What will cause LTFT's to jump around?
 

I have a D-1 on a 98' TA and am trying to tune it. When we data log the LTFT's they jump from -17 to +25 during normal driving without changing anything in the computer. The graph looks like a big zig-zag. I tried new O2 sensors but it made no difference. Also, when I put in the new injector size, 42lbs, the car won't hardley run. But if I leave the injector flow table within a few percent of stock it runs pretty good (but not like it should with a blower). I am using Ls1 edit to make the changes. Any ideas?

Re: What will cause LTFT's to jump around?
 

Are you using the stock, screened MAF?

Re: What will cause LTFT's to jump around?
 

It could be a leak either in the intake or the exhaust. At idle it might be sucking in air, causing the LTFT's to look really lean (+25) and under boost it will start blowing air out, causing it to be really rich if you tried to correct for the idle. Are the sensors the same from side to side? That could help you narrow down where the leak is. Intake leak will probably affect both, exhaust leak will only affect the side that is leaking.

That would be my first guess. Good Luck.

-Geoff

Re: What will cause LTFT's to jump around?
 

Yes, the MAF is stock. We even tried a new one, but it made no difference. I'm pretty sure the exhaust isn't leaking but I'll double check. That wouldn't affect the injector flow rate problems though, would it? Also, the MAF is only reading about 4-5 g/sec. at an idle. Is that normal, I thought it was supposed to be about twice that?

Re: What will cause LTFT's to jump around?
 

An exhaust leak would make that side run higher... but the fluctuations you have is what is confusing. I know larger injectors create more fluctuation... compare it to your Inj PW's and see if they correspond. 42's idled great, for me, though.

If it is more of an uuuuup, then dooooown, slow ramping, I don't know. And mine fluctuate more at idle. Cruise is pretty steady. Only at the lower inj pulse widths where it is not very steady are the LTFT's varying a lot.

Re: What will cause LTFT's to jump around?
 

I am seeing similar problems on a 2001 SS with a D1 have you figured it out yet?

Re: What will cause LTFT's to jump around?
 

I can't seem to find any exhaust leaks and I believe the LTFT's were the same on both sides so something else seems to be causing the problem. I have now started looking for a newer car to swap everything over to, since I've heard the 98's had some problems and I'm tired of dealing with it. "01SCSS", just out of curiosity, have you been dealing with Force Fed Performance?

Re: What will cause LTFT's to jump around?
 

So you haven't removed the intake, either?

Re: What will cause LTFT's to jump around?
 

Where is your MAF located? A leak anywhwere between the MAF and the engine might cause that too. Do your LTFT's follow the pattern of high "+" at idle and high "-" at throttle?

-Geoff

Re: What will cause LTFT's to jump around?
 

No, the intake hasn't been off as far as I know. The MAF and all that is factory original. I searched everyware today for any leaks and found nothing. The LTFT's don't seem to follow any pattern that I can tell. If they were high "+" at idle and high "-" at throttle, what would that mean? The computer seems to act as if it has a glitch or something. Sometimes it's pretty fast, and sometimes it's not.

Re: What will cause LTFT's to jump around?
 

Post your issue in the PCM section of the Forum... many of those guys discuss LTFT and PCM issues and may give you more ideas.

Re: What will cause LTFT's to jump around?
 

Hope I can help. What are the cells that you are going lean? My guess is that they are deceleration. If it is only on the decel than you have nothing to worry about. on a decel a temporary lean spot esp when off throttle is no worry either. Have you done the inj offset for 42lbers? You said that both banks were about the same? Reset the fuel trims and give it about 20miles of all kinds of driving. I do not feel that you will get perfect LTFTs but you can get very close. If you have a lean spot thru accell than I would look as others have said for a vaccuum leak are you setting any Lean codes? if not then again no worries. Let me know or PM me.

Jeremy

Re: What will cause LTFT's to jump around?
 

JeremyF, thanks for the help, but I've thrown in the towel. I bought an 01' WS6 yesterday and am going to start the parts swapping this weekend. I've had the blower on the car since May and still don't know what more than about 400 horse feels like. I've had a couple of different shops try getting it to work to no avail. When we put in programs that worked on other identical cars, mine wouldn't even run. I think it's cursed. The funny thing is, when it was stock, I never got beat by another stock one. Thanks again for the help everyone. I'll let you know how the new one turns out.

Re: What will cause LTFT's to jump around?
 

Boostat4500, yes my car is at FFP how did you know? And it's too bad you threw in the towel, although the new one should be cool. Hopefully Keith and Billy will be able to get this one figured out.