Caterpillar EMS Electronic Unit Injector

Both the 3100-3500 and C series engines employ EUIs that combine mechanical actuation with electronic control over fuel volume. Figure 6-15 illustrates an EUI in cross-section. A roller-tipped rocker arm, acting on in the injector plunger, provides the force necessary to generate the 28,000-psi injection pressure. The solenoid valve, shown on the left of the drawing, opens the spill/fill port to admit fuel into the injector barrel during the period of plunger retraction. A spring-loaded check valve, located near the injector tip and set to open at 5000 psi, remains closed during the fill process.