GMCVT

iTrader: (1)

After installing the below mentioned parts and going through procedure to tune the VE table, I made my first round of adjustments. Originally, my LTFT's were in the -12 to -14 area and STFT weren't to far off. After the adjustments were made I gave it about of hours worth of drive time and my STFT have come way down but my LTFT's are still predominantly at the same spot they were. Am I doing something wrong? I posted several times and then ended up deleting my post because I'm afraid the answer is out there in a search and I just missed it, and I didn't want to create an unnecessary post but I cant seem to find this scenario so could you guys just take me to school here Kinda new at this tuning thing.

Silverhawk_02TA

When you say your STFT's came way down, do you mean that they are going negative, or just that they are close to zero? Because if they are going negative you are adjusting your VE table in the wrong direction.

Another question: Are you resetting your LTFT's after you tweak the VE table?

GMCVT

iTrader: (1)

Yeah, sorry about that. I should have made that a little clearer They have moved closer to 0 and in some cell's they have gone +. Also I did re-set the trims after I changed the VE table.
Let me throw another ? at ya, in the scanner utility it ask for "fuel trim learn" OFF or ON, what is the purpose of this function. I would have thought that the PCM would automatically do that. Thank you for your help!

luv2spd

iTrader: (1)

Fuel trim learn is always going to be on unless you turn off ltfts in the editor or use the vcm controls on the scanner.

Silverhawk_02TA

It just lets you temporarily disable LTFT's. Also if you have disabled them in the editor, it allows you to temporarily enable them.

And another question for you: you are running in SD mode, are you not?

Edit: At this point, I'm going to assume you are, because I think I see what's happening. From your first post you say the your LTFT's were -12 to -14, and that your STFT's "were not too far off", by which I assume you mean they were around -12 to -14 as well. So, if for a particular cell your LTFT is -12, and your STFT is -12, this equals a net fuel correction of -24. So, if you simply copy your LTFT histogram and "paste special - add" to the VE table in the editor, you are only making half the correction. So, your LTFT's will learn out to be about the same, but you STFT's will be closer to zero.

Tuning with LTFT's alone is not really utilizing all the info. To do it properly, you need to add both the LTFT and STFT value for a particular cell before applying it to the VE table. Otherwise you're taking the long way around. Then, once your LTFT's are within +/- 10, you can disable them and just tune with your STFT's.

GMCVT

iTrader: (1)

Yes, I set the mass failure to 0.

Silverhawk_02TA

I edited my post above.

GMCVT

iTrader: (1)

Well, I actually used the method that your speaking of except that instead of adding the 2 #'s together and entering that as the value, I added them up and then divided them in half as per the directions at the bottom of the tuning 101 section. Actually, I had a post about this very thing because I was a little confused about it. At the beginning of the 101 it says to simply use LTFT's values then twords the end it says to add the LTFT and STFT and /2. So I used the latter of the two. Now that you have brought this up, as you pointed out, I still ultimately ended up not correcting enough. Now in the cells where the LTFT is -12 and the STFT is say 8, then the correction factor would then be -4 correct? I still dont quite understand how the STFT can be showing a + amount and the LTFT can show a strong - amount. I'm not very smart

Silverhawk_02TA

Yeah, when your trims are off by that much, you're better off just using the full value IMO. You may overshoot a little, but you'll get to where you want to be much quicker. Once you start getting close to zero and tuning with your STFT's, it's a good idea to start using half the value, since you will be making much smaller changes.

Since STFT's are a moment to moment reaction to what the O2's are reading, they vary wildly over time. In your STFT histogram, first display min value, and then max value, and you'll see what I mean. This is why we use the "average" option on the histogram. Under closed loop operation, the PCM is not maintaining a steady AFR. It is constantly cycling between rich and lean. This is why the charted O2 voltage looks like a sine wave. First, the O2's will read a rich condition, so the STFT's will go negative to lean the AFR down some. Then the O2's will read a lean condition, so the STFT's will go positive to compensate. If you ever hook up an AFR gauge, you'll be able to see this in action as the LED's bounce around from rich to lean.

This being so, if you only fall into a particular STFT cell for a brief period while you are logging, you could see almost any value, and it could have little correlation to what the true (average) STFT really is. The only way to get an accurate STFT is to hit the same cell again and again and again on the same run. This is where driving method while you are logging plays a huge role. Driving "normally" you will hit some cells quite often, and others very infrequently.

Now, this is the part where I leave you hanging...

Seriously though, I've seen several questions about tuning with STFT's in particular lately, so I guess I'll throw together an "STFT tuning guide" or some crap like that which outlines the method I used, which worked very well for me. Maybe I'll include it in a larger "Tuning Guide" to throw into the pile with all the others. It'll give me something to do with my time now that I'm unemployed.

So, keep your eyes on this forum. I'll throw something up here soon.

GMCVT

iTrader: (1)

Man, you have gone above and beyond! That clears alot of that up. Thank you so much and I will keep my eyes open

GMCVT

iTrader: (1)

Well, I did as you suggested then cleared the trims and went out for another drive. Not long enough by no stretch only about 10 min.(had to get back home to my little girl) but some trims had already risen to -9 to -10. To that end, they definately came down but some of the cells have probably had 24 to 30 percentage points removed on the VE table and some of those same cells are still showing -9 to -10. Is it common to have to pull this much from the VE table? Again, so far the overall table is -4 to -8 but as I said earlier, I havn't driven it alot yet. I've noticed my idle is now wanting to die again but it does seem to accelerate better. Does this sound right? Thank you!!

Silverhawk_02TA

My advice at the moment would be to be patient. When your LTFT's learn themselves out, they very well may go more positive. More than once I've logged after a day or two of normal driving after tweaking my VE table and seen LTFT's in the negatives, only to log again after another day or two and have them all positive. This is what takes tuning with LTFT's such a bitch. Give it a good solid hour of driving, while actively trying to hit various RPM and load states. Also, when your STFT's are all close to 0, that's a good indication that your LTFT's are learned.

Don't know about the idle.

If you want, you can send your .bin and log file to bluetorp@yahoo.com and I'll take a look.

GMCVT

iTrader: (1)

Email sent, thank you!!