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  • Tank venting

    Since my pro-flo2 was installed when I purchased my car I have trying to determine if it is installed correctly. I was under the tank tonight as I am replacing the fuel filter and noticed some tubing connected to the side of the tank on the driver's side which is being used to vent the tank from what I can gather.

    What is proper venting for this system?

  • #2
    "Side of the tank" is not a vent. Vent's are on the top of the tank.
    It might be the fuel return.
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    • #3
      Well a side port that's at the very top of the side of a tank could be for a vent line. It would be helpful to know the year, make and model of the vehicle in question. Also, if you're wondering if the kit has been installed correctly, is it because you're experiencing some kind of problem? If so, what's the problem?

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      • #4
        72 Chevelle. The hose I'm speaking of to clarify is on the side near the top. I have had some issues but likely not related to the tank being vented or not. I do not have a vented gas cap so assuming that it should be vented somewhere but did not see much in the installation instructions.

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        • #5
          If you don't have a vented gas cap. Then most likely you should have 3 lines going to the front of the car.
          2 on the passenger side....3/8" for fuel to the pump, and 5/16" line for fuel return from the pump.
          1 line on the drivers side. For the gas fumes, from the tank, to the charcoal canister. This is the "vent" line.
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          • #6
            That all adds up. I have a box sump welded on the rear underside of the tank for the supply line, then a return line near center front of tank at top, and the vent line is on the drivers side. the vent line is just some coiled tubing zip tied. I've read that if this done their should atleast be a loop near the vent outlet that rises above the top of the tank to prevent siphoning. I should post a few pics. The electric fuel pump is definitely not lower than the sump box. It's about level with the bottom of the tank.

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            • #7
              On home made vents. I like to install a little fuel filter ( metal screen ones works best ) on the line. It helps to keep the bugs out.
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              • #8
                Since I've posted this I've unraveled the current tubing and made a high loop (few inches above top of tank) and brought back down below tank. When I have a full tank I am still getting fuel coming out of the vent which is perplexing. Almost like pressure builds and creates a sipohn. I don't know much high I need to take that loop to prevent this but it leaks and is frustrating. Anyone have run into this issue before?

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                • #9
                  If the tubing is from the side of the tank. It's not a vent line.

                  Vent lines are ontop the tank.

                  Some have a check valve, to stop liquid from coming out of it.
                  Some have a liquid separation box, that send the liquid back to the tank.

                  Whats the Year, Make, and Model of your vehicle?
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                  • #10
                    71 Chevelle. Take a look at the pic from the link. the port I'm talking about is the one on the passenger side. the driver's side port is crimped and the center port serves as the fuel return. I think the chevelles used to have a carbon chamber that one or more of the cents went to. I would consider the port that I am using as the vent at the top.

                    https://www.opgi.com/common/CH28908-lrg.jpg

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                    • #11
                      This is how it came from the factory:
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                      • #12
                        My 64 chevelle has the vent on front right side of the tank at the top. The vent hose is looped higher then tank to keep raw fuel inside.

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                        • #13
                          The 1964 is not the same as a 1971.
                          Around 1966 manufacturers started to redesign the fuel systems. Around 1968 they all whent to a closed system.

                          The tank that ecn113 linked to, and the diagram I posted shows how bad the vehicles were retrofitted back in the 70's.
                          The 3 nipples on the semi-top section of the tank all go to a liquid/vapor tank.....they only needed 1 nipple fitting, but that would have been copying Ford's design with a check valve.

                          Anyway:
                          To properly run a EFI fuel sump on the car. With out doing "welding" modifications.
                          1. Fit a block mounted fuel pump that doesn't use a return line....Edelbrock #1721.
                          2. The sumps vent line goes to the factory return line. Thats installed on the sending unit plate. If their is no return line on the sending unit plate, then get a new plate: https://www.rockauto.com/en/catalog/...395,fuel+&+air
                          3. Run the 3 nipples to the fuel/vapor separator... Basically put it back to stock configuration.
                          4. The vapor "out" line, of the vapor/fuel separation tank, can stay connected to the charcoal canister.
                          5. Don't connect anything to the charcoal canister's output.......you would need to buy, and "test" about 3 factory original parts to properly use the output of the canister. But it doesn't sound like you have the skill to do that.
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                          • #14
                            Here is an update related to this. The drivers passengers side and middle vent are crimped shut, leaving only the driver;s side open which has just been connected to a fuel hose looped high. What I believe has been happening is that when the tank is full the fuel blocks that vent at times while pressure builds behind it. Eventually the pressure burps the fuel through the line and could begin to siphon. I've capped the remaining open vent line and have a vented gas cap. Soon found out it only allows air in to compensate for consumed fuel. I've since drilled a small hole in the cap, attached a line and made a charcoal canister with activated charcoal and stashed it in the rear bumper. I think I'm in better shape given my setup

                            I don't think I've asked this before. What is the proper way to return the fuel with the ProFLo2? My current setup uses a port in the middle where it dumps the fuel from the top back into the tank. Should it be connected to a line that goes to the bottom?

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                            • #15
                              That's a tricky question.

                              When you had a low pressure fuel system. The return was on the top. The fuel returning did not make to loud of a "noise" doing this.

                              Now that you have a higher pressure return system. A complaint that "some" people have is they can now hear the fuel splashing, as it returns into the tank.

                              The fix for this is to submerge the return line at the bottom of the tank. The "trick" is to not have the end of the line next to the pickup intake.....you could pickup warm, aerated fuel....this will kill most electric fuel pumps.

                              So. Basically try it how it is now, and if it makes objectionable noises. Then modify it as needed.
                              At 43,861 MPH Elon Musk now owns the fastest car in this Galaxy

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