Fuel Vapor Liquid Separator Problem

[cuda346pk]

Finally got her back on the road  However had a fuel leak once I parked it. Was coming from the separator in front of the fuel tank, was dripping from the liquid return line. I opened my gas cap and had pressure release and the drip stopped. I have a new correct style gas cap that should vent any pressure. I took off the separator to check for leaks and clean out good. My overfill limiting valve does move however I notice it seals in both directions. I can see where it would vent pressure as it would lift the check ball and go past however it would seem to block ventilation back into the tank. Should it seal like that or is it rust in the valve possibly causing it.

[72cudamaan]

Since no one else has responded I'll take a shot at this. The vapor separator is normally up front by the fuel pump. What
you are looking at ( I think) is the gas tank vent. 4 hoses go into it from the tank (one for each corner) and
then one hose runs up front to the charcoal canister. If I'm right about what you're looking at, there should never
be any fuel in that line, just fumes. If I'm wrong about what you're looking at, post a picture. What are you working
on anyway? That might help too.

[CudamanTom]

Since no one else has responded I'll take a shot at this. The vapor separator is normally up front by the fuel pump. What
you are looking at ( I think) is the gas tank vent. 4 hoses go into it from the tank (one for each corner) and
then one hose runs up front to the charcoal canister. If I'm right about what you're looking at, there should never
be any fuel in that line, just fumes. If I'm wrong about what you're looking at, post a picture. What are you working
on anyway? That might help too.

and

 

[cuda346pk]

It is what you are describing but the fsm calls It fuel liquid  vapor separator and one of the four vent tubes is short and works as a liquid return line to drain any liquid that ends up in  there back. It also has the overflow limiter valve in the outlet port to the charcoal canister that has probably been gone  for 30 years. I do agree it shouldn't retain any fuel but the lines do come straight down from the separator and loop back up to hook on the tank connections, creating a trap for small amount of liquid to remain. Plus I happened to have re routed the vent line to the engine compartment and had it ending lower than the tank. I did find a small hole in the line that was leaking and figured out it was the liquid return line when i pulled it to clean and Check for leaks. I checked the cap vent and it works but it requires a little pressure to make it release. Guess it wouldn't take much pressure in the tank from muffler heat to push any fuel in that line out the tiny hole prior to the cap venting. I have had the car at all kinds of angles on jack stands over the past 6 months so it's easily possible that's how any amount of fuel ended up there. When i took it all apart there wasn't fuel in the separator. I did check again last night after driving and opened the cap and got a release of pressure. Closed it back and reopened it 10 min later and it had built up a little pressure again. No major pressure but i guess it's just enough below the cap vent pressure to but enough to hold the overflow limiting valve closed. That's my theory anyhow.
It's a 72 cuda but has the earlier (I believe) separator being rectangular and mounted just in front of the tank instead of running up through the trunk floor to a long tube vent style. It seemed to be original when I pulled it based on mounting brackets.



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[quapman]

You have the later "fume-catcher". 70 cars had a loop in the trunk along the right wheelhouse which vents into the frame rail, 71's had what looks like a vertical filler neck on the right side, inside the trunk (4 lines in, one return) and mid 72-4 have what you have.

Did you get it to vent correctly? You shouldn't get venting/pressure release when you remove the gas cap.

[cuda346pk]

You have the later "fume-catcher". 70 cars had a loop in the trunk along the right wheelhouse which vents into the frame rail, 71's had what looks like a vertical filler neck on the right side, inside the trunk (4 lines in, one return) and mid 72-4 have what you have.

Did you get it to vent correctly? You shouldn't get venting/pressure release when you remove the gas cap.

I couldn't remember which one was earlier or later, just knew my 72 FSM shows the wrong setup. No it still has pressure when releasing the cap. Not sure what pressure the caps will release pressure but I would certainly think the overfill limiter valve should vent the pressure from the fume catcher to the charcoal canister or just atmosphere since mine is open. I will probably pull the fume catcher and evaporust it to see if the valve will flow any better then. I used carb cleaner and comprssed air and alot of saking to clean it so far. It is not presenting a problem so far since I cut the line down to get rid of the hole there is no leaking either.

[CudamanTom]

Don't know if this will be of the same situation but...
I received a used vent tube for my 71 that goes in the trunk. It has 5 ports, 4 which connect to the tank and the 5th goes to the front of the car to vent in the breather cap of the valve cover.
I blew thru all 5 ports on the vent tube and that 5th port in the tube was clogged. The other 4 were clear.
With this in mind, I knew it would cause a situation the same as yours. Build up pressure and causing a possible problem.
I cleaned it out and it was really rusty inside. With no way to take it apart I sprayed lots of WD-40 in it and ran a wire in and out. Still clogged up so I had to soak it over night before the rust finally broke free the next day.
Anyway, just wanted to share my little story in hopes it will give you and idea or two.
And just to add, there is a lot of moisture that vents out the tank from the gas over a long period of time. Heat causes condensation in the vent tubes in the tank and goes thru the vent ports. I can see ports becoming rusted up over time, like in my situation.
Good luck and hope you figure it out.

Tom

[cuda346pk]

I think that the overflow limiter valve (check valve) must have rust buildup on it keeping it from flowing fully in either direction but like yours u can't see inside. I have sprayed and blasted but seeing no rust coming out. I will be pulling it and soaking it try again now that the rain is here and she will be parked for a few days. Did that 5th port on you'd contain the overflow valve? If so once your freed it did it seal in both directions at all or just one way?

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[CudamanTom]

I think that the overflow limiter valve (check valve) must have rust buildup on it keeping it from flowing fully in either direction but like yours u can't see inside. I have sprayed and blasted but seeing no rust coming out. I will be pulling it and soaking it try again now that the rain is here and she will be parked for a few days. Did that 5th port on you'd contain the overflow valve? If so once your freed it did it seal in both directions at all or just one way?

David,
I would keep at it. try it a couple more times to see if it frees up. Might get lucky.
I don't have a valve that I know of. It's just tubes inside a bigger tube.
Just curious, where did you hear or read of a valve for yours? I've never read or heard any check valve in the vapor vent set-up. But then again, they changed different things at different years.

[cuda346pk]

The factory service manual shows the valve in the line. I have found reference to it on here I believe and other forums. It is what keeps you from over filling the tank. I can hear the ball moving back and forth in mine but it doesn't flow great in either direction. It is designed to close off the vent when the fuel reaches the bottom of the filler neck and that causes the fuel to back up the neck and stop the pump from over filling the tank. It works fine for that. However it seems to be closing off once the exhaust starts heating the tank causing some pressure to build up. It isn't causing a problem, yet but I know it isn't right. I'm gonna soak the entire thing in evaporust and see if I get any rust out.

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[burdar]

Soak it in EvapoRust. That will get the valve cleaned up. You should have a sealed gas cap on it. 1970 with non ECS should be the only car that uses a vented cap. The gas tank on the mid 72-74 cars is vented through the charcoal canister.

The vapor separator allows air flow through it ONLY when the valve is in the middle of it's travel. It blocks flow when it's seated forward or backward.

When the gas heats up with a full tank, some fuel will back up into the separator tank. You should not have liquid fuel in the 1/4" vent line. If you do, something is plugged.

[cuda346pk]

That's pretty much what I came up with too burdar. The liquid was only in the return line that drains back to the tank. Glad to know it will only vent in the middle and should seal both ways. I will soak it to see if it cleans up any more but I guess it is working mostly as it should. Just wasn't sure if it should seal both directions or not.

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