172 Fuel Tank :: Fuel & Engine Control :: Genuine Nissan Parts :: Sentra / NX (B13) 1991-1994 :: CourtesyParts.com
Look at the parts site here. There are check valves and breathers. I just bought the 17370 check valve. then the breather. I did this when I replaced the Fuel filler, hoses and such. I thought that after this many years, these could need replaced.
The gust of vapors when you pull the cap may be just having the tank warm in the sun or something like that. But, those valves should release that pressure.
Chris 92 classic