Fuel injectors (Mercedes-Benz Vito W639)

Purpose

The injectors are designed to inject atomized fuel into the combustion chamber with the most advantageous spray pattern.

Design

Accommodation

The injectors are located in the cylinder head and are connected to the high-pressure fuel manifold via high-pressure pipes.

Note: The spray spring (23) holds the needle (18) in the spray lock position when the pressure difference in the upper and lower chambers is no more than 40 bar (4 MPa).

2. There is no electrical power to the solenoid, there is high pressure, but no injection.

In this phase of the injector operation, pressure from the HPC is supplied through the feed channel to the lower chamber, and also through the throttle opening to the upper chamber. The fuel pressure in the upper and lower chambers is balanced. The spray needle return spring holds the needle in the spray valve closed position. There is no injection.

3. Start of injection (the solenoid valve is open, power is supplied to the injector).

When voltage is applied to the winding of the electromagnetic valve (6), the solenoid core (26) is drawn in, compressing the spring (33). At the same time, the ball valve (12) opens and the fuel from the upper chamber (39) flows through the throttle opening (37) of the pressure relief channel into the fuel return circuit. Pressure in the upper (balancing) the camera is lowered. The unbalanced fuel pressure in the lower chamber creates a force that lifts the needle.

4. Injection (the solenoid valve is open, power is supplied to the injector).

While the ball valve (12) is held open, the unbalanced pressure in the chamber (43) holds the spray needle (18) open. The pressure difference in the upper (39) and lower (43) chambers is ensured by the ratio of the flow capacity values of the throttle openings (36) and (37).

5. End of injection (solenoid valve closed).

When the electrical power is removed from the solenoid coil, the valve closes. In this case, the pressure in the upper chamber is restored to a value equal to the pressure in the lower chamber. The force of the return spring (23) closes the spray valve.

Functioning

1. There is no electrical power supplied to the solenoid, there is no injection.

The pressure in the high pressure feed channel (38) is approximately equal to atmospheric pressure. The ball valve (12) is locked by the force of the spring (33) acting on the core of the solenoid (26).

Removal and installation

1. Remove the clamp (6).

2. Remove the injectors (11). If the injectors cannot be removed, install the grip (7) in place of the clamp (6) and, using the impact puller (8) and (9), remove the injectors (11) together with the sealing ring.

3. Clean the nozzles and nozzle holes using brass brushes of suitable sizes, lubricate the nozzles with a special lubricant, blow out the holes and protect them from contamination by first inserting plugs.

Note: Removing injectors on engines 646.980 and 646.981 differs from that described above (for engines 646.982 and 646.983) the fact that instead of the grip (7) a threaded adapter (12) is used.

4. Install in reverse order. When installing nozzles, to prevent unnecessary stress in high-pressure pipelines, they should be installed (pipelines) on the injectors until the final tightening of the injector mounts,



5. Check the fuel system for leaks by briefly running the engine.

Tightening torques for threaded connections

Injector clamp mounting screw 7 Nm + 90°.