorrect in this assumption.

No wonder my fuel trims and afr were so far off lol.

[WeathermanShawn]

Yea, I always forget when someone is using a 98 OS, it has the two VE Tables.

As far as what is controlling..I will just say this. If you have MAF-enabled, I have found that the majority of Trims and non-transient airflow (fueling) is primarily controlled by the MAF. In fact, with Trims it is almost a 1:1 ratio. I.E., if your Trims are averaging +10%..usually an overall +10% addition to the MAF airflow values gets your Trims in line.

Of course if you are running pure SD, its all VE Table.

I usually advise people to experiment with each technique. In fact, part of the CALC.VE method (PE Mode) is in fact utilizing AUTOVE methods (open-loop). But, if you end up utilizing the MAF and LTFT's..you can rest assured that with the CALC.VE Table method, your VE Table will be just as accurate as if you used a wideband. Your are simply utilizing the narrowbands in the one range (stoich) that they are very accurate.

Good luck..

[picnic_george]

I want my VE right, I want my maf right, I need my AFR right hahaha. I'll be using a wideband anyways but if the nb02 is what's correcting my ve table so be it lol.

I'm dead set on making it right either way.... Next task is to figure out how to tune an ls2 gto which is an all new engima.