Design and function
1.
The gear type feed pump is driven by the crankshaft via an intermediate gear. High pressure is needed in order to ensure that the unit injectors are filled. The flow must be sufficient to even out any temperature differences in the cylinder head fuel channel.
2.
The fuel filter housing features a built-in electric pump for venting the fuel system and draining water. A built-in check valve (2) in the pump prevents the fuel from flowing back when the engine is shut-down.
3.
The control module is screwed to the engine with four vibration absorbing rubber blocks and is cooled by fuel through a cooling coil fastened on the outside of the control module, before the suction side of the feed pump.
4.
The unit injectors are a combination of injection pump and injectors that works with much higher pressure than an ordinary injector. The opening pressure is about 320 bar (4,600 psi). The working pressure can be up to 2000 bar (29,000 psi).
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Injection timing and the amount of fuel to be sprayed is determined by the control module, which signals electromagnetic fuel valves built into the unit injector. The force on the unit injector is transferred via the rocker arm from a ridge on the camshaft. The unit injectors are made and classified by tolerance. Each unit injector is marked with a code on the top side of the electric connection. When replacing, the new codes shall be programmed. 5.
A hollow screw with an integrated bypass valve, which controls the feed pressure to the fuel system, is located in return line from the cylinder head. The opening pressure is 400-550 kPa (5880 psi). The high feed pressure is needed to ensure that the unit injectors are filled. The bypass valve also has an integrated vent valve that automatically vents the system, allowing a small volume of fuel back to the tank.
6.
Excess fuel from the bypass valve is mixed with fuel from the suction side in the manifold housing, and fed back to the feed pump.