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Thread: Hellcat Fuel Pump Commanded DC Drop

  1. #1
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    Hellcat Fuel Pump Commanded DC Drop

    Anyone know what kind of diagnostics will trigger Hellcats to drop pump duty cycle in the middle of a pull? Seeing unusual behavior with one that is dropping duty cycle to 53.9% around 125 mph every 1/4 mile pull. Fuel pressure will be in the low 80s and duty cycle 80s and then all of a sudden 53.9% duty cycle while still commanding 80 psi rail pressure and that causes rail pressure to drop to down near 40 psi.

  2. #2
    Advanced Tuner coanan's Avatar
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    Quote Originally Posted by tbrtuning View Post
    Anyone know what kind of diagnostics will trigger Hellcats to drop pump duty cycle in the middle of a pull? Seeing unusual behavior with one that is dropping duty cycle to 53.9% around 125 mph every 1/4 mile pull. Fuel pressure will be in the low 80s and duty cycle 80s and then all of a sudden 53.9% duty cycle while still commanding 80 psi rail pressure and that causes rail pressure to drop to down near 40 psi.
    May or may not be relevant.

    https://www.hellcat.org/threads/in-t...-ideas.231287/
    Last edited by coanan; 05-16-2020 at 09:13 PM.
    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

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    This isn't a gradual drop like happens when running out of pump. It is instant and PCM commands the pump duty cycle to drop. Will go from something like 85 psi to 40 psi in less than a second when it commands this.

  4. #4
    Does it have a BAP? The FPDM will go into limp mode in some cals if it sees voltage beyond a certain threshold for a period of time.

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    Yes. I should have mentioned the problem occurred after BAP but haven't seen others with the same BAP do this so didn't think about it.

    Are the three voltage values in tune these thresholds? I thought about maxing out the max voltage one but wasn't sure.

  6. #6
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    Looked more at the tables HP Tuners has defined for fuel system and don't see anything. I really wish they had it defined. The voltage thresholds I mentioned were 16v max so can't depend on that being enough really unless you did something like limit duty cycle and upward adapt so it never commands that much. Commanding lower fuel pressure I guess might work too but would hate to have to do that.

    Have you seen these settings in different software maybe so we could get HP Tuners to add them. This car did have a very weak factory pump compared to others I've done and was dropping fuel pressure to mid 60s on 93. The BAP fixed the issue but it is still commanding pretty high duty cycle so FPDM is outputting high voltage combining that with the 21v BAP.

    This makes me really nervous about using BAP if we can't override the setting that causes this to happen because it might be fine at first then start to occur later on. I can't believe they would have something like this in the calibration and not even set a CEL light when it happens. If it is because this pump started out pretty weak so is now having to use a lot of the voltage provided by the BAP it could happen just the same where one is fine at first and pump fades over time or it's making more boost when cold and then it does this.

    Thanks for the help
    Last edited by tbrtuning; 05-17-2020 at 10:13 AM.

  7. #7
    Advanced Tuner coanan's Avatar
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    Quote Originally Posted by tbrtuning View Post
    Looked more at the tables HP Tuners has defined for fuel system and don't see anything. I really wish they had it defined. The voltage thresholds I mentioned were 16v max so can't depend on that being enough really unless you did something like limit duty cycle and upward adapt so it never commands that much. Commanding lower fuel pressure I guess might work too but would hate to have to do that.

    Have you seen these settings in different software maybe so we could get HP Tuners to add them. This car did have a very weak factory pump compared to others I've done and was dropping fuel pressure to mid 60s on 93. The BAP fixed the issue but it is still commanding pretty high duty cycle so FPDM is outputting high voltage combining that with the 21v BAP.

    This makes me really nervous about using BAP if we can't override the setting that causes this to happen because it might be fine at first then start to occur later on. I can't believe they would have something like this in the calibration and not even set a CEL light when it happens. If it is because this pump started out pretty weak so is now having to use a lot of the voltage provided by the BAP it could happen just the same where one is fine at first and pump fades over time or it's making more boost when cold and then it does this.

    Thanks for the help
    Maybe same issues? contact posters a see what they did.
    https://forum.hptuners.com/showthrea...a-boost-a-pump

    https://forum.hptuners.com/showthrea...-Pressure-Drop

    Wiring
    https://www.hellcat.org/threads/boos...-18853&slide=0
    Last edited by coanan; 05-17-2020 at 12:17 PM.
    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
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    Any update on if there is any solution for this other than just limiting duty cycle going to pumps? I have tried things like disabling all fuel related torque management and it doesn't make a difference

  9. #9
    Personally I?ve never messed with those 16v thresholds. Either upgraded the fuel pumps to not need bap anymore, switch to a lower voltage bap or use an adjustable voltage bap from JMS. These were all better solutions anyways at the time and the voltage parameters weren?t available in my cal to mess with when I faced these issues myself and a few other cars I was tuning at the time.

  10. #10
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    They went ahead and went dual pump. Was better at limited duty cycle with the BAP than stock but really not getting the benefit of the BAP that way and it just wasn't enough. Until I see these parameters defined in tune where I can say for sure I won't have another car randomly do this I won't be recommending BAP