Fuel Supply, Low-Pressure Side
Fuel Supply, Low-pressure Side
Fuel quality
The engines are designed for unleaded premium fuel 93 octane(R+M/2). If fuel with a lower number is used, corresponding adaptation is performed by the knock control.
Fuel tank
Depending on the engine variant, a fuel tank with a filling capacity of 22.4 gal. (85 l) or 26.4 gal. (100 l) is installed. The tank bladder is identical. In the fuel tank with a filling capacity of 22.4 gal. (85 l), the roll-over valve is positioned lower down in the fuel tank by way of an adapter, with the result that the fuel nozzle is then switched off earlier.
- Cayenne V6/Cayenne S - filling quantity 22.4 gal. (85 l), reserve 3.9 gal. (15 l)
- Cayenne Turbo - filling quantity 26.4 gal. (100 l), reserve 3.9 gal. (15 l) (option for V6/S)
The active carbon filter is located behind the wheel housing liner of the right rear wheel. On USA vehicles, a leak detection pump (LDP) is used for the tank leakage test, as previously in the Cayenne vehicles. This pump is installed directly at the fresh-air connection of the active carbon filter.
ReturnLess Fuel System - RLFS
The low-pressure side of the fuel supply system consists of a returnless fuel system (RLFS - ReturnLess Fuel System). The speed-regulated 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 pressure of approx. 82 psi (5.7 bar). The sucking jet pumps in the fuel tank are also operated with the low-pressure side. The 2 fuel-level sensors are installed in the fuel tank for measurement of the fuel level.
1 demand-controlled electric fuel pump as well as the fuel filter (lifetime filter) and the fuel-pressure regulator (rel. fuel pressure approx. 82 psi/5.7 bar) are located in the fuel tank.
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 (top figure: access via the wheel housing liner at the rear right). The control unit for the electric fuel pump is used for stepless demand-based control of the fuel delivery rate. This control unit receives the setpoint speed of the fuel pump from the DME control unit via a bidirectional PWM interface and sends back diagnostic information.
Power supply
- The control unit is supplied with power via the main relay.
- Terminal 31 represents the connection to vehicle ground.
- Control by the DME control unit takes place via a bidirectional PWM interface.
Electric fuel pump
NOTE: The electric fuel pump must be operated only with the electric control unit.
The delivery rate is regulated by the speed of the electric fuel pump by way of the specified frequency (with limitation of the phase current).
Control
NOTE: Further 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 bidirectional PWM interface is also used for diagnosis of the control unit for the electric fuel pump. The speed of the electric fuel pump is regulated by means 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 brush-less three-phase synchronous motor.
Via the door contact
Cayenne V8: After the DME control unit switches to Sleep mode, it is woken again via a CAN wakeup signal when the driver's door is opened. The electric fuel pump is then operated with a significantly reduced speed for a period of 2 seconds. The electric fuel pump cannot be activated as long as the DME is now active (without ignition on). After the DME has switched back to Sleep mode again, this process can take place a maximum of three times without the ignition being switched on. This limit is designed to protect the vehicle electrical system management. Door contact activation can be activated again for a further three times with ignition On/Off.
When ignition is switched on
Cayenne V8: In contrast to door contact activation, the electric fuel pump is activated at maximum speed for 1 second after ignition on. This ensures rapid pressure build-up for a possible fast start-off.
Note on Cayenne V6
On these vehicles and depending on the fuel requirement, the delivery rate can be reduced to such an extent that the fuel pressure falls from approx. 82 psi (5.7 bar) to 58 psi (4 bar).
Internal design of the fuel tank RLFS
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.
- The safety instructions in the PIWIS information system must be observed when working on the fuel system.
Fuel tank ventilation
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. The tank vent valve is located in the engine compartment (on the right next to the electronic throttle in V8 engines).
When the engine is running, the fuel tank is vented by the tank vent valve, which is controlled by the DME control unit, to the intake system of the engine.
- On the turbo engine, a check valve closes the connection to the intake manifold when boost pressure is present.
Leak detection pump (LDP), for USA vehicles only
The functional principle for tank leakage diagnosis (LDP) is identical to that of the previous Cayenne vehicles. The complete fuel tank system is checked for possible leaks using the positive pressure method. This takes place only when the engine is running. The LDP is an electro-pneumatic diaphragm pump which is supplied with a vacuum. Evaluation by means of a reed contact switch located on the diaphragm takes place after the pumping phase.
Crankcase ventilation
Crankcase ventilation also takes place into the intake system.
- On the naturally aspirated engine, this takes place on the left of the electronic throttle directly into the intake manifold (and on the turbo engine if no boost pressure is present).
- On the turbo engine with boost pressure, ventilation takes place to the intake side of the left turbocharger.
The entry point directly on the intake manifold has an electric heater to prevent freezing at corresponding temperatures and to therefore avoid the risk of excess pressure in the crankcase.