Hi all:

My 95' 850 turbo always create vacuum of fuel tank , then at bottom of fuel tank close to fuel pump make 'hiss' noise .

If I open fuel filler cap & let air in , the hiss noise will gone .

I had try to figure this might cause something wrong of my EVAP . I check the pipe from charcoal canister while engine running :

(1) The pipe from fuel tank to canister , I smell fuel odor from it , no obvirous pressure .

(2) The pipe from EVAP valve to canister , it had vacuum preesure while engine is hot , the evap valve is open , seems is ok .

(3) if I block the pipe from fuel tank to canister , hiss noise gone .(I think there should be connect a one-way valve to the pipe from fuel tank , and the value to breath fresh air but not let fuel go out .)

Does this mean there is something wrong with my charcoal canister ?

Now I just block the pipe , if I can't make sure canister is fail , I will just connect a one-way valve to fuel tank vent pipe ..... this should be a simple solution but it might not good for environment.

And , if I want to replace canister , can I just use other vehicle brand/model's canister that cheaper than original volvo part ?

Thanks!!

Warren