I pulled this from the service manual. Pages 4-10/11. Looks like both filter and pump have a part to play.
The combination Fuel Filter/Fuel Pressure Regulator
is located along side of the fuel pump as part of
the fuel filter assembly. It is transversely mounted to a
chassis crossmember (left-to-right).
FUEL PRESSURE REGULATOR
The Fuel Pressure Regulator is a mechanical device that is calibrated to maintain fuel system operating pressure of
between 3.7 - 4.1 bar (54 - 60 psi) at the fuel injectors.
Fuel is supplied to the Fuel Filter/Fuel Pressure Regulator by the Electric Fuel Pump directly.
The fuel pump assembly contains a check valve to maintain some fuel pressure in the system when the engine is
not operating.
If fuel pressure at the pressure regulator exceeds a set amount, an internal diaphragm closes and excess fuel pressure
is routed back into the tank through the pressure regulator.
The Diaphragm Pressure Regulator regulates the fuel pressure by means of the return flow (10) quantity to the
fuel tank.
If the pressure rises above the set pressure, the diaphragm is pressed further against the compression spring.
The valve attached to the diaphragm opens the passage for the return flow further. If the pressure drops below
the set pressure, the valve is closed again by the compression spring .