SENR9977 21 Systems Operation Section Fuel Injectors g01142467 Illustration 24 Each fuel injector is held into the cylinder head by a clamp around the fuel injector. The fuel injectors are not serviceable but the nozzles can be removed in order to clean the orifice. The fuel injection pump forces the fuel to flow under high pressure to the hole in the fuel inlet. The fuel then flows around a needle valve within the nozzle holder which causes the nozzle to fill with fuel. The pressure of the fuel pushes the needle valve and a spring. When the force of the fuel pressure is greater than the force of the spring, the needle valve will lift up.
When the needle valve opens, fuel under high pressure will flow through the nozzle orifices into the cylinder. The fuel is injected into the cylinder through the orifices in the nozzle end as a very fine spray. When the fuel is injected into the cylinder, the force of the fuel pressure in the nozzle body will decrease. The force of the spring will then be greater than the force of the fuel pressure that is in the nozzle body. The needle valve will move quickly to the closed position. The needle valve has a close fit with the inside of the nozzle. This makes a positive seal for the valve.