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  • Fuel tank vent

    I want to find something I can use on the fuel tank vent line to eliminate the charcoal canister and long, useless lines that run to the engine bay.

    This summer when I bought my car, the tank would always release pressure when opening the fuel cap, so I assume the canister wasn't doing anything anyway, it must have been clogged or something.

    I'm thinking something along the lines of a check valve that will allow pressure out, and keep the moisture out at the same time. Does the stock system also allow for air to enter to replace burned fuel?

    Basically looking for some input on how to go about this, and what would work.
    This is the last thing I need for the rear end before getting the car back on the ground, I wanted something I could mount in rear near the vent line shown here.

    In Zipties We Trust....

  • #2
    I wish I knew more about the charcoal system too. mines broken (fittings snapped off) and I jsut plugged the lines with a bolt and have been driving with the constant CEL. don't care cause it's a race car anyway, but I need to do something with it.

    My Maxima has the canister under the hood and the line is tied to engine vacuum as well, so the vent line sucks the fumes out of the tank, through the canister, and into the engine.
    I would think that gasoline outgases enough to keep the system from making a vacuum in the tank. you might think about a check valve somewhere in the line- could work. but most racing fuel cells are simply sealed off with a send and return line and an open vent to outside air. those with rollover protection put a check valve in the line to prevent fuel from leaking out if the car is upside down...
    Originally posted by SoSideways
    I don't care what color they are as long as they are LONG AND HARD.
    '04 G35 Sedan 6MT- The DD
    '96 240SX- The Track Toy

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    • #3
      What about a PCV valve on the line?
      It would let pressure out, and nothing in.
      In Zipties We Trust....

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      • #4
        You know what, I think the 240 canister is hooked to vacuum?
        Do any of you guys remember?

        If so, it would explain why my tank was always pressurized when I pulled up to a gas station....boost....lol

        But in any case, wouldn't a PCV valve work fine to vent pressure/vapor?
        In Zipties We Trust....

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        • #5
          Just got a chance to look in the FSM.

          So the filler neck is vented, but only when the cap is off. Makes sense, you need this to refuel.



          However, it looks like the canister line already has a check valve (9).
          Does this mean I can probably just run it somewhere dry (frame rail say), and let it do its thing?

          Last edited by Solo_S14; 03-15-2010, 09:28 AM.
          In Zipties We Trust....

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          • #6
            Alright, I found some good info in the FSM.

            This is from the S14 SR20 FSM, so I'm not sure if the canister itself is the same on the NA KA24.

            To answer my own question, it looks like the stock check valve is well suited to allow pressurized vapor to leave the tank, while freely allowing clean air into the tank to replace burned fuel. Using the stock valve seems to be a good idea.




            Here is the overall system:



            Info:



            And canister.



            In Zipties We Trust....

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            • #7
              I think I'll put a regular vacuum filter on the end of the line, just to keep garbage out, and mount it somewhere that hopefully will stay dry.
              In Zipties We Trust....

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              • #8
                I haven't had this system ever hooked up on the car...what are you really trying to accomplish from it? In fact I ran my 2nd fuel pump wires through the old vent tube haha.
                'Slicks on a car show me you care - broken axles show me you're trying'
                [I]Nitrous Rental Cars - Turbo Festivas - Vehicular Lunacy[/I]
                [SIZE="3"][B][url]www.sloppymechanics.com[/url][/B][/SIZE]

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                • #9
                  I removed the canister and associated lines from the engine bay, and removed the hard lines to the rear. Basically I was just trying to figure out what was left of the system, and what (if anything) I had to do in order to avoid any issues with things getting (or not getting) in/out of the tank.

                  I posted up the pics to help Matt with his system, as he said he didn't know how it worked either. Looks like I'm good to go, as there's a stock check valve, I just want to keep the rubber line dry/clean for a vent.
                  In Zipties We Trust....

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                  • #10
                    Thanks for posting up the info. There's lots of stuff I need to go through on this car like that. I'll be pulling all of the emissions crap off the intake manifold soon too- that'll be a nightmare in itself. I know there's writeups on the other forums about it, jhust haven't had the time or desire to do the research.
                    Originally posted by SoSideways
                    I don't care what color they are as long as they are LONG AND HARD.
                    '04 G35 Sedan 6MT- The DD
                    '96 240SX- The Track Toy

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                    • #11
                      When i did this i just looked at my buddies first gen rx-7. It just had the vent line running up into a dry area and that was it. Sort of like the trans or diff vent lines.

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                      • #12
                        hey another timely bump - can anyone take a pic of the checkvalve?

                        i gotta figure something out, i just plugged my vent, but i could hear pressure inside of it trying to escape, so i popped the cap off and a lot of pressure was released. long track day tomorrow starting at 8am, got to get it sorted before!

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                        • #13
                          You shouldn't plug your vent line.
                          Pressure still needs to escape from there, it's just not going to the canister now.
                          Actually, air has to go in there as well, the valve allows 2-way passage.
                          I put a regular vacuum line filter on there, and routed the line up into the frame rail.

                          This is the best pic I could find in a pinch.
                          Aren't you glad I'm up writing a paper....lol

                          In Zipties We Trust....

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                          • #14
                            i think im gonna plug the vent, and drill a hole in the cap...

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                            • #15
                              That works I guess, you'll just smell any fumes coming from the cap instead of beneath the car......probably no difference.

                              However, the check valve does offer some resistance before the vapors release, you'll essentially now just have a free vent. Check out the 2nd paragraph here:

                              In Zipties We Trust....

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