Fuel tank positive pressure

[Freeborn]

My truck:
-1978 FJ40
- Original 2F (rebuilt)
- Chevy TBI
- EGR (and Air injection) deleted
- Vacuum plumbing highly questionable/non-existent

Context:
My fuel tank builds a good bit of positive pressure when I'm driving around. I've figured out that the output of my charcoal canister is plugged. I'm assuming this is my issue.

Question:
What's the best course of action?

1. Do I go through the trouble of plumbing the VCV? If so, is there a generic compatible BVSV available somewhere since it looks like the OEM brown ones are discontinued? Or is it a big deal to delete the BVSV? Or can I just run the output of the charcoal canister directly to a ported vacuum source?
2. Is there an easier way to safely vent the tank? A vented gas cap maybe? Recommended products?

 

[fjc-man]

For starters, you can use an aftermarket charcoal canister.

 

[Freeborn]

For starters, you can use an aftermarket charcoal canister.

Well that didn't even occur to me. Got any product recommendations? (to use or stay away from)

 

[Freeborn]

...maybe also to add clarity...

The charcoal canister output is plugged at the end of the line that would normal go into the VCS on the driver-side wheel well.

 

[hobbes]

Define “good bit of pressure”? There should be a whoosh when you open your fuel cap after driving. If you hear your fuel tank expanding (like a pop) when you drive, like I did, that’s an issue.

In my case, a PO had pulled the evap line to the atmosphere and mud doubers built a nest completely blocking the line. He fixed that issue by drilling a hole in the fuel cap.

You can pull your output line at the canister and see if any air escapes. There should be none, or very little. Working back to the fuel tank, try pulling the input line to the canister. Then try pulling the line after the one way check valve. No air should escape. Then try pulling the input line to the check valve. There should be a slight whoosh. Think 2 psi pressure.

Vented gas caps, like the factory one, let air in. They are not supposed to let air out. Escaping air should go thru the canister. My PO got around that by drilling a hole in the fuel cap.

Good chance you can leave the canister output line vented and not get much fuel smell in the garage if your issue is down range of that, until you can get the issue properly sorted.

 

[hobbes]

Open the output up. See If that fixes the issue.

Edit: if you need to build an EVAP system down range of the charcoal canister there's a good download on the thread below. It's focused on the 2F, but the parts/theory is the same.

How to Desmog an FJ60

forum.ih8mud.com

 

[Freeborn]

Define “good bit of pressure”? There should be a whoosh when you open your fuel cap after driving. If you hear your fuel tank expanding (like a pop) when you drive, like I did, that’s an issue.

In my case, a PO had pulled the evap line to the atmosphere and mud doubers built a nest completely blocking the line. He fixed that issue by drilling a hole in the fuel cap.

You can pull your output line at the canister and see if any air escapes. There should be none, or very little. Working back to the fuel tank, try pulling the input line to the canister. Then try pulling the line after the one way check valve. No air should escape. Then try pulling the input line to the check valve. There should be a slight whoosh. Think 2 psi pressure.

Vented gas caps, like the factory one, let air in. They are not supposed to let air out. Escaping air should go thru the canister. My PO got around that by drilling a hole in the fuel cap.

Good chance you can leave the canister output line vented and not get much fuel smell in the garage if your issue is down range of that, until you can get the issue properly sorted.

"Good bit of pressure" means that it's enough pressure that I can feel the breeze it creates as I remove the gas cap. The tank makes noises every now and then while I'm driving - like it's getting inflated.

 

[hobbes]

I had that, too. If you hear the fuel tank itself expanding, that's too much pressure. Drive it briefly and pull the lines like I said above. That'll tell you where the blockage is. If you need to rebuild the system, checkout the attachment above. You want your fuel tank vapors running thru the canister to keep the smell down. There's no reason not to. I think guys thought it was robbing performance back in the day or something.

 

[fjc-man]

This is either the same circuit layout ( for a 79 ) or pretty similar.

 

[fjc-man]

Well that didn't even occur to me. Got any product recommendations? (to use or stay away from)

It’s probably been 5yrs now since I replaced mine. I think I bought it from Orielly’s? All the parts suppliers sell them. Rockauto?

 

[Freeborn]

Anybody have any ideas for a substitute for the brown BVSV? It looks like maybe there are some out there, but they're pretty spendy. Surely there's something compatible that opens around the same temp (129F from what I understand).

 

[AntFarm]

I recommend getting a new BVSV from city racer. (When he returns from holiday) Don’t get too hung up on the color. They all open up when warm, just at slightly different temps. Used ones tend to crack and break. If you really want to go used, with all the people desmogging their 60s you might inquire over there.

 

[PabloCruise]

...maybe also to add clarity...

The charcoal canister output is plugged at the end of the line that would normal go into the VCS on the driver-side wheel well.

So you mean there is no way for engine vacuum to evacuate the contents of the charcoal cannister?
Vapors can flow in from the tanks, but they cannot be purged out?

 

[PabloCruise]

Anybody have any ideas for a substitute for the brown BVSV? It looks like maybe there are some out there, but they're pretty spendy. Surely there's something compatible that opens around the same temp (129F from what I understand).

Wait, you are running a SBC, yes? IIRC, the BVSV mounts in the thermostat housing of a 2F.
Does your engine have a similar provision?

 

[PabloCruise]

You want your fuel tank vapors running thru the canister to keep the smell down. There's no reason not to. I think guys thought it was robbing performance back in the day or something.

This ^^^.

I think the EVAP system got thrown into the de-smog concept.

People see all those lines and think - "I am just going to get rid of all that crap!".

 

[PabloCruise]

Open the output up. See If that fixes the issue.

Edit: if you need to build an EVAP system down range of the charcoal canister there's a good download on the thread below. It's focused on the 2F, but the parts/theory is the same.

How to Desmog an FJ60

forum.ih8mud.com

Thanks for that link!

I am going to attach the PDF here, if you do not mind?