Fuel Pressure Regulator: Description and Operation

Fig. 5 Fuel Pressure Regulator-3.3L Engine:

The fuel system uses a vacuum balanced, non-adjustable fuel pressure regulator. The powertrain control module (PCM) does not operate the regulator. The pressure regulator sits in the fuel rail (Fig. 5).

The regulator maintains fuel system pressure at approximately 317 kPa (46 psi) with manifold vacuum applied to it and the engine idling. Without vacuum applied the regulator maintains pressure at approximately 379 kPa (55 psi).

A leaking vacuum supply hose can change fuel system pressure. To determine if the regulator operates correctly, check fuel system without vacuum applied to the regulator.

Fig. 7 Fuel Pressure Regulator Operation:

The pressure regulator contains a diaphragm, calibrated spring and a fuel return valve (Fig. 7). The spring pushes down on the diaphragm and closes off the fuel return port. Manifold vacuum applied to the top of the diaphragm acts against the spring pressure while fuel pressure pushes on the bottom of the diaphragm. The combination of fuel pressure and intake manifold open the return port. The more intake manifold vacuum applied to the regulator, the less fuel pressure required to open the return port. System fuel pressure reflects the amount of fuel pressure required to open the return port. System pressure varies with different amounts of intake manifold vacuum.

With low vacuum, such as during wide open throttle conditions, minimal vacuum assistance is available and full spring pressure is exerted to seal the fuel outlet causing. This causes system pressure to increase. With high vacuum, such as during idle, fuel pressure on the bottom of the diaphragm is balanced by intake manifold pressure on the spring side. This results in lower system fuel pressure.