Have the a fuel pump pressure tested.
do fuel pressure test
Check your fuel pressure at the fuel rail. If the pressure is low, and your filter is not clogged, fuel pump is likely suspect.
Then you have a BAD fuel pump. Replace the pump and filter. If it is higher then 63 LBS. then the fuel pressure regulator is bad.
If there is no fuel pressure and the fuel pump circuit, fuse and relay checks okay.
50 psi
Yes. The regulator is part of the pump module in the fuel tank.
It is most likely on the fuel pump
The 1999 Mazda Miata is a returnless fuel system. It has a Fuel Pressure Regulator in the tank (above the fuel pump), and a snub at the end of the fuel rail.
The fuel pressure regulator is a component connected to the fuel pump module located inside the fuel tank.
Relieve the fuel pump pressure. Remove the fuel tank and on the top is the fuel pump module. Remove the module and replace with a new one.
It is part of the fuel pump module in the tank.