Low fuel pressure with new fuel pump

Fuel and Air Systems

  1. Markzilla88

    Markzilla88 Active Member

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    hey guys, I’m banging my head against a wall on this one and need some advice and guidance.. The car is a 72 demon with a 360. I just installed a new Holley red pump (to replace the current Edelbrock small pump mounted improperly and not flowing well enough) behind the fuel tank, at the same level as the bottom of the tank. I’ve got an inline filter before the pump facing the right direction. All brand new 3/8” hoses and lines to and from the fuel pump are going the right way. I have the line running to another fuel filter in the engine compartment, then to a regulator, then to a fuel pressure gauge, then to the carb (Edelbrock 1405). Once started it only has 2 lbs of pressure. The pre filter before the fuel pump gets sucked almost completely dry. Positioning that filter only helps slightly with increasing the levels of fuel in it. The filter in the engine bay fills to about 1/4 full but after revving the engine some it’s almost empty. The gauge then reads 0, but the car continues to idle.

    I went ahead and bypassed the regulator to see what I was getting from the pump. It holds at a steady 3 lbs of pressure, but the pre filter again runs low (doesn’t ever fill completely up) and the engine bay filter runs about at the same levels.

    What gives?????? I made these changes to a bigger pump to give me significantly more fuel pressure! Not less

    Any guidance would help greatly
     
  2. mderoy340

    mderoy340 Well-Known Member

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    Pulling fuel up and out of the tank does not work. The pump needs to be gravity fed.
     
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    • dano

      dano Evil Handy Man

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      So the pump is equal too or higher than the tank?
       
    • plumkrazee70

      plumkrazee70 FABO Gold Member FABO Gold Member

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      His first post said "behind the fuel tank, at the same level as the bottom of the tank"
       
    • plumkrazee70

      plumkrazee70 FABO Gold Member FABO Gold Member

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      Where is your pump actually located? All of the external pumps I have seen have been on the frame rail.
       
    • Markzilla88

      Markzilla88 Active Member

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      It won’t fit anywhere in the frame rail, and more on that is I couldnt get it below the tank. It’s mounted off the spare tire well from the trunk. It’s behind the tank, but equal to the bottom of the tank. I mean I understand it’s not good at pulling, but the way the sending unit is mounted in the tank, the gas line is pointing upwards. That’s the only pull it would have to do. I’ll try to post a picture of the pump for a better idea.
       
    • MOPAROFFICIAL

      MOPAROFFICIAL Well-Known Member

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      Correct. They are pushers, not pullers.
      Frame mount it lower, also the red pump doesn't need a regulator...and chances are the regulator he is using is a pos " in line chrome dial type from parts store performance section" that no matter where you set them...they put out 2.5 or so... garbage.
      @Markzilla88
      OP should mount it pass side at wheel well bend on frame, or make a plate to mount it.
      Bout the only place it fits.
       
    • 1994redram

      1994redram FABO Gold Member FABO Gold Member

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      I have my electric pump mounted on the frame rail at the highest point, above the axle. The regulator is a cheap Mr gasket dial type. I haven't had an issue with it in several thousand miles. It pulls fuel from the factory tank just fine. I have adjusted the pressure from 4-6.5 for sh!+$ and giggles.
       
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      • Markzilla88

        Markzilla88 Active Member

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        I guess I can try to mount it up there. It’ll certainly be higher then the tank.. the previous owner had an Edelbrock 38gph pump mounted high, and it never made good enough pressure while driving. He says the motor needs to run at 6lbs or else it’ll lean the motor out and ruin it.
        I did bypass the regulator when I put the holley red on there, but still made max 6.5 lbs and then it dropped to 5 after driving it up and down the street twice so I parked it.
         
      • MOPAROFFICIAL

        MOPAROFFICIAL Well-Known Member

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        My '71 swinger had enough room to mount on the frame just before the wheel well, that's forward of the axle
         
      • MOPAROFFICIAL

        MOPAROFFICIAL Well-Known Member

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        Put a gauge on it and report back.
        I don't lie or make things up. Most people never know how bad they are because they dont even have a pressure gauge to know...and an engine will run on very low pressure, it's only sustained high power loads does the lack of psi show its ugly face.

        To the OP, red pump doesn't need a regulator.
         
      • Markzilla88

        Markzilla88 Active Member

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        So theres space issues with mounting it anywhere near the rear axel. It’s an 8 3/4 which is beefier then I imagined it would be. But Behind the axel is the gas tank and air shocks. And in front of the axel theres the dual 3” exhaust tips that end right before the rear axel. There really is no room for it up there I don’t think.
         
      • Markzilla88

        Markzilla88 Active Member

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        I think I may try dropping the tank and inspecting the sending unit. Possibly the sock has come off or is clogging the line. That’s the only thing I haven’t gone in and inspected.
         
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        • 512Stroker

          512Stroker We are all here because we are not all there.

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          Try deleting the filter on the inlet side of the pump. I have had several Holley pumps w/o issues never ran a filter on the pump inlet
           
        • 1994redram

          1994redram FABO Gold Member FABO Gold Member

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          I have a gauge installed. I went 12.80s on a very mild 360 in my dart at 3310 pounds plus driver. It seemed to work just fine. I now have an aluminum head 408 with a bigger cam and I expect to possibly have some fuel issues when I finally get around to tuning it and driving it hard.

          Never called you a liar, merely stating how MY car is setup. It works for me.
           
        • pishta

          pishta I know I'm right....

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          Where is the air pocket coming from in the pre filter? Can you 'burp' it by tilting it up and letting the air bubble go up the line? Air is compressible, but should not knock it down to 3.
          "Installation Note: Should be mounted below the fuel level of the tank for a good gravity feed on the inlet side.

          • For street performance applications
          • Free-flow capacity of 97 gallons per hour / 367 liters per hour
          • Flows 71 gallons per hour maintaining 4 psi line pressure
          • Pressure is pre-set at 7 psi (approximately)
          • Maximum pressure is 7 psi
          • Pressure regulator not required
          Pre pump filter should be a 100 micron, fuel filter at carb should be ~10 micron. These gerotor type pumps can handle particulate well.
           
        • George Jets

          George Jets 1967 Dart 2 Door FABO Gold Member

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          Had the same low pressure issues with this new Holley electric fuel pump, put this brand new one on to replace the same.

          Like 3 psi, cheep electric pump. Going back to manual stock fuel pump when time allows.

          20190701_100225.jpg
           
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          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            I had a red pump mounted above the tank up by the shock towers. Worked just great. He has a bad pump, or a restriction. Fuel sock, strainer, whatever Or it's not getting enough power
             
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            • Markzilla88

              Markzilla88 Active Member

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              I threw on a holley blue and it’s making tons of pressure. Had to regulate it down to 6.5 lbs but it was initially making 12. I think I’ll still drop the tank and clean/remove that sock when I can but so far I’m happy. I was able to take it for a ride and have it not leave me stranded
               
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