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Thread: 3V 2010 F150 using "Dashpot" while idling stopped.

  1. #1
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    3V 2010 F150 using "Dashpot" while idling stopped.

    I'm starting a separate thread on this specific issue to see if anyone else has seen it; I didn't want to bury it in another longer thread. It was my understanding that Dashpot settings where only used while moving and off the throttle but logging a '10 F150 with the 3V it doesn't appear thats correct. I start the truck, it goes into RPM controlled idle after it stabilizes, when I hit the throttle then let off it goes to "Pre-Position" (which I assume is Dashpot Pre-Position) then "Dashpot" control. The problem is the "Dashpot" setting doesn't appear able to keep the throttle open; blade position drops as low as 1.7% once it idle goes into "Dashpot" control and the motor dies...what gives?

  2. #2
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    Here's a log and the corresponding tune showing whats going on. Anyone?

    b1.hpl
    1-7-19 # 8.hpt

  3. #3
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    For anyone else that may go down this same arduous path; its all about torque curves. I don't know why the motor is idling on the dashpot settings and nothing I do will change that but until the torque curves are lowered down in the RPM (1,000-750 rpm at .4-.5 load dropped as much as 150 ft/lbs) nothing else matters. Once the torque curves where dropped I was able to control the idle with dashpot and idle airflow settings.

  4. #4
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    What made you change your throttle angle min to 6?

    Your dashpot decay has airflow that are far too great. I've set these up with the axis highest value being 3 lb/min
    axis values
    0.00999999977648258 0.0500000007450581 0.100000001490116 0.150000005960464 0.25 0.5 0.600000023841858 0.699999988079071 0.800000011920929 1 1.5 2 2.25 2.5 3

    The cell values begin at .005, and the highest have mine Is .3 on the bottom cell.'

    Dashpot minimum is minimum. You have it's minimum set to 2 lb/per min at 25 rpm, 175 rpm, 2.2 at 500 RPM. You need to rescale the RPM 0 700 1250 3000 5000. first airflow should be extrememe low at zero RPM. 650 could have .6, 1400 .82 lb/min etc

    Dashpot Preposition adds more to the airflow. Yours are set very high. it's added to the other airflow tables, which are also pretty high in airflow for idle. Airflow (Drive) has 700 RPM should be receiving 1.77 air.
    Example of Idle Airflow Drive on a cammed mustang
    .lb/min Airflow
    500 0.928699970245361
    600 0.952400028705597
    700 1.04510009288788
    800 1.06789994239807
    900 1.08711802959442
    1000 1.12118113040924
    1200 1.16721367835999
    2200 1.6586000919342
    2570 2.13699984550476
    3190 2.93210005760193
    rpm

  5. #5
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    Adding to what was posted above, You probably want to set your idle airflow multiplier tables to 1 instead of 1.1 at the cells where the engine run time is highest and the engine coolant is at operating temperature.

    extra info on dashpot
    https://www.youtube.com/watch?v=zJuzhLorW1A

    This is a video of a mechanical dashpot on an old carb. application. This is what these tables are attempting to do to your throttle blade. You are attempting to slow engine deceleration down to have a smoother return to idle. Pre-position is adding airflow it holds the blade open slightly, this prevents rapid decel of the rpms and stalling and it can also improve emissions. Once at stable idle RPM it should no longer be under dashpot control. you want the dashpot decay to remove the airflow it had added fast enough to return idle control quickly, but not so fast it overshoots its goal. With modern control systems and DBW throttle bodies, you can have a much faster engine decel from reduction of airflow and still prevent stalling, you can also adjust for when the car is engine braking but not decelerating or is decelerating, improving engine braking with out effecting other conditions.
    "We can never be right, we can only be sure that we are wrong"- feynman