Injection Nozzle Test
The nozzle is - also for Common Rail and pump injectors - an important component for a well-functioning combustion. A defect is indicated by problems with starting the engine, excessive exhaust gas
pollutants, higher mileage and perhaps soot formation particularly with higher load. However, in comparison to the petrol engine a diesel engine quits much later in case of defects, i.e. it still runs
with errors a petrol car had given in already.
A dismounted injector body is submitted after a visual examination of heat effects and/or mechanical wear to a cleaning with ultrasound. Afterwards, it can be screwed on a pipe (figure on top) and
pressure tested by hand lever. While depressing the hand lever you should at the same time watch the opening pressure and the corresponding rattling sound. In case of a wrong opening pressure
the injector body should be opened and the preliminary tension of the spring should be changed. The steady sharp rays for hole-type nozzles out of every hose hole or the fine distribution for throttle pintle nozzles are important, too.
In any case, accident prevention regulations must be followed, because improper performed checks can lead to considerable skin injuries among other things. The leak test, by the way, is
performed with approx. 20 bar less than the nozzle opening pressure (do not confuse with the injection pressure).
However, how to handle injectors or elements of the pump nozzle. Actually, similar checks would be possible, as the lower part of the CR and pump nozzle consist of similar hole-type nozzles.
You would have to clear the way for CR systems electrically, though. With pump nozzles the matter is even more difficult because the high pressure develops in the element. The first way out of this
dilemma is displayed above in figure 2 on top, though, surely complicated. Here the high-pressure pump with the injectors is driven by a pump test bench, indeed, not so much to get spray pattern
pictures but more for a general examination. It is at least possible for CR, even if very extravagantly and, considering the costs for such a test bench, also expensive.
The problem today is nowadays solved by the electronic equipment. It can measure the contribution of every injection process to the rev stabilisation. With it a defective injection element can be
determined. Then, however, unfortunately, it is exchanged completely (see figure 3). There is no possibility for repairing.