How Diesel Fuel Injectors Work

Diesel injectors have improved significantly over the years, but even though they have become increasingly more reliable, it’s still helpful to know how they work in conjunction with the entire common rail fuel system your machine uses in order to mitigate problems.

Diesel fuel from the injection pump will enter the mechanical injector body and start building pressure. Once the pressure is high enough (approx 4,000 psi), the check valve in the injector is opened off its seat, and fuel sprays through. Most engines use ECM’s to control and open the diesel injector nozzles. The nozzle attached to the injector sprays fuel directly into the air as soon as the valve opens. Any excess fuel that remains after the valve is opened is then returned back out through the injector body, then back to the injection pump.

All new injectors need to be coded into an Electronic Control Unit (ECU) machine for them to work properly. To code the injectors, you can use a Bobcat dealer or visit, and rent a remote programming kit. 

The ECU tells the injector when and how long to fire. The ECU sets off precise and pressurized spray into the combustion chamber through its nozzles, causing ignition. This process happens in milliseconds. 

A deeper look into the injector

Each fuel injector is different, but most have about 15 main parts which include the filter, guide ring, core spring, seat spring, seat, pole piece, stop, solenoid coil, solenoid body, core ring, core, spray tip, director and spray tip housing. As mentioned above, the fuel flow is controlled by the ECM by raising a ball off its seat. The fuel then flows through the seat orifice and out through a fixed director plate with several holes. The director plate directs the fuel spray pattern. These injectors typically have a 10 to 15 degree angle spray pattern. The fuel atomization of this type of injector is comparable to the disc type injector. Disc and ball type injectors tend to be less susceptible to clogging.

Do you have questions about diesel fuel injectors or other related parts? Contact our team at Expert Diesel Parts today or view the wide selection of diesel injectors that we carry for your engines.