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New Gas Tanks / pressure

400iso

New Member
Joined
Jul 19, 2018
Messages
30
Loc.
Inglewood
Hi Guys,

I replaced the 6-port fuel valve on my 73 Bronco with a 3-port valve recently and also installed a new aux and main gas tank. I noticed that there is a bit of pressure building up in tank. Wondering what you guys recommend to relieve pressure?

Thanks!
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
Do you have the charcoal canister vent system intact? the early caps were vented system and used a different cap than the later models with the charcoal system. The caps on the later models do not vent out through the cap they only let air in. Pressure is supposed to vent through the charcoal canister.
 

Boss Hugg

Contributor
Bronco Guru
Joined
Jun 8, 2010
Messages
2,140
I've never looked at how the 6 port valve was plumbed because mine was bypassed when I got it. But given that I DO understand valves, I'm not sure how you could completely replace a 6 port with a 3 port, unless you used a pair of 3 ports... Please explain.
 

MarsChariot

Contributor
Planetary Offroader
Joined
Oct 12, 2004
Messages
2,469
Loc.
Albuquerque, New Mexico
73 should be vented through the charcoal can. But I can sympathize with you. I have been having pressure build up in the main tank on the 76 the past couple of years, usually after a long highway run or on hot days. The vent line seems to be clear. Even wrapped the exhaust in header wrap in case the heat was warming up the tank too much. Still not certain what is going on. I am working on it. Let us know if you figure it out before the rest of us.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
With the 6 port you are switching 2 tank fuel lines into the main fuel line to the engine. The other 3 ports are switching the tank vents to the main vent. When you went to the 3 port fuel line switch how did you run the vent lines? Did you just tee them all together? You need to tie them into the condensing bottle so liquid fuel drains back to a tank and vapors go on to the charcoal canister or other vent system.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,275
They're not vents on the selector valve. They're return lines that Ford used in '72 and '73 only. And only on some Broncos, such as those delivered originally to certain high-altitude or high expected temperature locations.
The charcoal canister/evap system was independent even with the return line setups.

Paul
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,275
Oh, but if you still have the valve and the little return line manifold from up on top of the engine, save them. Someone would probably love to be able to use them.

Paul
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
Well that really complicates things. Why would they have fuel returns?
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,275
To eliminate vapor lock at higher altitudes and temperatures.

Paul
 
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