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 V8 DFI engines.

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

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 micrometer. Fuel is distributed via a central high pressure rail with separate lines leading to the fuel injectors.