Fuel Pump Control Unit: Description and Operation

Fuel Supply

The engine is designed to provide optimum performance and fuel consumption if unleaded unleaded fuel 93 octane ((R+M)/2). When fuel with 90 octane ((R+M)/2) is used, the engine's knock controller automatically adapts the ignition timing. The fuel tank's filling capacity is approx. 16.9 gal. (64 liters), including approx. 2.6 gal. (10 liters) reserve capacity. The filling capacity is 17.7 gal. (67 liters) for the Carrera 4.

Fuel low-pressure system in DFI flat-six engines

- The low-pressure system delivers the fuel from the fuel tank to the high-pressure pump on the left cylinder head
- The new Carrera DFI vehicles also feature a returnless fuel system (RF)
- The demand-control function of the fuel delivery rate reduces fuel heating in the tank (low-pressure system). A control unit adapts the voltage at the fuel pump.

NOTE: The procedure for checking the fuel pressure and delivery rate of the fuel pump is described in the Technical Manual.

Functional diagram of the low-pressure side in the fuel tank

911 Carrera (997)







Design of the 911 Carrera 4 (997) fuel supply system

On Carrera 4 vehicles the fuel is transported into the pump chamber of the fuel pump by the sucking jet pumps (1A), which are located in the low-lying tank pockets on the left and right.







Fuel pressure on the low-pressure side

The fuel pressure on the low-pressure side is kept at a constant value of 5.0 bar by the pressure regulator in the fuel tank (previous MPI systems: approx. 4 bar). Electronic pilot control of the delivery rate can cause the fuel pressure to deviate slightly for a brief period, e.g. during extreme load changes when the vehicle is driven. To prevent the formation of vapour bubbles in the fuel supply system, the sustained pressure should not fall below 4.0 bar within 20 minutes of the engine being shut off.

Fuel pump control unit







The fuel pump control unit controls the voltage at the electric fuel pump in order to adapt the delivery rate of the fuel pump to the engine fuel requirement. This is performed via the control unit installed on the right-hand side of the plenum panel. The control unit is activated by a PWM signal from the DME control unit. The linear control range of the PWM signal has a pulse/duty factor of approx. 60% - 90%. The voltage control varies the current draw of the pump in the range between approx. 6 and 14 amperes.

The following control criteria are stored in the DME control unit:

- The fuel pump runs for approx. 3 seconds when the ignition is switched on
- When the engine is started and depending on the engine-start temperature, activation takes place for approx. 5 seconds at high voltage to achieve the maximum delivery rate
- Afterwards, activation depends on the engine's fuel consumption. At idle speed, the fuel pump is activated with minimal voltage (>8 V). Depending on fuel consumption, activation is steplessly increased up to the maximum delivery rate of the electric fuel pump