Fuel, Exhaust & Engine Electrics
Page 2.13
Note
Pressure variations can occur on the low pressure side while measuring
fuel pressure at idling speed due to the piston pump on the high
pressure side with one piston.
Technical Manual
Always read and observe the specifications in the Technical Manual
when securing all fuel lines in the high pressure area.
Flow Control Valve For Fuel High Pressure
The control valve for fuel high pressure located underneath the fuel high
pressure pump operates as a flow control valve. The Motronic control
unit maintains the fuel high pressure going to the fuel rails of cylinder
bank 1 and 2 at a pressure of between 508 psi (35 bar) and 1450 psi
(100 bar) via the control valve. If the control valve fails, the Motronic
control unit goes into emergency operation, whereby the engine can still
run in a limited way with low pressure (80 psi/5.5 bar).
Fuel Pressure Sensor
The fuel pressure sensor is installed on the lower fuel rail (cylinder bank
2) and informs the Motronic control unit about the current pressure in
the fuel high pressure system. The Motronic control unit evaluates the
signal and regulates the fuel high pressure via the fuel pressure control
valve in the high pressure pump. If the fuel pressure sensor fails, the
fuel pressure control valve is activated with a fixed value by the engine
control unit.
Pressure Control Valve
The pressure control valve is located on the fuel rail of cylinder bank 1.
The valve opens a connection to the fuel low pressure system if the fuel
pressure in the high pressure system exceeds 1740 psi (120 bar).
Two High Pressure Rails
Two high pressure rails are used in the V6 engine. The fuel is pumped
from the high pressure pump to the two distribution rails on cylinder
bank 1 and 2 via the high pressure line. The same fuel pressure is
available for all fuel injectors from there.
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