Fuel is fed to the injector at a relatively low pressure (50-70 psi) and a solenoid controls the high-pressure oil going into the plunging mechanism to ramp injection pressure up to 21,000 psi.

One way to help take the load off a 6.6L Duramax LML engine’s high-pressure fuel pump—be it the stock CP4.2 or a CP3—is to install an aftermarket lift pump sourced from companies such as AirDog.