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Denso-Common Rail System – High pressure pump

The diagram shows the high pressure pump in the 2.4L Duratorq-TDCi

A High pressure fuel to fuel rail
B Fuel return
C Fuel feed
1 High-pressure chamber outlet valve
2 High-pressure chamber inlet valve
3 Pump plunger
4 Fuel metering valve return spring
5 Fuel metering valve
6 Pre-pressurize control valve (pump interior pressure)
7 Transfer pump (rotor pump)
8 Fuel inlet
9 Fuel filter
10 Eccentric cam ring
11 Eccentric cam
12 Drive shaft
13 Fuel tank
14 Overflow throttle valve


The high-pressure pump provides the interface between the low and the high pressure systems. Its function is to always provide sufficient compressed fuel under all operating conditions and for the entire service life of the vehicle.

Low-pressure zone:
• The transfer pump draws fuel out of the fuel tank via the fuel inlet.
• The pump internal pressure is adjusted via the admission-pressure control valve. This ensures that sufficient lubrication and cooling are always provided for the high pressure pump components.

Excess fuel is transferred to the inlet side of the transfer pump via the admission-pressure control valve.

• A portion of the fuel is transferred to the fuel metering valve from the transfer pump. The fuel quantity delivered to the high pressure chambers is determined by the opening cross-section of the fuel metering valve.

• The small restriction bore in the overflow throttle valve provides for automatic bleeding of the high pressure pump. The entire low-pressure system is designed to allow a defined quantity of fuel to flow back into the fuel tank via the overflow throttle valve. This assists cooling of the high pressure pump.

High-pressure zone:
– A total of two high pressure chambers, each with one pump plunger, are used for high pressure generation.
– The drive for the pump plungers is via an eccentric cam, which is in turn driven by the drive shaft (principle similar to the Bosch common rail system, see relevant section in this Student Information).
– The high pressure pump permanently generates the high system pressure for the fuel rail.

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