Guys. I have to say that you all have been extremely helpful. After the pictures where posted I went back and looked at my German parts book. The 230TE is supposed to have the cone shapped valve number 73 on your diagram. Now I have to go and check and see if I still have the valve and if it is clogged.
It is definently vacuum not pressure buildup. I know a little pressure buildup is normal in modern closed fuel systems but this is actually vacuum. When I undo the gas cap it is hard to pull off because of the vacuum. I can hear the air been pulled into the tank as I remove the cap. I haven't pulled my fuel gauge sendor out yet but I have a feeling it has been deformed by the pressure and the float is stuck.
As someone stated yes my car was retrofitted with the charcoal canister when brought to the states. Of course there is no way for me to know exactly what was done. I do believe that it isn't hooked up 100% correct though. The canister was hooked to the vacuum line for the vacuum advance. If you look at a 190E 2.3 (same engine). The canister should be hooked to a temperature valve in the head and then routed to somewhere on the intake. I am working on fixing that part as soon as I can find a 190E to look at to get it right. I am going to go take a look and see if I do have this cone shapped pressure valve and see whats up.
1985 230TE 5 Speed, BBS, Yokohama, Euro lights just added, 220,000 miles