B234FT Fueltank EVAP System

Hey guys..

i got some Problems with vaccum in my Tank. Sometimes that big that my Mainpumpe surges due to Air in the System.

I have a 960 TB fitted to a 16v Plenum which has the EVAP Ports on it but also the TB. Due to it is LH2.4 i closed the TB ports and used the OEM ones on the Plenum but now i had a small brainstorm about it and my thoughts.. how should the EVAP membrane work when both hoses are connected to the same pressurechamber? There is a Pic which clearly states that one of the hose should be installed infront and the other behind the TB?

How did you other 16v guys get rid of that Problem?

Will Post some pictures later..

As far as I know the b234F engines I've seen use the ports on the throttle body. They make ported vacuum which gradually increases with the throttle opening. The small port opens the purge valve and the large port sucks in the fumes.

My 1989 740 GLE with B234F actually had an electronic purge valve.

The old way would have been to use a vented cap. But these days you need to figure out what you need and fix the issue.

What does your charcoal canister look like?

The one on my 240 has a tank port on top, an open (atmosphere) port on bottom, plus a purge valve assembly on top. The purge valve has a small and large port. The small port opens the valve, to let the fumes get sucked out through the larger port. If you're getting tank vacuum with this style, something's plugged - the canister is flow through from tank, through charcoal, to atmosphere. When the purge valve is opened, it pulls air from atmosphere, through charcoal, to throttle body.

On a 240 throttle body, the 2 evap ports are on the air filter side of the throttle butterfly -- i.e. no vacuum at idle. They go direct to the small and large purge valve ports on the canister.

how is the fuel cap? Is there lots of vacuum in the tank being filled when you take the cap off?