ENGINE SYSTEMS CONTINUED
Fuel System Continued
6. There are six fuel injectors mounted on the cylinder head. The fuel injectors are an electro-mechanical device.
High-pressure fuel is continuously available to each injector. The engine Electronic Control Module (ECM)
determines the correct time and duration to activate each injector.
A valve inside the injector opens when the engine EC sends a signal to the injector solenoid. The valve
allows high-pressure fuel to enter the injector. The pressure of the fuel pushes on a needle valve and
spring. The needle valve lifts upward when the pressure is greater than the force of the spring.
In the closed position, the needle valve closes the inlet to the injector, and fuel above the needle vents
through the leak-off port. Leak-off fuel from each injector returns from a connection in the cylinder head to
the pressure side of the fuel transfer pump.
In the open position, the needle valv simultaneously opens the inlet to the injector and closes the leak-off
port. This allows high-pressure fuel to flow to the needle and through the nozzle orifices into the cylinder.
The fuel injects into the cylinder as a very fine spray.
The valve closes when the signal to the injector sole oid ends. The fuel in the injector changes to a low
pressure. When the pressure drops, the needle valve closes and the injection cycle stops. The needle
valve and the inside of the nozzle fit close to one another. This creates a positive seal for the valve.
When the solenoid valve is closed, some fuel escapespast the valve in order to vent through the leak-off
port. A certain volume of fuel always flows from the leak-off port.
Figure 11. Fuel Injector.