No the fuel tank should not be under pressure. The fuel line should be under pressure. When you open the gas cap, there really should not be any pressure, if you do have, then something is not working right.
drivers side rear by the distributor under the wiring harness. follow fuel line from under side
There is a low pressure fuel pump in the gas tank, and a high pressure in-line fuel pump located on the under-carriage beneath the drivers seat
regulates fuel presure at idle or under load so you dont get to much or too little fuel
The 1997 Nissan Pathfinder does not have a schrader valve. If you want to test the fuel pressure system (fuel pump, lines, pressure regulator) you have to insert a 'T' in the fuel line under the hood and connect a fuel pressure gauge to the 'T'.
The fuel pressure regulator controls fuel pressure at the fuel injectors. It uses vacuum pressure to control the pressure. It is positioned on the end of the fuel rail. If they leak, fuel will go into vacuum line causing hesitation on start-up and the smell of gas at exhaust. Warning, Fuel is under pressure. Disconnect battery and release pressure before replacement.
Goto the Fuel rail under the hood. it sits on the passenger side of the engine. It will have a black cap on it. NOT the A/c line. it's on the Fuel line. remove the cap and it looks like a tire value stem. Push it in and the pressure will be released.
It is a returnless system. When the fuel leaves the tank it is already at full pressure. The regulator is inside the fuel sending unit (inside the fuel tank, located under the back seat)
Approximately under the steering wheel. Make sure the car is cold, and expect some fuel to leak as the system is under pressure. It helps to have something to plug up the fuel line with (like wooden plugs) to keep the gas from draining out of the fuel line.
under the upper plenum of the intake manifold it is round and is bolted to the fuel line and has a vaccum line attached to it. you need to remove the upper plenum to access it
you hook up a fuel pressure guage to it to check the fuel pressure
The larger line is the pressure line, the smaller line is return.