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Old 03-17-2012, 06:35 PM   #1
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Gas Tank Vacuum leak.

My gas tank has four hoses coming from it. Two in the center, fuel line and return line and two vacuum lines, one on each side. I believe both are leaking because my mechanical fuel pump is drawing gas from the tank. I have the tank dropped and replaced fuel lines and vacuum lines. Still not drawing so I think its the two ports coming out of the gas tank. Is there a way to seal them? Like can I put some type of epoxy or silicone around them so they sit tight and don't allow air leaks. My Jeep runs just fine out of a five gallon gas tank thats why I know its not the pump, but the tank. Any and all help is greatly appreciated.

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Old 03-17-2012, 08:13 PM   #2
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Those are the Roll Over saftey Valves. Im not even sure if they can cuase the pump to not pull fuel. Sounds like a cloged fuel line. When was the last time you changed your fuel filter?
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Old 03-17-2012, 08:37 PM   #3
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Those are the rollover valves and should have nothing to do with no fuel.....You either have a bad pump, bad filter or a blockage in the fuel line somewhere..
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Old 03-17-2012, 11:11 PM   #4
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Those are the rollover valves and should have nothing to do with no fuel.....You either have a bad pump, bad filter or a blockage in the fuel line somewhere..
I changed the fuel filter today and replaced the pump last week. when I had the tank off I blew through the lines and air came out with no resistance. I can draw gas up by my mouth. but as soon as I stop the gas goes right back to the tank and the pump cant draw it up. I hooked it up to a 5 gallon gas can and it ran just fine. I replaced the fuel lines today as well, except for the hard lines but there are no holes in them or anything.
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Old 03-18-2012, 06:43 AM   #5
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When you say you hooked up a 5 gallon gas can, did you just put the hose in there to see if the mechanical pump is pulling or did you put the Fuel pickup/sending unit in it. It is inside the gas tank, number 3 and 4 on the above posted diagram.
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Old 03-18-2012, 09:39 AM   #6
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I just put a hose in there. But when I pulled out the sending unit its just a metal tube connected to a large filter and When I draw from the front of the jeep with my mouth it pulls gas up just fine. Do I need to replace the hanger assembly? The gasket around the hanger assembly is tore up pretty good. But if the other 2 lines can leak then that gasket shouldn't matter either.
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Old 03-18-2012, 12:03 PM   #7
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Thats wierd
hmm actually if your drawing gas up by mouth and it goes back down is that the return line?
Maybe your lines are backwards either at the tank or the fuel pump.

But you said when you put the hose in the gas can the pump works fine and the engine runs correct?
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Old 03-18-2012, 12:39 PM   #8
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Sounds like the fuel lines are crossed or you are creating a vacuum in the tank. Try it without the gas cap on. ......Or something is collapsing in the tank,(maybe the filter at the end of the tube) the fuel pump will draw a lot more than you can by mouth
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Old 03-18-2012, 12:43 PM   #9
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I'm gonna try to replace the pump today to see if it was just a fluke pump or something. I'll try it maybe with the return line off. As soon as the pump stops drawing or I stop drawing the gas just flows right back to the tank. So even if the pump was drawing correctly It would always have an issue when starting cause there would be a huge gap from the gas from the pump forward to the gas from the pump back.
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Old 03-18-2012, 04:05 PM   #10
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There is a fuel Vent hose as well.
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Old 03-19-2012, 09:18 AM   #11
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There is a fuel Vent hose as well.
I took some pictures of what I got going on, but I can't figure out how to put them on this thread. I'm going to buy a new fuel pump today just to see if maybe the one I just bought has a defect or something. Last Sunday it was drawing gas from the tank just fine. I still had to drop the tank to replace the lines so it wasn't a huge waist of time. If replacing the pump doesn't work Im wondering if I could wire an electric pump in on a switch, that would probably fix my problem. since I can draw it up by mouth pretty well. Oh also in the diagram is shows 2 different hanger assemblies, I have the one on the left, its the one with out the sending unit. All I have is the tube with the filter. The vent hose is connected to the gas cap.
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Old 03-19-2012, 09:32 AM   #12
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Its kind of baffling really, you blew all 3 fuel lines clear. Hooked up correctly, new filter.

Only thing about an electric pump is a carburator works on very low preasure, you probably dont want more than 2 to 5lbs of fuel pressure or you will flood the carb.
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Old 03-19-2012, 10:34 AM   #13
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Its kind of baffling really, you blew all 3 fuel lines clear. Hooked up correctly, new filter.

Only thing about an electric pump is a carburator works on very low preasure, you probably dont want more than 2 to 5lbs of fuel pressure or you will flood the carb.
Good point. So in other words if this new pump doesn't work I'm screwed. lol. <---that is exactly how I feel right now. The only other thing I can do is buy a brand new gas tank and a new hanger assembly and maybe all new fuel lines and just start from scratch.
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Old 03-19-2012, 12:02 PM   #14
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I don't know if your tank has a valve in the tank to stop the gas from flowing back or if its just the vacuum created by the pump that holds it. It sure seems to be something pretty simple that is preventing you from getting gas to the engine. I assume you have at this point replaced all the rubber fuel lines that could be collapsing. The only other place you could have a problem is in the tank pickup or a bad fuel pump or a bad gas camp but even that would allow some gas to be pumped out before it stopped...
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Old 03-19-2012, 01:13 PM   #15
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For the hell of it you might just replace the Roll over valves in the top left and right side of the fuel tank.
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Old 03-19-2012, 08:28 PM   #16
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Well I pulled off the vacuum line and blew it out with carb cleaner...this resulted in me finding not only a huge clog but about three large holes the length of the tube. I am now looking online for a way to replace all the hard lines. I can't seem to find any for my jeep. 87 YJ. I was hoping to get maybe steel braided lines instead of the hard aluminum lines. I dont want to break the bank on some fuel hoses though but I want to replace all the lines.
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Old 03-20-2012, 09:22 AM   #18
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Thanks man. The factory parts are perfect. Everyone else wants way to much. I'm gonna try our local used auto parts store and if they dont have it I'm ordering from the first link. Thanks for all the help and time. I'll let you know when she's purring again.

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