Common Rail Fuel System Operation The high-pressure fuel line to the injectors is double walled with an air gap between the stainless steel inner tube and the outer copper protective tube (Refer to page 44). This air gap is also a vent from the injector providing early warning of poor injector C-E Ring sealing. The injector has a vent hole drilled in the body from below the lower O-ring land out through the injector arm to the high-pressure line joint surface, which aligns with the air gap in the high-pressure fuel line (Refer to page 31). The injector is retained in the cylinder head hole tube by the injector hold down clamp and retaining bolt.
The clamp load provided by this hold down crab and bolt works with the C-E Ring located at the injector nozzle to provide a compression seal with the injector hole tube inner surface. The high-pressure injector fuel line fittings are held in position to the tube by retaining nuts on each end (Refer to page 44). These retaining nuts have reverse threads, which requires a special tool for installation. At the inlet of the injector, recessed in the arm, is an inlet filter screen. This screen is a safety element intended to trap foreign material, which could find its way to the injector.
The injector assembly has three O-ring seals between the injector body and the cylinder head to control the flow of the return fuel from the injector into the cylinder head return passage (Refer to page 31). Unused fuel from the injector exits the injector through the passage between the second and third O- ring land into the return port in the cylinder head. The return fuel then passes through the external return fuel line from the cylinder head to the return fuel rail back to the fuel tank. Cylinder Head View VALVE OPERATING MECHANISM ELECTRONIC UNIT INJECTOR DDEC WIRING HARNESS TO INJECTOR HIGH-PRESSURE FUEL LINE TO INJECTOR RETURN FUEL LINE Fig.
7 Injector Installation in Cylinder Head Page 7