Fuel, Exhaust & Engine Electrics
Page 2.16
Cayenne V8 Naturally Aspirated Engine
The high pressure pump used in the Cayenne S is a three-piston pump
with a maximum delivery rate of approx. 47.5 gals./180 liters/h at
1740 psi (120 bar). It builds up pressure and ensures flow control. The
following components are integrated into the high pressure pump: Flow
control valve with pressure reducing function for the fuel high pressure
side, pressure control valve, bypass valve, a temperature compensator
on the oil side and a fuel strainer on the inlet side with a mesh width of
approx. 50 µm. Fuel is distributed via a central high pressure rail with
separate lines leading to the fuel injectors.
Cayenne Turbo
The high pressure pump -HD- used in the Cayenne Turbo is a six-piston
pump with a maximum delivery rate of approx. 58 gals./245 liters/h at
1740 psi (120 bar). It builds up pressure and ensures flow control.
The following components are integrated into the high pressure
pump:
Flow control valve -1- with pressure reducing function for the fuel high
pressure side, pressure control valve, bypass valve, two temperature
compensators on the oil side -2- and a fuel strainer on the inlet side
with a mesh width of approx. 50 µm. Fuel is distributed in the same way
as for the V8 naturally aspirated engine via a central high pressure rail
with separate lines leading to the fuel injectors.
Flow Control Valve For Fuel High Pressure
The electric control valve for the fuel high pressure side -1- is located
on the fuel high pressure pump and operates as a flow control valve.
The Motronic control unit regulates the delivery rate of the high pressure
pump in the fuel supply to the pump via the control valve. When the
engine is switched off, the fuel high pressure is reduced by an inte-
grated pressure reducing valve. The fuel pressure sensor monitors the
required fuel pressure (approx. 580 psi/40 to 1740psi/120 bar).
• 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). In this case, the bypass valve
in the pump opens and provides a direct route from the low pressure
side to the high pressure side.
• The bypass valve is also activated for filling the empty fuel rail on new
engines or following repairs in order to reduce starting times.
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