tank ventilation

[udo]

Hi together,

the left tank of my 350i has a short rubber tube, I think for the tank ventilation. But this tube is closed with a plug. Has anybody an idea - is it correct or must the tube be open?

After I opend it, the gasoline overflows during the filling of the tank. Now I fixed a long tube, lead it into the trunk (the highest point I can get) and put it into a bottle. But after a short trip the bottle is filled with gasoline. Shit. Whats to do that the tank ventilation works without overflowing gasoline?

Thank in advance

Udo

[brap_brap]

With EFI, shouldn't the tank be preasurised?

[blaineuk]

brap_brap said:

With EFI, shouldn't the tank be preasurised?

no, the fuel returns to the left hand tank, does it only do ot when you have filled up

[udo]

Yes, it only overflows when I filled it up, especially during the last seconds of the filling procedure and after it in quick right turns because of the centrifugal force.

But if I shut the tube, the car only runs about 200 km (although the tank-capacity is more than 50 litres and it needs only 12 litres per 100 km). I think, than it isn`t empty, but the engine than doesn´t get enough gasoline. And sometimes, after 200 km, only 6 litres can be filled up, although I fill it up very slow an carefully. After 6 litres the fuel comes back up the filling-neck. Than, at the next gas-station, after a short drive, it is possible to fill up with about 25 litres!!!?

I think it could be a problem with an "air-back-pressure", and because of that I tried to open the ventilation rubber, but now ... see above :-(

Thanks in advance

Udo

[350zwelgje]

Looks like trapped air related. The connection on the side needs to be closed of (mine is and will stay like that)-probably production related. I have replaced the connecting hoses between the tanks a couple of years ago and never had any filling up problems to the maximum. Perhaps you need to have a look at these connecting hoses (especially the one at the top for filling up, and at the bottom for being able to use all your fuel...). Better to take all the stuff apart while avoiding debris getting in your fuel pump as it is known that after a 'repair' the fuel pump packs up!

Rob

[shpub]

The vent/overflow hose is often blocked off to prevent fuel spilling out but ideally it should be blocked off with a one way valve so that air can enter the tanks if needed but fuel cannot get out. Demon Tweeks sell them for around £40 ish.

The other problem can be that the interconnecting pipes can get blocked and prevent fuel from moving from one tank to another.