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1970 Challenger with Sniper System Fuel Siphoning from Vent

Orange Man

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Just a bit of info before I go through the problem. I bought my 70 Challenger from a friend's widow. My friend had a Holley Sniper system put on the 440 Magnum. I am finding they did a sloppy job and took some short cuts. I won't go into that just yet. The problem I am having is that I can't fill the tank full because fuel comes out of the vent. The tank is the Holley EFI tank that comes with the in tank fuel pump. The vent hose has a check valve that I installed because the first time fuel came out of the hose it had nothing on the end and the hose was routed along chassis towards the back and parallel with the tank. I read that the the end of the hose needs to have a vent valve and it needs to be above the top of the tank. The only place I could put it was where the right shock it mounted. The valve is about 6 inches above the tank. The other day I filled up and fuel came out again. 93 octane is expensive and I need to make this a priority to fix. Has anyone else had this problem?

On a side note, my friend bought this car sight unseen out of Florida and there was no history as to who restored it. I found from the VIN that the car was originally a small block SE car. The seller falsely sold the car to my friend as an R/T car. When I got it home, the first thing I looked for was the fender tag and that is missing. The seller did a decent job on the restoration but it is cloned. I bought it right and am ok with what it is.

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Bret Schneider

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Usually when the tank isn't vented correctly the hard part is getting fuel into the tank. Weird that it would come out of a vent that's higher than the tank. The vent valve you're referring to is actually a roll over valve that's designed to vent the tank unless the car goes on it's top in which case it closes. Sounds like you're on the right path with what you've done, but maybe check these links from Tanks out. I've had good luck with their roll over valves.

Fuel Tank Venting
Remote Mount Rollover Vent Valve
 

pschlosser

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You may want to google and research the Holley Sniper EFI conversion. This may not be an issue specific to the Challenger, and it's possible others have run in to this same problem and posted their fixes. Your audience is somewhat limited, here, to mopar-specific topics.
 

MoparCarGuy

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Please post some pictures of what you have for a vent line. The Holley EFI tank is sourced from Tanks, Inc.
There are two vents involved with these tanks. One on the tank and one on the fuel pump. Both of these vents can be tied together and then routed above the fuel tank to the factory fuel vent tubing.
This is what the top of my tank looks like before installation. R is the return line, V is the vent (combined with the tank vent line), and S is the supply to the external fuel filter and on to the fuel regulator and Stealth throttle body.
Tank Connections (1).jpg
My Fuel System.jpg
 

ignition1

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I have installed a couple sniper kits with the Holley EFI tank and have not had an issue with the ‘vent’ spilling fuel. I usually cap off the “V” vent on the fuel pump and only use one vent on top of the tank.

I do have issues sometimes with the fuel coming back out of the neck depending on the pump and when the handle decides to click off, sometimes spilling fuel on my shoes and the floor.

On the ‘cuda there is an in trunk fuel vent thing that mounts through the floor pan that puts the fuel vent way up above the tank. Does the challenger have this also? Maybe the vent needs to be even higher than where you have it mounted.

Maybe the fuel is possibly filling up high enough into the fuel neck, the the handle not cutting off soon enough, vent not high enough to accommodate this, and spilling fuel out the vent.

Also when the fuel spills out of the vent is the tank full?
 

MoparCarGuy

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The fuel vent setup should look like this and puts the vent line way above the tank and trunk floor pan.

1702786439776.png
1702786522344.jpeg
 

Orange Man

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Fuel was coming out of the vent tube just before the fuel pump handle cut off. The 70 Challenger has a vent tube on the side of the neck about 4-6 inches in, before the gas cap. Who ever installed the system, ran the vent line from the in tank fuel pump to the filler neck vent tube. Mopar Car Guy's set up is what I was thinking about doing. This would tie both vent lines together and attach them to the vent tube on the filler neck. That would put the vent lines quite a bit above the tank.

Good information guys. Thanks
 

Bigblue73

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If I was a betting man, I'd say the vent valve is installed backwards. It's a check valve that only lets fluid flow in one direction. The kit refers these as a roll over valve. If the car is in an accident and on its roof, the fuel will have a restriction to not allow gas to free flow from the tank and enhance the possibility of a fire.
 

Orange Man

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If I was a betting man, I'd say the vent valve is installed backwards. It's a check valve that only lets fluid flow in one direction. The kit refers these as a roll over valve. If the car is in an accident and on its roof, the fuel will have a restriction to not allow gas to free flow from the tank and enhance the possibility of a fire.

There is no way to install the vent valve backwards. It only goes one way. The other thought I had was to put a bend in the line like a P trap. Anyway, as soon as I get down to about a gallon of fuel in the tank, I am going to drop it and redo what the piss poor installers did.
 

Orange Man

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Please post some pictures of what you have for a vent line. The Holley EFI tank is sourced from Tanks, Inc.
There are two vents involved with these tanks. One on the tank and one on the fuel pump. Both of these vents can be tied together and then routed above the fuel tank to the factory fuel vent tubing.
This is what the top of my tank looks like before installation. R is the return line, V is the vent (combined with the tank vent line), and S is the supply to the external fuel filter and on to the fuel regulator and Stealth throttle body.
View attachment 116494 View attachment 116495
The venting problem is solved using this method in the photo. Holley was slow to respond but they finally did. The lady at "Tanks Inc" told me that there should have been a Y barb fitting (like in the photo) included in the hardware package of the Sniper system. She said this was so the vent lines could be consolidated into one. I asked why two vents? She said they added the vent tube on the tank because of previous problems with venting. Anyway, I am now hooked on to one line into the filler neck. Thank you all.
 
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