Fuel Problems, gas in vapor line, leaks, scary!

[PHOENIX]

Well awhile back I posted about my vapor canister being full of gas and not being sure where it came from. I have been cruising around with an empty water bottle hooked to the vapor line, which vents the gas tank. Its been getting hotter and hotter here. Well today was the day.

I am on my way to lunch (about 2 miles from work) and start to smell gas. Last time I smelled gas like this the truck died, the carb was flooded. I had the carb rebuilt and though maybe the problem was solved. Maybe the needle and seat was stuck and caused the carb to floow and fill up the canister. Today with the water bottle attached to the line I determined that the gas was coming from the gas tank. Not sure exactly what is happening and thats what I need help on.

My truck now has headers, new cat, and a single 3" exhuast running down the drivers side, over the axle and out behind the tire. The system is very similar to the stock system, but with headers, different y-pipe and 3" exhuast from there out.

My first guess was that the gas tank is getting hot and the gas inside is expanding. It expanded enough for the gas to go into the vapor vent line and all the way to the canister up front. The 24oz water bottle was full of gas and it was leaking out the top and onto the frame and ground. I dumped the gas out and went in to get food. Came back out and the bottle was still empty. I drive back to work and go inside to eat.

After a couple hours I notice a spot under the truck. Its gas leaking from the the tank switch valve. It looked like it was leaking around the clamps, but I couldn't tell for sure and was not about to lay down on the hot asphualt. The valve is broken and stuck on the drivers side so thats the only tank I use. I estimate that it leaked somewhere around 12oz at that location. I checked the bottle again and it was around 60% full (from a 2 mile drive and a couple hour sit!). I dumped the bottle again and put back. I then wondered how much pressure must be in the tank to cause a leak at the switch valve. So I slowly opened the gas tank cap. There was obviously a higher amount of pressure then normal. I put the cap back on and went back to work.

About 30 minutes after that it was quitting time. I came out and checked the bottle again, still empty. Looked at the switch valve and noticed that is still had a very slow drip, much slower then before. I removed the tank cap again and more pressure was released, still more then normally. I decided to leave the cap off for the 6.5 mile(10-15 min.) drive home.

I arrive home and check the bottle, its about 15% full. The switch valve leak was even slower. When I took the gas cap off there wasn't much release.

I assumed that the gas cap is not supposed to be vented, thats what the canister system is for. Am I wrong? Is the gas tank cap supposed to vent the tank?

What do you guys think my problem is?
If it is a gas expanding problem then I'll have to make a heat shield to protect the gas tank from the exhuast pipe. The shield would be similar to the cat shield.

Please help me out guys, thanks!

[Oldtruckfanatic]

I'm not sure without looking up the vapor recovery system on your truck if the fuel cap is vented but What you wrote did make me think of something. Does your truck have the fuel pump with the return on it? the reason I ask is that I once worked on a truck the po had replaced the sending unit on...it was doing a similar thing and after checking hose routing I found the return was hooked to the vapor tube and the vapor tube was hooked to the return. the vapor tube isn't supposed to be submerged in fuel so it's at the top of the tank but the return is beside the pickup tube and in the fuel all the way down to I think half a tank so when the temp went up outside the pressure in the tank forced the fuel from the return tube into the vapor canister because it was in the gas. When I rerouted the lines per the diagram in the manual the trouble went away. This may not be your problem but it's worth a look if you have the return system. Hope this helps.

[boxrodz]

I'm wondering if your fuel valve is contributing to your problem, although I'm not sure why. If I remember correctly, the dual tank fuel valve has some type of vented tube. I don't believe the gas caps are vented.

One other thing, if your valve is leaking from the seam, you may start experiencing a stalled engine especially if you rev the engine like on the highway climb. It seems almost like a fuel pump going out. I'm guessing that the stalling occurs because the fuel pump is pulling in air from the valve leak instead of fuel.

BTW, are all the fuel/vent lines plumb into the valve correctly?

[PHOENIX]

Yes my fuel pump (mechanical) has the return line.

This problems is only a few months old.
I am the only one who touches this truck and nothing with the fuel lines has changed in years.

I really need to inspect the switch valve closer and double check the return and vapor lines at the tank (is this possible without tank removal?).

[PHOENIX]

I ran searches and couldn't find the answer.
How much can gasoline expand?

[MazaM]

Phoenix, have you found a solution? I am having a similar problem.

[79BIG10]

Eddie easy test for you is to take the return line and plug it off. This will tell if the gas is leaking back to the tank and maybe into the vent line like you're having a problem with. I'm guessing it's like oldtruckfanatic mentioned and it's plumbed wrong.

[PHOENIX]

While looking into this a bit it seems my switch valve is not working correctly.
Is it possible for the return gas to go into the switch and send returned gas to both tanks?

When the switch valve stopped working years ago I had $7 worth of gas in the passenger tank. I couldn't switch to it so I just left it. Both gas tank vent lines go into a Y near the switch valve then go to the canister. So if one line has gas in it they both will. This is where the leak at the switch valve was coming from (the vent line Y connection). I decided to see how much gas was in the passenger side tank, which should have maybe 8 gallons. Nope! it had somewhere around 14.5-16.0 gallons. The tank was basically full. So somehow gas has been getting in the tank I don't use and building up, then filling the vent line, because it is lower then the fill hole. The question is how did the gas get into that tank. I have not taken the switch valve apart yet, but I am guessing that the return gas ports are somehow being shared and both tanks are receiving the returned gas. Because I never use the one tank its getting full and causing my fuel leak and gas in canister problem. But if the switch valve was doing this wouldn't it suck gas from both tanks too? Is there a little o-rings in there and maybe only the return side went bad?

How can I hook the switch valve directly to the battery to determine if it is good or not? My tank selector switch inside the cab is new, so I think it is working. When I get under the truck and plug the switch valve in and have someone hit the switch I hear a click, but the little bars inside the switch valve do not move. This is why I believe the valve to be bad and not the switch. But if someone knows which wires to hook directly to the battery to test it direct I would really appreciate it.

I thought I would need to remove the tank I haven’t been using and clean it well before I use it again. But when I was siphoning the gas out of the tank it only picked up a few little particles. I was really surprised I thought there would have been more in there it was almost nothing. Do you guys think it would be ok to go ahead and fill up this tank and use it?

Where is the best place to buy a replacement switch valve?
I remember them being expensive so I might no purchase it right away. I want to make sure this is the problem (and only problem). I plan to hook up the driver's side tank directly (as if I only had one tank) and drive it like this for a while to see if I still get gas in the vent line. If there is a heat problem causing the gas to expand the problem will only be present in the drivers side tank because that is where the exhaust pipe runs by. I don't think this is the problem, but I want to make sure.

[79BIG10]

Eddie it sounds like the whole thing has been plumbed in wrong. I would look at the lines from the tank to the valve. The return line may be returning back into the passenger tank (not used one) from the fuel pump.

I bought mine from a AC Delco dealer for about $85 but that was 6 port and 1 wire and I think yours is the 5 wire. It may cost more. If it's a single wire you can flip the switch to the driver side in the cab and turn the key on but not turned over. Go under the passenger side of the truck where the valve is and take the green wire off. If you hear it click when you touch the wire to the valve then it's working.

[PHOENIX]

It is not plumbed wrong. Nothing has changed in the plumbing for since I have owned the truck (around 10-years now).
Plus I double checked it all, the plumbing is correct. Yes I do have the 6-port with 5 wires. I got under the truck with the hoses unhooked and had someone flip the switch. I was looking inside the ports with a flashlight. It would just click and not move most of the time. But sometimes it would move, and go back, then stop working again. Whenever it went one way it would click a bunch like plastic gears slipping/jumping. Last night I hooked up the drivers tank directly as if there is only the one tank. Im gonna drive it like that for a little while and see if the problem is solved.

What is the green wire; power, signal, ground?

I did find the new ac delco valve (picture attached) for $78 total.
Anyone ever opened one of these up? They have rivets holding the case together. I think I might open it up and check it out inside. Ill post some pictures. If I seen the inside it would help me understand what I am hearing and what is happening.

Thanks!

[boxrodz]

Pho-
Since I replaced my fuel valve (because of a leak at the seam), I've been meaning to drill out the rivets and examine it. I've just never gotten around to it. It's still sitting on the workbench ...

For the valve, you could call Sam Taylor's Buick Cadillac in Florida and ask for Jason Comer in the Parts Department. When I needed a 6-port, multi-wire valve, I got the AC/Delco valve from him. I gave around $60 for it plus shipping. His prices are very reasonable including the shipping fees.

As far as the wiring on the fuel tank selector valve goes (I think):

Pink/Black = Right Tank Sending Unit.
Pink/White = Left Tank Sending Unit.
Pink = Tank Sending Unit wired to the bulkhead connector going to the Fuel Gauge.
Light Green = Right Selector Switch
Dark green = Left Selector Switch

On the fuel tank selector switch:
Pink = Ignition Power wired to Fuse Box
Pink/Black = Ground wired to Bus Bar

[PHOENIX]

Well I took it apart tonight.
A seal on the return side is missing. I couldn't find it anywhere.
I dont believe it fell off during the disassembly.

Anyway here are the pictures of the disassembly:

[PHOENIX]

Last pic:

[boxrodz]

Thanks for the pics, Phoenix.
If I get some time this weekend, I'll have to tear into mine to see what it looks like.

I guess the missing seal on the Return side of the valve could explain why fuel returns to passenger side tank only regardless of the valve position. And, if the passenger side tank is full of fuel, then any fuel returning to the tank may be force to the canister. If, on the other hand, your passenger side tank is magically producing fuel, I'll swap tanks with you.

I wonder what happen to the seal. I wouldn't think that it could be push up thru the fuel lines.

BTW, on mine earlier post, the Light Green and Dark Green wires may be different colors for non-83 models.

[PHOENIX]

Yeah I couldnt find the seal anywhere. Maybe its in the line somewhere. I did blow compressed air through the lines a little while back and they didnt seem to be clogged at all.

[79BIG10]

Originally Posted by boxrodz

For the valve, you could call Sam Taylor's Buick Cadillac in Florida and ask for Jason Comer in the Parts Department. When I needed a 6-port, multi-wire valve, I got the AC/Delco valve from him. I gave around $60 for it plus shipping. His prices are very reasonable including the shipping fees.

Ditto on Jason. I got my ZZ4 from him and is a stand up guy. Really knows his stuff as well.