Fuel Supply, Low-Pressure Side
Fuel Supply, Low-pressure Side
Fuel quality
The engines are designed for unleaded premium fuel 93 octane ( R+M2 ). If fuel with a lower number is used, corresponding adaptation is performed by the knock control.
Fuel tank
The fuel tank has a filling capacity of 22.4 gal. (85 l), reserve 3.4 gal. (13 l) or optional 26.4 gal. (100 l).
ReturnLess Fuel System - RLFS
Consisting of:
- 1 demand-controlled electric fuel pump
- Fuel filter (lifetime filter in the tank)
- Fuel-pressure regulator (fuel pressure approx. 83 psi/5.7 bar max.)
The low-pressure side of the fuel supply system consists of a returnless fuel system (RLFS - ReturnLess Fuel System). The variable-speed electric fuel pump delivers the fuel via the fuel filter and fuel-pressure regulator (in the fuel tank) to the quantity control valve on the high-pressure pump with a max. pressure of approx. 83 psi (5.7 bar). The sucking jet pumps in the fuel tank are also operated with the low-pressure side.
The two fuel-level sensors are installed in the fuel tank for measurement of the fuel level.
Control unit for electric fuel pump
Operating principle
The control unit of the electric fuel pump is installed at the rear above the right side of the fuel tank (access via the wheel housing liner at the rear right). It is used for stepless control of the electric fuel pump. This control unit receives the setpoint speed for the fuel pump from the DME control unit via a bidirectional PWM interface and feeds back diagnosis information.
Power supply
The control unit has a power supply with +.
Terminal 31 represents the connection to vehicle ground.
Control input
NOTE: Diagnostic information on the PWM signal and diagnosis is described in Guided Fault Finding.
The output of the fuel pump is controlled by the DME control unit by a PWM control signal. This bi-directional PWM interface is also used for diagnosis of the control unit for the electric fuel pump.
Electric fuel pump
The speed of the electric fuel pump is regulated by way of the specified frequency within the power limits of the fuel pump (with limitation of the phase current) and independently of the vehicle electrical system voltage (voltage compensation). The pump motor is a 3-phase synchronous motor without position feedback and without sensor.
Note on the control unit for electrical fuel pump on the Cayenne
On the Cayenne S Hybrid, the fuel pump delivery rate can be reduced to such an extent that the fuel pressure falls from approx. 83 psi (5.7 bar) to below 58 psi (4 bar), depending on the fuel requirement. The low pressure is detected by a pressure sensor for this. The fuel pressure sensor for detecting the low pressure is installed in the high-pressure pump supply line.
This control function differs from the V8 engines, which have a constant fuel low pressure of approx. 83 psi (5.7 bar).
Internal design of the fuel tank
NOTE: The procedures for checking the fuel pressure, holding pressure and delivery rate of the electric fuel pump are described in the PIWIS information system. Observe the relevant safety instructions when working on the fuel system.
Tank ventilation
The fuel tank is aerated and vented exclusively via the active carbon filter, which acts as an intermediate storage device for any HC emissions. Regeneration of the active carbon filter takes place via the tank vent valve when the engine is running. The active carbon filter is installed behind the wheel housing liner at the rear right. When the engine is running, the system is vented via the electric tank vent valve (in the engine compartment) to the intake system of the engine.
Leakage diagnosis pump (LDP):
On USA vehicles, a diagnosis module for tank leaks (DMTL) is used for the tank leakage test, as in the current sports cars. This module is installed directly at the fresh-air connection of the activated carbon filter.
The function of the diagnosis module for tank leaks corresponds to that of the modules installed in the 9X7 vehicles. A function description can be found in the corresponding Introbook, in the PIWIS information system.