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  • In-tank fuel pump

    What are the pros & cons of running a in-tank fuel pump that is Pulse Width Modulation (PWM) compatible, compared to one that is not PWM compatible? Would one be better than the other? Or is it a matter of personal preference?

    I know if I run the PWM pump I do not need to run a return line, and if I run the non-PWM pump I need a fuel pressure regulator with return line and I would have to turn off the PWM in the settings.

    I guess my thinking is with the non-PWM pump, there would always be a full 58psi in the fuel rails. And with the PWM pump there’s could be PSI drops constantly in the lines because of the switching on and off.

  • #2
    The PWM fuel pump control in Pro-Flo 4 is really just for the Edelbrock fuel pump sump. The sump is very small and without PWM'ing the pump, fuel temps can get high. PWM'ing an in-tank pump should really not be necessary. A single in-tank pump with the output capacity to support the power levels attainable with Pro-Flo 4 is not at all an "extreme" case where there would thermal issues. Just about every 800 hp or less V8 on the road with EFI and an in-tank pump is getting around just fine without PWM'ing the fuel pump.

    PWM'ing a fuel pump does not mean you don't need to run a return line. Whether or not you run a return line has to do with how the fuel pressure regulator is setup. If the fuel pressure regulator is under the hood, you run a return line back to tank. A returnless system means that the fuel pressure regulator is either very near or inside the fuel tank but in all cases, you ALWAYS need a fuel pressure regulator.

    With a manifold pressure referenced fuel pressure regulator, fuel pressure is actually always changing based on manifold vacuum (or boost if forced induction). The point of the fuel pressure regulator is to control the pressure that exists between the fuel pump outlet and the fuel rails and injectors. The regulator bleeds off and bypasses fuel to keep the fuel pressure set so in periods of low fuel demand where normally the regulator would have to bypass a lot of fuel to keep pressure down, dutying down the pump with PWM means that the base feed pressure is lowered so less fuel has to be bypassed to maintain the correct fuel pressure but the pressure between the pump and the rails stays the same. That's the point of the fuel pressure regulator.

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    • #3
      So if I run the non-PWM pump, will I be fine with just running the Edelbrock vacuum fuel pressure regulator (17401) with a return line? Or do I need to run something else?

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      • #4
        Yes, correct. Good to go just like that without anything else. What you planning on using for a pump? Be aware that the 17401 is a non-adjustable 58 psi fuel pressure regulator - have you already matched that pressure to a cal you expect to run?

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        • #5
          I am planning on buying the Tanks Inc kit. It comes with the Walbro fuel pump (GPA-4) here are the specs:
          DETAILS

          Electric Fuel Pump Type: In Tank
          Free Flow Rate: 67 GPH / 255 LPH
          Fuel System Type: EFI
          Fuel Type: Gasoline
          Electric Fuel Pump Inlet Fitting(s): 1/4" NPT Female
          Electric Fuel Pump Outlet Fitting(s): 1/4" NPT Female
          Maximum Pressure: 100 psi
          MFG. Part #: GPA-4

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          • #6
            my intank pump is doing just fine over 3k miles on it . its feed stright 12 volts . also have the vac ref fuel regulator .
            73-87 gm trucks is my thing . i have a few of them .

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