Fuel Injector: Description and Operation

FUEL INJECTORS

Fig. 11 Fuel Injector Location:

Six individual, high-pressure fuel injectors are used. The injectors are vertically mounted (Fig. 11) into a bored hole in the top of the cylinder head. This bored hole is located between the intake/exhaust valves.

High-pressure fuel is supplied from the injection pump, through a high-pressure fuel line, through a steel connector and into the fuel injector. When fuel pressure rises to approximately 31,026 kPa (4,500 psi), the needle valve spring tension is overcome. The needle valve rises and fuel flows through the spray holes in the nozzle tip into the combustion chamber. The pressure required to lift the needle valve is the nozzle opening pressure. This is sometimes referred to as the "pop" pressure setting.

Fig. 12 Fuel Injector Connections:

Each fuel injector is connected to each high-pressure fuel line with a steel connector (Fig. 12). This steel connector is positioned into the cylinder head and sealed with an O-ring. The connectors are sealed to the high-pressure fuel lines with fittings (Fig. 12). The ferrule (Fig. 12) on the end of the high-pressure fuel line pushes against the steel connector when the fuel line fitting is torqued into the cylinder head. This torquing force provides a sealing pressure between both the fuel line-to-connector and the fuel connector-to-fuel injector. The fitting torque is very critical. If the fitting is under torqued, the mating surfaces will not seal and a high-pressure fuel leak will result. If the fitting is over torqued, the connector and injector will deform and also cause a high-pressure fuel leak, This leak will be inside the cylinder head and will not be visible. The result will be a possible fuel injector miss-fire and low power.

Fig. 13 Fuel Injector Spray Pattern:

The fuel injectors use hole type nozzles (Fig. 13). High-pressure flows into the side of the injector and causes the injector needle to lift and fuel to be injected. The clearances in the nozzle bore (Fig. 13) are extremely small and any sort of dirt or contaminants will cause the injector to stick. Because of this, it is very important to do a thorough cleaning of any lines before opening up any fuel system component. Always cover or cap any open fuel connections before a fuel system repair is performed.

Fig. 14 Fuel Injector Edge Filter:

Each fuel injector connector tube contains an edge filter (Fig. 14) that breaks up small contaminants that enter the injector. The edge filter uses the injectors pulsating high-pressure to break up most particles so they are small enough to pass through the injector. The edge filters are not a substitute for proper cleaning and covering of all fuel system components during repair.

The bottom of each fuel injector is sealed to the cylinder head with a 1.5 mm thick copper shim (gasket) (Fig. 13). The correct thickness shim must always be re-installed after removing an injector.

Fuel pressure in the injector circuit decreases after injection. The injector needle valve is immediately closed by the needle valve spring and fuel flow into the combustion chamber is stopped. Exhaust gases are prevented from entering the injector nozzle by the needle valve.