Curby

OK, here goes. I am leaving for the Hot Rod Power Tour early in the morning and I want to fix the issue with my fuel tank vent before I go. here is the reason:

1. Big Block NOM GM ZZ454 engine with EZ-EFI fuel injection system.

2. New electric fuel pump with braided fuel supply line to FI.

3. Using old fuel supply line as a return line from fuel regulator to old tank vent connection (The vent connection is larger than the return connection).

4. The car had a tank in it with no vent or return connections, and I swapped it for one with both.

5. Using old return line as a vent for tank, but no charcoal canister at end. It is just open to the engine bay now.

6. No vent filter thing-a-magig on the car. I ordered one from The Last Detail, but it has not come in.

7. The car has a vented fuel cap.

8. When I fill all the way up, there is a good chance that the current set-up can siphon fuel out of the return line fitting and dump in the engine bay (It did it once already). Right now, I am just not filling up the car all the way, but I am fixing to drive the car 3,000 miles in 10 days, and wanted to be able to utilize the whole tank.

I wanted to just plug the line until I can get the right part in and plumb it correctly, but I don't know if the vented cap will do what I need it to do. Has anybody else been in this situation and come up with a good solution?

There was no vent before with the electric fuel pump and carb, but I was only running about 6# of fuel pressure before, where I am running 45# of fuel pressure now.

is there another kind of check valve or something I can get at a local parts store that will work on the vent?

Am I good to go with just the vented cap?

noonie

If you cap vent works, you can just plug it.

Does your tank have the internal bladder?

...Roger...

The vented cap will work. What line is siphoning ?

Curby

It does not have a bladder in it, but I did find a few leaves and a dried up chameleon in it when I pulled it out of my parts stock.

noonie

The bladder tanks have two vents, one for inside the tank and one for between the tank and bladder, that why I asked.

...Roger...

You can not use the old fuel supply line as a vent or return if it still goes to the bottom of the tank.

Curby

The original return line connection on the passenger side of the tank is connected to the original fuel return line running to the location of the original mechanical fuel pump. This is the line I am using for the current vent.

The original vent line connection on the driver's side of the tank is connected to the original fuel supply line and is running to the new fuel pressure regulator. I am using this as the fuel return to the EFI system. I did this because the connection on the tank is larger for the vent than it is for the return.

The original vent line running from the tank to the charcoal canister is abandoned. I removed the charcoal canister to mount the EFI computer in it's location. It was abandoned in place by the previous owner.

if I can just use the vented cap, then I can plug the line and my problems are solved. I was concerned that the vented cap may not be adequate for the pressures created by the FI system.

Mike Ward

The amount of pressure downstream of the fuel pump is irrelevant. The tank needs one vent to allow air into the tank to replace the consumed fuel and that's it. Sounds like you presently have two.

...Roger...

I think you have already firured out what your going to do but this is the part that has me concerned. The return from the fuel pump (pass side of car)and the vapor/vent line (drivers side) should both just dump into the top of the tank , no way should they be able to sustain a siphon once the fuel is below and away from the inlet.
Am I missing something or is there a nipple that dips down in the tank ?

Mike Ward

Well I'm sure confused. Who's on first again?

...Roger...

Good One

cardo0

Using the old vent connection at the top of the tank as a return creates a lot of vapor as the returning fuel dumps and splashes into the tank. Better to use the old return connection on the p-side as it should return fuel under the level in the tank and minimize vapor creation. Don't know why the 1/4" return can't handle the return flow. Did u read something in the instructions that said it needed a larger line? For example the return line on my '94 Z28 up at the regulator is fairly tiny - norm press ~ 40psi. I know its only a sb but the return should not need to pass large amounts of fuel at high pressure.
If u are using an vented cap then a vent anywhere else is not needed and can be plugged - u can plug the line to the charcoal cannister as it can't do much now with a vented cap. The vented cap just fits loose on the tank (no valve mechanism here) and does not seal - i believe u can make it rattle - and should handle any vapor pressure produced from your electric pump. Remember the top of the tank will only see vapor pressure - no liquid - and should easily vent off. It sounds like the PO changed it to vented cap.

Where is the new supply line connection on the tank? FYI, it sounds like u are using the old supply connection at the bottom - nothing wrong there but i would have mounted the fuel pump behind the tank to ensure line is filled to the pump when under hard acceleration.

Also FYI, solid line is much more reliable than any flex - even braided SS - and should be used as much as possible. Once u learn how to mach double flares it gets to be fun making custom fuel lines.

Hope this helps,
cardo0

72LS1Vette

I'm not 100% sure what you are talking about but it sounds similar to what I did with my fuel system for the LS1. I used the evap line on the driver side for the return line from the C5 filter/regulator, plugged the original return line and used a vented filler cap. I only have ~500 miles on the car but so far I have seen no problems related to the fuel system.



Rick B.