Fuel System

Theory and background

• The fuel tank holds the petroleum, the petrol is pumped through the fuel filter to the fuel rail with the fuel pump. The petrol is supplied from the fuel rail to each cylinder at the right time by the fuel injectors. The fuel injectors are solenoids that are controlled by the car's CPU. The CPU calculates how much fuel is needed.
• The pressure in the fuel rail is regulated by the Fuel Pressure Regulator. The fuel pressure regulator is controlled by the vacuum in the intake manifold. If there is a high pressure vacuum on the regulator it opens up and redirects some of the fuel back to the fuel tank via the return line. As the load of the engine increases the vacuum decreases closing the regulator which increases the pressure in the fuel line and that increases the amount  and pressure of the fuel that is supplied by the injectors. 

Procedure for experiment 

• With the engine idling we measured the No Load vacuum from the intake manifold to be -11 psi and the Fuel pressure to be 40 psi
• The second test we did was to simulate the engine being Under Load. While the engine was idling we disconnected the vacuum hose from the intake and measured the vacuum to be 0 psi and the Fuel pressure to be 50 psi

Reflection on experiment


If the engines revs increase the vacuum in the manifold gets less so the regulator allows less fuel to run back to the tank and it also increases the fuel pressure in the fuel line which forces more fuel through the injectors at a higher pressure.