Delphi-Common Rail System – Fuel filter

1 Connection – return pipe
2 Connection – feed pipe (from tank)
3 Connection – feed pipe (to the high-pressure pump) *
4 Filter element
5 Water drain screw
6 Bi-metal
7 Ball valve
* Feed pipe connections – in this diagram, shown directly behind one another.

The common rail injection system has a fuel filter which is matched to the specific requirements of the system.

The main new feature here is the fuel pre-heating function.

A temperature-dependent control valve is incorporated in the fuel return line in the fuel filter.

The control valve is a bi-metal-controlled ball valve. By heating the bi-metal, the ball valve is opened continuously.

At a temperature of < 0 °C the return flow rate to the filter is approximately 55 to a max. of 65 l/h. At a temperature of > 50 °C, the return flow rate to the filter is less than 5 l/h.

This type of fuel recirculation ensures that no back-pressure is generated in the fuel return system.

Draining the fuel filter
The fuel filter must be drained regularly at the prescribed maintenance intervals.
To drain the filter, loosen the drain screw and allow the fluid to escape until pure diesel fuel appears (use a hose and container to collect the fluid).
Note (depending on vehicle): Because access to the drain screw is restricted, it is first necessary to remove the fuel filter – refer to the current Service Literature.
Depending on the vehicle, the generator may also be located below the fuel filter; as a result, there is an increased risk of fire caused by fuel draining out of the drain screw.

Possible causes of faults
Fuel filter may be blocked by dirt. Air may also enter the low-pressure system as a result of leaks in the fuel filter.

Effects of faults
Poor engine starting when warm or cold
Irregular idling
Engine does not start.
Engine starts, but cuts out again immediately afterwards.
Engine has insufficient power.

02. August 2018 by Ron
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