Gas Tank Venting (1 Viewer)

[SoCarCruiser]

I am looking for help with a gas tank venting problem in my 1981 FJ-40. With the cap on the tank slowly builds pressure until fumes enter the cabin (after about half a tank of driving). Unon removing the cap the tank vents forcefully for a long time (ten seconds or so). I am now driving with the cap loose and have no problems with fumes, but would like to fix the fundamental problem. Can anyone help with this?
Thanks

 

[Vae Victus]

Where is the tank on an 81? Inside or underneath?

 

[brian]

us spec it's in the same spot as early trucks....just under the tub not in it.

 

[73FJ40]

us spec it's in the same spot as early trucks....just under the tub not in it.

Below the tub, and under the passenger seat?

 

[brian]

yeap, the hence the floor pan redesign in '79.

 

[73FJ40]

yeap, the hence the floor pan redesign in '79.

Wow. I've been living in the past with my '73 since 1977, and I thought that once they moved it to the back it stayed there.

Learn something new every day... Hopefully I'll remember!

 

[Solace in Solitude]

Does your truck have the evaporator and charcoal cannister fully connected?

Do you have a breather hose from the tank to the filler neck?

Edit: @KY Longhunter 's DIAGRAM may help a bit

 

[brian]

the only fuel tanks in the back, are after market.

 

[Living in the Past]

us spec it's in the same spot as early trucks....just under the tub not in it.

Tank is more than just then just under the passenger's seat starting in 79. It moved towards the center so it's between the frame rails and under the driver's seat as well. 78 and earlier was in the cab under the passenger's seat (LHD) and straddled the frame rail below the tub. So same location front to back but not side to side besides being below the tub. When the tank was moved out of the cab is grew by six gallons over the 73-78 tanks.

 

[SoCarCruiser]

Car is 100% stock. Tank is underneath. All breather hoses are connected.
Thanks

 

[brian]

probably want to actually check the condition of the hoses, the breather is in the cab. if you're getting vapor in the cab, some of the hoses might be in questionable shape.

breather is a bad term...separator is what i wanted use.

 

[65swb45]

Considering the charcoal canister is also involved in handling fumes, you should check its functionality as well.

 

[SoCarCruiser]

Thank you, everyone. I appreciate your help.

 

[Solace in Solitude]

Car is 100% stock. Tank is underneath. All breather hoses are connected.
Thanks

So, you have the evaporator/separator, in the cab and the charcoal cannister, under the hood, and everything is connected properly... Check all hoses, like @brian said, and check the charcoal cannister functionality, like @65swb45 said...

Dry, cracked hoses will allow fuel to escape (doesn't take much for the smell to permeate the cab)...

A non-functonal (or saturated) charcoal cannister will allow fumes to permeate the cab...

"Topping off" the fuel tank is a great way to saturate the charcoal cannister... If that's been a habit, your's or a PO's), a saturated charcoal cannister will cause pressure to build up.

 

[sggoat]

Usu the charcoal canister had a "check" valve coming from the tank. Sounds like this may be the culprit--plugged, or stuck--not allowing vapors to be directed to the canister--thus causing a pressurized tank.---Try removing the valve and see if the issue goes away--

 

[LAMBCRUSHER]

the check valve is inline just after the separator, right? on the 60 series canister, the check valve is integral...