7.5 Fuel Pressure Tests and Specifications

Although the quantity of fuel delivered to the engine is controlled primarily by how long the injectors are open, fuel pressure also has some influence. The fuel pressure created by the fuel pump is regulated by a diaphragm-type pressure regulator mounted to the end of the fuel rail.

A vacuum hose connected to the top of the regulator helps to control the fuel pressure as a function of engine vacuum. When the throttle is opened and vacuum drops suddenly, fuel pressure increases slightly to richen the air/fuel mixture for improved throttle response. For more information on the pressure regulator, see 4.4 Fuel Pressure Regulator.