Fuel pressure control (Peugeot Eurovans 806)

The fuel pressure regulator constantly maintains the fuel pressure in the fuel line at 3.0 bar. The fuel pressure regulator is installed on the fuel line and consists of two chambers separated by a diaphragm. The upper chamber has a spring that pressurizes the lower chamber and closes the outlet diaphragm. A pressurized fuel stream flows into the lower chamber, which pressurizes the diaphragm. When the pressure exceeds 3.0 bar, the outlet diaphragm opens and excess fuel returns to the fuel tank through the return line.

A vacuum hose connects the upper chamber to the intake manifold so that changes in intake manifold pressure do not affect the amount of fuel injected. This means that the pressure in the fuel line is always a constant pressure, which is higher than the pressure in the intake manifold. The quantity of injected fuel thus depends solely on the opening time of the injector, which is determined by the electronic control unit, and not on changes in fuel pressure.

At idle, when the vacuum pipe is disconnected or the engine is off and the pump is running, or the throttle is wide open, the fuel pressure in the system will be approximately 3.0 bar. Idle (vacuum tube attached) the fuel pressure will be approximately 0.5 bar when the system is pressurized.