BMW 3 Owners & Service Manuals

BMW 3: Fuel high-pressure pump

The single-piston high pressure pump by Bosch, well-known from the B46 engine, is used. The high pressure pump HDP6 is driven by a triple cam which is attached to the exhaust camshaft. To be able to accommodate a fuel system pressure of 350 bar (5076 psi), the pump piston and tappet have been modified.

Low pressure fuel is supplied to the high pressure pump via the in tank electric fuel pump.

Fuel preparation
Bosch high-pressure pump HDP6

  1. Low-pressure connection
  2. High-pressure connection
  1. Balancing chamber
  2. High-pressure non-return valve
  3. Pressure-limiting valve
  4. Pump piston
  5. Fuel fuel quantity control valve
  6. Electrical connection of fuel quantity control valve

The fuel quantity control valve at the high pressure pump adjusts the fuel pressure in the rail. The maximum pressure in the rail is 350 bar (5076 psi); it is kept throughout the engine's entire operating range. The fuel pressure is only reduced to 150 bar (2175 psi) during idling. The high pressure pump contains a pressure limiting valve which opens at a pressure of 400 bar (5801 psi). The fuel quantity control valve is activated via a Pulse-Width-Modulated (PWM) signal and assumes the open position in the de-energized state. This means the pump piston of the high pressure pump cannot compress the fuel.

The high pressure pump in the high-pressure fuel system cannot build up pressure if the fuel quantity control valve is pulled off. In this situation, the maximum low fuel pressure of 5.8 bar (84 psi) would be present in the rail during an engine start. The system would be in emergency operation. To ensure the engine remains capable of running in this state, the opening period of the solenoid valve injectors has been extended and the idle speed increased. Although the vehicle remains drivable, the maximum engine performance is not available.

Due to the high fuel pressures, the fuel lines must never be detached when the engine is in operation.

When removing the high pressure pump, follow the specifications in the current repair instructions.

Excessive tilting of the pump can damage the pump piston!

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