2003 Subaru Outback

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Replace the fuel filter, check fuel pressure and add a good fuel injector cleaner to the tank !

FUEL DELIVERY
Fuel Filter
The fuel filter located in the engine compartment, is a pressure-withstanding cartridge type. It has a filter element in a metal case. The fuel entering the filter flows from the perimeter of the element to the center of the filter and goes out from there.
Fig. 46: Identifying Fuel Filter (All Models)

Fuel Pressure Regulator
The pressure regulator is installed at the injector end of the fuel supply line. It has a fuel chamber and spring chamber separated by a diaphragm. Fuel chamber is connected to the fuel supply line and the spring chamber is connected to the intake manifold. Fuel chamber also has a relief valve connected to the fuel return line through which fuel returns to the fuel tank. When the intake manifold vacuum increases, the diaphragm is pulled and the relief valve opens to decrease the fuel supply line pressure (or fuel injection pressure). When the intake manifold vacuum decreases, the diaphragm is pushed by the spring to increase the fuel supply line pressure. Thus, the difference between the fuel injection pressure and the intake manifold vacuum is kept at a constant level of 43.4 psi (299.1 kPa) for 2.5L and 3.0L engines and 43.0 psi (294 kPa) for 2.0L engines to precisely control the amount of injected fuel.
Fig. 47: Identifying Fuel Pressure Regulator (Baja, Forester, Impreza 2.5L, Legacy, Outback & Outback Sport)

Fuel Pump
The fuel pump consists of a motor, impeller, pump casing, pump cover, check valve and filter. It is located in the fuel tank and combined with the fuel level sensor into a single unit. The operation of this impeller type pump is very quiet. When the ignition switch is turned "ON", fuel pump relay is activated. Then the motor operates to rotate the impeller. As the impeller rotates, fuel in a vane groove of the impeller flows along the fuel passage into the next vane groove by centrifugal force. When fuel flows from one groove to the next, a pressure difference occurs due to friction. This creates a pumping effect. The fuel pushed up by rotation of the impeller then passes through the clearance between the armature and the magnet of the motor and is discharged through the check valve. When the fuel discharge pressure reaches the specified level, the relief valve opens and excess fuel is released into the fuel tank. In this manner, the relief valve prevents an abnormal increase in fuel pressure. When the engine and the fuel pump stop, spring force acts on the check valve to close the discharge port, so that the fuel pressure in the fuel delivery line is retained.
Fig. 50: Identifying Fuel Pump (Outback 3.0L)

Hope this helps