Results 1 to 8 of 8

Thread: +20 LTFT at idle

  1. #1
    Banned
    Join Date
    Nov 2008
    Posts
    69

    +20 LTFT at idle

    This is for a 98 Montana Transport. The tune was done by another tuning software, not HP Tuners (the other one mostly used by GM 3800 V6). I tried to fine tune the VE and MAF. According to the scan, everything is acceptable while driving. However, when the TPS reach 0%, LTFT jump up to around +20. This happen when idle or, when let off the gas while driving, ie braking. Once the throttle body open, the LTFT will return to normal.

    There's not much available data from the scan, only basic stuff (still waiting HPT support team to map out my PCM file). I used Excel to sort out the MAF (kpa), RPM and LTFT to do the adjustment in VE table.

    I attached the scan log, VE, MAF and Timing table. The MAF is almost stock. The VE and timing are the ones I played most the time. I know there's not too much info and I appreciate any suggestion.

  2. #2
    Advanced Tuner BigDaddyCool's Avatar
    Join Date
    May 2009
    Location
    Brisbane, Queensland
    Posts
    767
    While I am just a junior tuner (been tuning bout 6 months) ........ it would seem that most of your run is running lean........... It's hard to tell really, either it's it's tuned really well as to why it shows up at 0.00 at times on throttle......... or your in PE mode like virtually above 40% throttle.

    Can be a couple of things, depending on your cars setup tune wise........ your commanding too much air for the torque your making? the curves coming off the throttle are out....... you need to richen it up a little so when u take ur foot off it doesn't lean out so bad.

    Can be to do with fiddling with VE. You'd need to post ur tune file. Both stock and what you've modified.

    PS. I would say to elivate the problem, richen up your tune slightly so it's in -2-4's all the time. I find it's better for cars to be pulling fuel then trying to add it. It could also be a actual problem like a vaccum hose. Idle bypass valve etc
    Last edited by BigDaddyCool; 08-24-2009 at 03:11 AM.

  3. #3
    Advanced Tuner HawkZ28's Avatar
    Join Date
    Feb 2009
    Location
    Waverly, NE
    Posts
    475
    You are running really lean the majority of the time. Set up a histo that maps the LTFT vs MAF Freq, and tweak your MAF. Then, go after the VE, if at all. Mine only runs a bit lean when IAT's are 130+. Otherwise, I'd say as high as it gets is 1.6, but averages 0 to -1.6. When I first started tungin our 3.4, my LTFT were running -8 to -12 under accel. The way I understand it, VE is used for transitional fueling, where as the MAF is the majority of the time.
    Hawk

  4. #4
    Banned
    Join Date
    Nov 2008
    Posts
    69
    I'm still waiting for the support team to map out my file. I'm tuning it with another GM V6 tuner. That's the reason why I can't even setup a histogram. Most of the time it run lean is throttle close. Whenever the throttle open (regardless what TPS%), the LTFT goes back to normal.

    I start out with VE first. I turned off the MAF and PE. I can get it close to +/-3, however, once I turn back on the MAF and PE. It jump back to +20 when throttle is close. My PE will enable at 30% TPS at all RPM range. Also my PE base A/F is 13:1. Do you guys think that's my problem?

  5. #5
    Advanced Tuner HawkZ28's Avatar
    Join Date
    Feb 2009
    Location
    Waverly, NE
    Posts
    475
    I could be wrong here, but if you disable the MAF, and it idles fine, and after you re-enable, it goes lean, the problem is with the MAF calibration.

    I 2nd checking for a vac leak somewhere, too. On our 3400, there are a lot of vac lines that had weak at best connections at 100k.
    Hawk

  6. #6
    Banned
    Join Date
    Nov 2008
    Posts
    69
    Let me clarify here. Before I do anything, LTFT -20 when throttle close. I then disable MAF and PE, pull out 20% on VE table across the 20-50kpa to 0-1200rpm section. Run it again it was fine but not perfect.

    Then I enable MAF and PE, do the run again. This time LTFT +20 when throttle close!!!. I'm not sure it bcuz of the MAF or PE, since PE will be enable with 30% TPS.

  7. #7
    Advanced Tuner HawkZ28's Avatar
    Join Date
    Feb 2009
    Location
    Waverly, NE
    Posts
    475
    Try the "Mult by minus 1/2 %" function. See what that does. Not sure if the software you are using has that, though. Otherwise, try pulling 10% and see what happens.
    Hawk

  8. #8
    Potential Tuner
    Join Date
    Sep 2019
    Posts
    1
    Quote Originally Posted by HawkZ28 View Post
    Try the "Mult by minus 1/2 %" function. See what that does. Not sure if the software you are using has that, though. Otherwise, try pulling 10% and see what happens.