fuel problem i think

[whoompa]

ok i checked my fuel pressure it was 20psi and dropping with car on and then shut it off and it went straight to 0 immediatly i knw thats not right car will start up and die then i left for 2 days and car takes awhile to crank but starts and doesnt die im confused i changed fuel regulator but idk what else and where anything else is located plz help