gas tank vaccum

[sengen]

My tank is creating a vaccum that restricts gas flow to the engine. I have tried multiple gas caps to improve venting but have had no luck. Any ideas?

 

[El Kabong]

What year is your Bronco & what caps have you tried? Earlier ones use a cap that allows air in to fill the space as fuel is pumped out. On later trucks the air is provided thru the vapor recovery system. If you are using later caps on an earlier truck, or on a truck that has had its vapor system capped off/plugged, it will cause a vacuum in the tank.

 

[broncnaz]

all broncos use vented caps even the later emissions type setups. As air still needs to be allowed into the tank to prevent vacuum you most likely need a new gas cap.

 

[sengen]

It's a 1976. I have tried a stainless steel cap from Wild Horses and the most recent is a chrome gas cap for models 1971-1976 from Bronco Graveyard.

 

[G's Baja Bronco]

suck on them from the inside, does air enter??