Fuel system - Service procedures

Injectors, replacement

Special tool:6643, 981 2546

1

Drain the coolant.

2

Clean around the injectors, and at the pressure pipe and fuel return pipe connections.

3

Remove all pressure pipes. Remove the fuel return pipe at the injectors. Fit protection caps.

4

Unscrew the injectors’ yoke.

5

Turn the injector with a wrench and pull upwards at the same time. If the injector is stuck, use extractor 6643.

7

Fit

8

Fit

9

Fill

10

Recheck water level.

Recommendations for adjusting opening pressure, setting pressure and changing injectors

6

Clean

The injection process is carried out under very high pressure so that the dispersal of fuel is as effective as possible. As the injectors become older, opening pressure drops below the given pressure of new injectors. This pressure drop is completely normal and does not affect the function of the injectors or the engine performance to any great degree. Adjusting the injectors can mean that the service life of the nozzle assembly is shortened.

In the following we give some general recommendations on how to check the injectors and so avoid unnecessary replacing and adjusting of same.

The injectors should not be checked unless there are clear indications that they are not operating normally, for example, a considerable increase in exhaust smoke has been noted.

Most important in this test are the opening/adjusting pressures and leakage.

Spray pattern and chatter are more difficult to assess and do not give any clear indication of the condition of the nozzle.

In addition to the opening pressure, the “Technical Data” also state the setting pressure. This value refer to new injectors or injectors with new thrust spring. Since the setting pressure for a new spring is somewhat higher than the opening pressure, this gives one a certain margin to allow for fatigue of the thrust spring. When a thrust spring has become fatigued, the opening pressure drops about 5 percent.

Opening pressure will in time drop even more, but the injector will still function satisfactorily.

Investigations have shown that for a used spring the pressure drop evens out at about 15 per cent below opening pressure. However this pressure drop is no reason to adjust or replace the injector. The pressure drop lies within the specified working area.

Leakage test

The test is to check if there is any leakage from the nozzle. If leakage is present it occurs between the tip of the nozzle needle and the tapered sealing area of the nozzle sleeve.

Wipe the nozzle tip dry. Connect a pressure gauge and pump up pressure to 2 MPa (290 lbf/in2) below the opening pressure of the injector. Keep the pressure constant for 10 seconds. No fuel should drip from the nozzle tip, but a moist nozzle is acceptable.

Spray pattern

The condition of the nozzle is difficult to assess concerning spray pattern.

Many times the nozzle can function satisfactorily in the engine, even though some doubts may exist concerning spray pattern.