It should have a positive pressure which is regulated by the evaporative emission system.

good luck

 

It's possible the EVAP canister can get saturated, especially if you keep filling after the pump clicks off. That can make it smell, but I don't think it can obstruct it from relieving the pressure. There should be some positive pressure, but on OBD-1 cars I'm not sure how to test it or what the limits are.

 

Follow up.

I had time last weekend to service the fuel injectors. Replaced the seals and o-rings and cleaned the injectors (lots of gunk I found there!). Unfortunately this didnt resolve the smell issue. Ive checked the evap canister and its not blocked at all. Im not sure if its absorbing vapors or not but im going this weekend to the junk yard to find a replacement canister and see. Ive checked vacuum going to canister and its fine.

What about the intake manifold? I read that the gasket between the engine and the manifold can leak sometimes. Will this cause fuel smell of there is leak somewhere? How do you test for leaks on the manifold?

Thanks!

 

Leaks in the manifold generally suck air in (vacuum leak), not out. You can check for that by spraying brake-cleaner around it while the engine is idling. If it sucks any in, your idle RPM will surge high.