Fuel Pump: Description and Operation

Fuel Pressure On The Low Pressure Side.

For DFI engines, the fuel pressure on the low pressure side has been increased to approx. 80 psi/5.5 bar (this was previously approx. 58 psi/4 bar). The left or right fuel pump is operated as the main pump in order to distribute the higher load to both fuel pumps, depending on the fuel level.

The fuel pumps are activated if the level of fuel in the tank is reduced and if the engine requires more fuel:
- Fuel level > 15.8 gal. (60 liters) to 26 gal. (100 liters): When the tank is relatively full, the right fuel pump is activated; if more fuel is required (> 13 gal./50 liters/h), the left pump is activated.
- Fuel level > 4 gals/15 liters to 15.8 gals/60 liters: When the tank is half-full, the left fuel pump is activated; if more fuel is required (> 13 gals/50 liters/h), the right pump is activated.
- Fuel level < 4 gals./15 liters: If the tank is relatively empty, both pumps run continuously.

Other switching functions include:
- If the ignition was switched off for more than 30 minutes, the left fuel pump is activated for approx. 1 to 2 seconds when the driver's door is first opened in order to build up fuel pressure even before the ignition is switched on.
- Both fuel pumps are activated while starting the engine and for several seconds after starting the engine.

Fuel High Pressure System in DFI Engines

The fuel high pressure system generates an injection pressure of up to 1740 psi (120 bar) in the combustion chamber. The components of the V6 engine and the V8 engines are different.

The following pages describe the functions of the components of the V6 DFI engine.

SAFETY: Always read and follow the safety instructions in the Technical Data, when working on the fuel supply system.

V6 DFI Engine

The fuel high pressure system in the V6 DFI engine is made up of the following parts/components.







Fuel High Pressure Pump







The fuel high pressure pump creates a high pressure of up to 1740 psi (120 bar), which is required for injection. It is controlled by demand and adapts the fuel quantity according to engine requirements via a flow control valve. This piston pump with one piston is located on the cylinder head. The high pressure pump is driven by the timing chain via a double-cam gear wheel. The double-cam gear wheel uses a roller to actuate the pump piston, which creates the fuel high pressure in the pump.

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 Data when securing all fuel lines in the high pressure area.


Fuel High Pressure Pump

The fuel high pressure pump pumps the amount of fuel required for injection and builds up a fuel pressure of up to 1740 psi (120 bar). The axial piston pump is driven by the inlet camshaft. The Cayenne S and Cayenne Turbo are equipped with different high pressure pumps.