SD Tune LTFT Issue

[aaronc7]

I haven't touched my tune in quite awhile, so I'm a little rusty on my LS1 knowledge. But I changed injectors, so I'm back into it now for a bit.

I'm having some weird LTFT issues/observations when running the car in SD mode, and curious if anyone help point me to WHY, it would be greatly appreciated. It's not a huge issue, I'm mostly bothered because I can't understand what's going on exactly.

P59 flex fuel (-7603 OS), 2003 Corvette Z06. Mild cam, LT headers, pretty standard setup. LS3 MAF.

The car was running a 'normal' tune with MAF enabled etc. Ran the car with MAF enabled' +10 LTFT or so in idle regions, but that was about it, no issues really.

Flashed to SD COS, failed the MAF in order to run speed density. To both tune the VE table and compare how it ran/see if I wanted to run SD mode.

When running SD COS/MAF failed, it needed around 15-20 percent fuel pulled at idle. The weird issue: LTFT pegs at -8.6% and will never exceed that. So for example, LTFT will hit -8.6 and STFT will continue to pull around 6-8* fuel or whatever. When I shut down the car, LTFT resets to -1.6% every time, for every fuel trim cell (that were all 'maxed' at -8.6% on previous drive).

Is this a SD mode thing that I'm totally misremembering, that LTFTs don't quite work right? I don't think this can be right, but driving myself nuts trying to figure out what's going on.

I haven't touched the LTFT min/max limits, which are set to 0.8 and 1.25 IIRC. Which should mean -20 to +25 LTFT range.

I can post a tune/log later when I'm back on the PC, but the only changes between my 'MAF' and 'SD' tunes are failing the MAF and I zero'd out the MAF table (which probably isn't necessary, but I don't think that would be related either)

[GrannySShifting]

Ive seen this before, and I think it has to do with what fuel trim cell number its in (cell 14 18 whatever)

I never leave LTFTs on anymore anyway, Id just disable them and dial in the STFTs very well and call it a day

[aaronc7]

Ive seen this before, and I think it has to do with what fuel trim cell number its in (cell 14 18 whatever)

I never leave LTFTs on anymore anyway, Id just disable them and dial in the STFTs very well and call it a day

I didn't want to make my post too long and verbose, but weirdly enough, FTC 20 (idle, evap closed) that you get for ~100s after starting up. The LTFT didn't seem to be limited-- it would go to -15% or whatever. It's the "normal" FTC that seem to be "limited". In this case 18 and 19 for Idle, AC on/off.

But either way. After turning the car off, FTC 20 (and the others), ALL reset to -1.6% exactly.

Turning off LTFT was my next move, but unfortunately I'm the kind of guy that liked to figure stuff out and it bugs me to no end when I don't understand what's going on.... it's a flaw of mine lol.

It just struck me as weird that in MAF/normal mode, it's fine, and very very minimal file changes. It's like it's in some sort of error state. I get the MAF failed DTC as expected, but that's it.

Thanks for the reply/thoughts.

[GrannySShifting]

I didn't want to make my post too long and verbose, but weirdly enough, FTC 20 (idle, evap closed) that you get for ~100s after starting up. The LTFT didn't seem to be limited-- it would go to -15% or whatever. It's the "normal" FTC that seem to be "limited". In this case 18 and 19 for Idle, AC on/off.

But either way. After turning the car off, FTC 20 (and the others), ALL reset to -1.6% exactly.

Turning off LTFT was my next move, but unfortunately I'm the kind of guy that liked to figure stuff out and it bugs me to no end when I don't understand what's going on.... it's a flaw of mine lol.

It just struck me as weird that in MAF/normal mode, it's fine, and very very minimal file changes. It's like it's in some sort of error state. I get the MAF failed DTC as expected, but that's it.

Thanks for the reply/thoughts.

Ive seen the reset to -1.6% vs 0% too many times, and just regard it as a reporting error in HPTuners like many other things these days Theres certainly some stuff they have wrong in many departments reporting, buttons not working as they should, OS missing stuff or labled funky but they dont care it seems because for the most part people are done spending money on those OS

[eXo3901]

But I changed injectors,

?and input the correct injector data?

[aaronc7]

Ive seen the reset to -1.6% vs 0% too many times, and just regard it as a reporting error in HPTuners like many other things these days Theres certainly some stuff they have wrong in many departments reporting, buttons not working as they should, OS missing stuff or labled funky but they dont care it seems because for the most part people are done spending money on those OS

Funny, my first thought was something like, "man I bet this COS software is buggy or something".... so I flashed the same/similar file with EFILive on their COS and I had the exact same issue. So more than likely it has to be something in the calibration or stock logic, I think.

[aaronc7]

?and input the correct injector data?

Yes, of course. I've changed injectors like 4 times now lol. I just know that even with good data, you're probably going to want to tweak the VE/MAF tables, so that's why I'm back at it. Overall the car drives fine, drove it to work a few times now.

[aaronc7]

Well, I don't have a big update or really any sort of resolution, but I did a bunch of testing yesterday evening and figured I would report back.

I tried about 10 different file revisions, one changed at a time. Mostly goofy stuff that shouldn't matter, but I was really grasping at the straws. This is back on stock 12587603 OS just to eliminate one more variable.

In all cases, LTFT was goofy in SD mode. The 'normal' VE table FTC were limited to around -9 or so and would reset to exact -1.6 when the car was powered off. One time I played around with the diag tools in VCM scanner, and messing around with the evap/purge/vent to ON and OFF and it allowed the LTFT to exceed this random -9 limit, but wasn't able to reproduce it.

Thinking back to my prior LS1 tuning SD experience.... it was all on the original P01 PCM, so this is the first time I have played around with P59 SD. The only reasonable conclusion I can come to is they behave a little differently in SD mode, and in my view P59 acts a bit more odd.

I will probably just disable LTFT and move on, or turn the MAF back on and proceed that way.

Weird issue, still don't really understand it. But moving on for now