Is my fuel tank breather blocked?

[danielsprague]

My Hilux has a small black valve on the breather pipe with an arrow pointing out (i.e. away from the tank) which to me indicates that it is a one-way valve to allow air to escape from the tank (i.e. due to thermal expansion of the air in the tank). The trouble is, it does not allow air to come into the tank to replace fuel as it is drawn to the engine. This is evidenced by a rush of inward moving air when removing the fuel filler cap (the cap has no breather / hole). Once, when the tank was really empty, the vacuum was so strong it starved the engine of fuel.

I've blown the the valve myself, and can confirm it only allows air to travel in one direction.

Now, Toyota's being as well designed as they are, I'm wondering what's gone wrong here. Is it that someone has fitted the valve back to front in the breather line? Or is there a problem with the send / return mechanism in the fuel pump?

At present I'm running it without the valve in the breather line, without any problems. No air movement when removing the filler cap.

Any help would be much appreciated,

Cheers

Dan