Siemens-Common Rail System – Fuel filter

Fuel filter of the 1.4L Duratorq-TDCi (DV) diesel engine

1 Fuel feed port (from fuel tank)
2 Fuel feed port (to high pressure pump)
3 Fuel filter with water separator
4 Water drain screw
5 Electric fuel pre-heater

Different fuel filters are used for the Siemens common rail System depending on the type of engine. Their operating principles and service-relevant characteristics, however, are very similar. Both fuel filters are equipped with a water separator, which must be drained regularly in accordance with the specified service intervals.

For this purpose, open the water drain screw on the filter housing and allow approx. 80 to 100 ml of liquid to drain into an appropriate container. Then tightly close the water drain screw again and dispose of the liquid. Both fuel filters also featured a fuel heater, which is activated at low temperatures.

Fuel filter of the 2.0L Duratorq-TDCi (DW) diesel engine

1 Fuel feed port (from fuel tank)
2 Fuel feed port (to high pressure pump)
3 Electric fuel pre-heater
4 Water drain screw

Fuel pre-heating is controlled by a bi-metallic strip and functions independently of the PCM. The bi-metallic strip controlled fuel pre-heater is activated when the ignition is on (ignition key in position II) regardless of whether the engine is running or not.

Regardless of the ambient temperature, the bi-metallic strip closes the circuit and the heating element in the fuel pre-heater is activated.

• In the 1.4L Duratorq-TDCi the on/off temperature for the heating element is approximately 5°C.
• In the 2.0L Duratorq-TDCi (DW) diesel engine the heating element is switched on at –2°C ± 2°C and switched off at +3°C ± 2°C.

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.

Note: a certain quantity of air is drawn out of the fuel tank together with the fuel when the transfer pump draws fuel into the high-pressure pump. The air bubbles are very small, however, and cannot initially be seen with the naked eye. The air bubbles are separated out in the fuel filter and clump together to form larger bubbles. These air bubbles occasionally emerge from the filter material and are drawn into the high pressure pump. They can be seen through a transparent hose. This form of separation is entirely normal. The visual inspection for air bubbles in the transparent hose is therefore not counted as a fault diagnosis.

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. September 2018 by Ron
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