CDI fuel low pressure circuit, function - GF07.16-P-3001GZ

ENGINE 642 in MODEL 164.1 /8, 251.0 /1 

ENGINE 642 in MODEL 463.3 

ENGINE 642 in MODEL 461.3 

Shown except code (494) USA version 

Fig 1: Fuel Low Pressure Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Model 164, 251 

When starting the engine and after recognizing that the engine is running the CDI control unit (N3/9) controls the fuel pump using the integral fuel pump relay (F4kO) in the rear SAM control unit (N10/8), which pumps the fuel through the fuel main filter to the high-pressure pump.

Model 461 

When starting the engine and after recognizing that the engine is running the CDI control unit (N3/9) actuates the fuel pump via the fuel pump relay (K27) which delivers fuel via the fuel main filter to the high-pressure pump.

Model 463 

When starting the engine and after "engine running" has been recognized, the CDI control unit (N3/9) actuates the fuel pump via the fuel pump relay (N10/2kA) integrated in the rear signal acquisition and actuation module (SAM) (N10/2) which delivers the fuel over the fuel main filter to the high pressure pump.

The pressure of the pumped fuel is limited to approx. 4.0 to 4.5 bar via the pressure relief valve integrated in the high-pressure pump, the quantity control valve and the fuel temperature sensor. The quantity control valve also regulates the supply of fuel to the high-pressure pump, in order to increase engine efficiency and to keep the fuel temperature low. The leak fuel of the fuel injectors is led back before the main fuel filter into the system. The reduced fuel from the pressure regulator valve and the fuel which is not required is led back over the return line to the fuel tank.

For vehicles with code (494) USA version the fuel main filter is fitted with a fuel filter water level sensor (B76) in the fuel main filter for water level recognition.