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Thread: is it possible for s/c to suck open the throttle?

  1. #1

    is it possible for s/c to suck open the throttle?

    6.1 forged and camd, 2.6L s/c
    at smooth part throttle acceleration, around 2500 the throttle just jumps open and goes nearly full boost, sometimes spinning the tires.
    in the log it does it 3 times and you can the accelerator pedal is fairly steady. i'm just accelerating from a stop, not on it hardly at all.
    if i keep app volts around 1 volt, it doesn't do this, but 1.2 and up, i get this every time.
    all i can figure is it's getting close to closing the s/c bypass valve and then it does and from there s/c just sucks super hard.
    i don't really think that can happen as the motor in the throttle body is probably really strong and loaded with gear reduction, but no matter what i do in torque management driver demand power % request and its inverse table. i can't get throttle to behave differently.
    if this is no way mechanical (sucking the blade open), then where else do i try to tame this?
    help please.
    Attached Files Attached Files

  2. #2
    Advanced Tuner coanan's Avatar
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    Quote Originally Posted by [email protected] View Post
    6.1 forged and camd, 2.6L s/c
    at smooth part throttle acceleration, around 2500 the throttle just jumps open and goes nearly full boost, sometimes spinning the tires.
    in the log it does it 3 times and you can the accelerator pedal is fairly steady. i'm just accelerating from a stop, not on it hardly at all.
    if i keep app volts around 1 volt, it doesn't do this, but 1.2 and up, i get this every time.
    all i can figure is it's getting close to closing the s/c bypass valve and then it does and from there s/c just sucks super hard.
    i don't really think that can happen as the motor in the throttle body is probably really strong and loaded with gear reduction, but no matter what i do in torque management driver demand power % request and its inverse table. i can't get throttle to behave differently.
    if this is no way mechanical (sucking the blade open), then where else do i try to tame this?
    help please.
    People call that "The light switch effect"

    https://www.lxforums.com/board/power...ter-surge.html

    https://forum.hptuners.com/showthrea...ng-adjustments
    Last edited by coanan; 10-24-2020 at 09:20 AM.
    2018 Trackhawk PCM/TCM tune by Dusterhoff.
    Flex Fuel, MMX faux 95mm TB, GripTec 2.85, 10% ATI lower, FIC1200, ARH 1 7/8 w/cats, 180 T-stat

    13 Chrysler 300S, RAM BGE 412 stroker, cam motion 232/246 619/619 118 +4, ATI 18% OD pulley
    Whipple Gen5 3.0, 2.50 upper pulley, Smooth Boost controller, FIC 1200 inj. Nick W 108mm TB, FORE dual return fuel system, E85, FTI 2800 stall(SRT83380), SHR WAR Viking trans and valve body, Getrag 3.73, 1 7/8 kooks w/hi-flow cats, 3" Magnaflow Cat-back 943rwhp

  3. #3
    so you didn't work in driver demand tab, you did everything in the electronic throttle area?

  4. #4
    Advanced Tuner coanan's Avatar
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    Quote Originally Posted by [email protected] View Post
    so you didn't work in driver demand tab, you did everything in the electronic throttle area?
    I reworked driver demand. Most of my stuff is trial and error, not a genius with this stuff. Read and experiment is all I can say.
    2018 Trackhawk PCM/TCM tune by Dusterhoff.
    Flex Fuel, MMX faux 95mm TB, GripTec 2.85, 10% ATI lower, FIC1200, ARH 1 7/8 w/cats, 180 T-stat

    13 Chrysler 300S, RAM BGE 412 stroker, cam motion 232/246 619/619 118 +4, ATI 18% OD pulley
    Whipple Gen5 3.0, 2.50 upper pulley, Smooth Boost controller, FIC 1200 inj. Nick W 108mm TB, FORE dual return fuel system, E85, FTI 2800 stall(SRT83380), SHR WAR Viking trans and valve body, Getrag 3.73, 1 7/8 kooks w/hi-flow cats, 3" Magnaflow Cat-back 943rwhp

  5. #5
    Advanced Tuner f.creek-ranch's Avatar
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    Try to disable pedal adaption.

  6. #6
    hmm, thought i had that off already.
    coanan, here's a file i did a lot of what you said in the lxforums post, but it's still doing it.
    will you have a look?
    Attached Files Attached Files

  7. #7
    Advanced Tuner coanan's Avatar
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    Quote Originally Posted by [email protected] View Post
    hmm, thought i had that off already.
    coanan, here's a file i did a lot of what you said in the lxforums post, but it's still doing it.
    will you have a look?
    Wish I knew enough to really help. Look this tune over. E-force running 8psi, small cam and tuned by a reputable tuner. Look at all airflow stuff and timing.
    Attached Files Attached Files
    2018 Trackhawk PCM/TCM tune by Dusterhoff.
    Flex Fuel, MMX faux 95mm TB, GripTec 2.85, 10% ATI lower, FIC1200, ARH 1 7/8 w/cats, 180 T-stat

    13 Chrysler 300S, RAM BGE 412 stroker, cam motion 232/246 619/619 118 +4, ATI 18% OD pulley
    Whipple Gen5 3.0, 2.50 upper pulley, Smooth Boost controller, FIC 1200 inj. Nick W 108mm TB, FORE dual return fuel system, E85, FTI 2800 stall(SRT83380), SHR WAR Viking trans and valve body, Getrag 3.73, 1 7/8 kooks w/hi-flow cats, 3" Magnaflow Cat-back 943rwhp

  8. #8
    Tuner in Training
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    You can log commanded throttle actuator to convince yourself it's actually commanding the throttle to open. Also, it wouldn't make sense for the s/c to be pulling it open. You can't make a whole lot more vacuum than an engine already makes.

    I'm pretty convinced the Dodge ECU's just do this and there's almost nothing you can do about it. Once you hit about 1 bar, the throttle just opens up very fast (which would make sense if it wasn't forced induction). You can sort of trick it into improving things a little by changing the slopes of the airflow models, but I can't get this effect to actually go away, and I don't think we'll ever be able to without a custom OS. I could be wrong, but I've poured probably 100 hours into making this go away and have drawn a complete blank on success. Definitely got things a lot better through the airflow tables, but it still has an annoying surge into boost, and I can see it in the logs.

  9. #9
    Advanced Tuner
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    Totally can be tuned out...look over some of my older posts (I have posted example tunes) and you should find enough to work it all out.
    I love it when tuners say "that is as good as it gets because the Dodge PCM sucks", its just they don't understand how it works or how to tune it....
    And I aint no genius...early days had me stumped too but many, many frustrating hours/days/weeks/months later and it started to make sense and drive/go the way it should.
    It is not just one thing but a combination so getting that right makes it harder (but not impossible) than simpler PCM's.

    Quote Originally Posted by christensent View Post
    I'm pretty convinced the Dodge ECU's just do this and there's almost nothing you can do about it. Once you hit about 1 bar, the throttle just opens up very fast (which would make sense if it wasn't forced induction). You can sort of trick it into improving things a little by changing the slopes of the airflow models, but I can't get this effect to actually go away, and I don't think we'll ever be able to without a custom OS. I could be wrong, but I've poured probably 100 hours into making this go away and have drawn a complete blank on success. Definitely got things a lot better through the airflow tables, but it still has an annoying surge into boost, and I can see it in the logs.
    Last edited by Hemituna; 10-30-2020 at 03:30 PM.

  10. #10
    Raise your WOT Pedal Thesh to 3.0 v before you make tons of adjustments.

  11. #11
    Did you ever figure this out? I'm having the same issue but with a procharged 2010 manual 6.1 Challenger...nothing seems to fix it. At the end of a dyno pull tps drops to 40% and stays there as commanded. Pedal at 0


    edit...this is not really similar actually...disregard
    Last edited by UMSTuning; 11-06-2020 at 03:25 PM.