Fuel presupply presupply control

Fuel presupply presupply control

The fuel supply on the 6-cylinder diesel engine M57TU2 in the E70 is ensured by a pressure-controlled system.

Brief description of components

The following components are described for the presupply system:

DDE control unit

The function of the fuel presupply control is integrated in the DDE control unit. The DDE uses the fuel pressure-temperature sensor to determine the current actual pressure in the presupply system. The DDE uses a number of input variables to determine the adjusting value signal factor to regulate the pre-delivery pressure. The pre-delivery pressure is regulated to a pressure of 4.8 - 5.0 bar.

The input variables relevant to determining the adjusting value are:

• Actual pressure in the presupply system
  
• Engine speed
  
• Injection volume
  

The adjusting value is sent to the fuel pump control in the form of a CAN message.

Fuel pressure / temperature sensor

The fuel pressure / temperature sensor measures the current actual pressure in the presupply system and sends the signal to the DDE control unit. For other functions in the DDE, the fuel pressure-temperature sensor also measures the fuel temperature.

Fuel pump control

The fuel pump control receives the adjusting value of the regulating circuit from the DDE as a CAN message. The value of the CAN message is converted via a characteristic curve into a voltage in the fuel pump control. This voltage is used by the fuel pump control to activate the electric fuel pump.

Fuel filter heating

If required, the fuel filter is heated with an electrical heating element. The DDE switches the fuel filter heating on and off with the signal S_KSH. The fuel filter heating is switched on under the following conditions:

• The electrical power output of the fuel pump is higher than the stored adaptation value ”electric fuel pump” plus an offset for more than 3 s. The offset is determined from a characteristic map and depends on the engine speed and fuel injection rate.
  and
  
• Fuel temperature < -1 °C
  AND
  
• Battery voltage > 9 V
  

The fuel filter heating is switched off again under the following conditions:

• Activation time > 5 min
  or
  
• Fuel temperature > 8 °C
  OR
  
• Battery voltage for more than 30 s < 9 V
  

Electrical fuel pump

The electric fuel pump is activated by the fuel pump control with a voltage of 6.5 - 15 V.

Notes for Service department

Diagnosis instructions

The control of the pre-delivery pressure is monitored by the DDE. Faults that occur due to control deviations are stored in the fault code memory of the DDE.

Activation of the electrical fuel pump is monitored by the fuel pump control. Faults that occur here are stored in the fault code memory of the fuel pump control.

When terminal 15 is switched on, the electric fuel pump is not activated. The electric fuel pump is only activated on actuating the starter motor.