Fuel Supply
Fuel Supply
The engine is designed to provide optimum performance and fuel consumption if unleaded premium fuel with 93 octane ((R+M)/2) is used. If unleaded premium fuels with a lower octane number is used, the engine's knock controller automatically adapts the ignition timing. The maximum filling approx. 26 Gals. (100 liters), with a reserve of approx. 3 Gals. (12 liters).
SAFETY: Always read and follow the safety instructions in the Technical Data, when working on the fuel supply system.
- Fuel low-pressure system in DFI engines.
TECHNICAL MANUAL: The procedure for checking the fuel pressure and the amount of fuel delivered by the fuel pumps is described in the Technical Data.
- The low pressure system delivers the fuel from the fuel tank to the high pressure pump on the cylinder head.
- The new Cayenne vehicles have a returnless fuel system (RF).
- The demand control function of the fuel delivery rate reduces fuel heating in the tank by switching on the second fuel pump.
The fuel tank is not symmetrical. The left half of the tank has a higher volume than the right side. There is a "hump" in the middle so that both chambers are separated from each other once a certain fuel level is reached in the tank. When the tank is half full, the left fuel pump is activated because the left half of the tank has the higher volume. The fuel pumps are each supplied by one sucking jet pump whose hoses are routed diagonally and which "helps itself" to fuel from the other half of the tank.
The fuel pressure and the way in which the two fuel pumps are activated has changed compared to Cayenne vehicles up to model year 2006. On Cayenne vehicles up to M.Y. 2006, the left fuel pump was permanently activated and the right pump was only activated as required (for starting, higher delivery rate, etc.).
Functional diagram of the low pressure side in the fuel tank.
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 engines.
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.
Flow Control Valve For Fuel High Pressure
The control valve for fuel high pressure located underneath the fuel high pressure pump operates as a flow control valve. The Motronic control unit maintains the fuel high pressure going to the fuel rails of cylinder bank 1 and 2 at a pressure of between 508 psi (35 bar) and 1450 psi (100 bar) via the control valve. 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).
Fuel Pressure Sensor
The fuel pressure sensor is installed on the lower fuel rail (cylinder bank 2) and informs the Motronic control unit about the current pressure in the fuel high pressure system. The Motronic control unit evaluates the signal and regulates the fuel high pressure via the fuel pressure control valve in the high pressure pump. If the fuel pressure sensor fails, the fuel pressure control valve is activated with a fixed value by the engine control unit.
Pressure Control Valve
The pressure control valve is located on the fuel rail of cylinder bank 1. The valve opens a connection to the fuel low pressure system if the fuel pressure in the high pressure system exceeds 1740 psi (120 bar).
Two High Pressure Rails
Two high pressure rails are used in the V6 engine. The fuel is pumped from the high pressure pump to the two distribution rails on cylinder bank 1 and 2 via the high pressure line. The same fuel pressure is available for all fuel injectors from there.
Fuel Injectors/High Pressure Injectors
The electromagnetically operated fuel injectors are located in the cylinder head. They are activated by the Motronic control unit in accordance with the firing order. Following activation, they inject fuel directly into the combustion chamber at a pressure of 580 psi (40 bar) to 1740 (120 bar). The injectors for both cylinder banks are on the intake side of the cylinder head. This arrangement allows the injectors for cylinders 1, 3 and 5 to run through the inlet port on the cylinder head. The injectors for cylinder bank 1 are therefore longer than the injectors for cylinder bank 2.
Since the injectors are inserted from the same side for both cylinder banks, the piston recesses of cylinder bank 1 and 2 must be molded differently so that the injected fuel is whirled around and mixed perfectly with the air that is drawn in. This is necessary because the fuel injectors and intake valves on both cylinder banks are arranged in different angles.
In addition to the amount of fuel injected and the injection time, the shape and alignment of the fuel jet is also important here. A defective injector is detected by the misfire detection system and is not activated again.