Diesel injectors

The injector is the component that introduces fuel into the combustion chamber. It is not enough for the fuel to enter: it must do so as very fine droplets, with the right spray shape and at the exact moment of the cycle. Complete combustion of the mixture with air depends on that atomization.

A small variation in delivery or spray shape already shows in fuel consumption, exhaust smoke, noise and engine power.

Mechanical injectors open by pressure: when fuel pressure exceeds the force of a calibrated spring, the needle lifts and fuel leaves through the nozzle holes. They are associated with rotary or in-line pump systems.

Electronic injectors are activated by a signal from the ECU. They may use a solenoid or a piezoelectric crystal to open the valve, and they allow the injection to be split into several phases per cycle. They operate at pressures far higher than mechanical ones and require even tighter tolerances.

Diagnosis is done on a test bench that reproduces working conditions. Delivery is measured at several load points, along with return flow (the fuel that goes back to the tank, which indicates internal leakage), the spray pattern and angle and, on electronic injectors, the electrical response of the actuator.

These measurements show whether the injector is clogged, dripping, internally worn or simply needs cleaning. In Common Rail systems the behavior of the injectors of the same engine is also compared, because the difference between cylinders matters as much as each individual value.

Ultrasonic cleaning immerses parts in a liquid vibrating at high frequency. The vibration creates microbubbles that collapse on the surface (cavitation) and remove carbon and varnish from hard to reach areas, such as the nozzle holes, without damaging the metal.

It is a useful stage within a repair, but it does not replace it: after cleaning, the injector is measured again to see whether it recovered its values or whether components need to be replaced.