Once the electronic-controlled engine failure, regular will be replace the nozzle and fuel metering unit. The fuel metering unit often binding causing vehicles due to the body wear rail pressure is difficult to establish, often can appear to start difficult, intermittent stall, fault phenomenon such as speed limit at 1500 RPM.

Low video: Bosch common rail system - fuel metering unit structure and fault analysis

First of all, we can be a video to the structure of fuel metering unit and fault for a simple understanding.

http://v.youku.com/v_show/id_XNTkzNjUyNTI4.html

We can see from the video fuel metering unit common damage often is caused by low quality or inferior fuel filter.
The working principle of low fuel metering unit
The fuel metering unit exactly is what to do? BOSCH, for example, the fuel metering unit, also known as the oil metering proportional valve. It is installed on high pressure oil pump inlet location, to adjust the fuel supply and fuel pressure value, controlled by the ECU computer.
As shown, proportion of fuel metering valve in the control loop have no electricity, the proportion of fuel metering valve is conduction, which is what we call the often open the electromagnetic valve, can to provide maximum flow of fuel oil pump. ECU by pulse signal changing high pressure oil pump inlet area and increase/decrease of oil.

Here we can simple understand fuel metering unit as an electromagnetic switch, its lead to the oil pump is controlled by conduction. Not power on when the switch is open, for the largest volume of oil pump, on the contrary, the current electromagnetic valve in zero position, oil the oil to the oil pump should be zero.
The fuel metering unit belong to precision components. If the improper maintenance or use inferior filter, often lead to fuel moisture or impurity causing too much fuel metering valve core wear or binding, leading to the engine won't work.

Low simple fault case analysis

Such as electronic control common rail engine downhill braking process, a chance to enter deceleration oil cut-off mode, namely will cut off the fuel injector fuel injection, at this time into the fuel metering solenoid valve should be completely closed, in order to prevent the fuel rail pressure continued to rise. But if metering unit binding condition exists and cannot be completely shut down will lead to rail pressure continued to rise, resulting in the common rail high drain valve (pressure limiting valve) will be forcibly push aside, the hands back line significantly high temperature, the engine will enter a state of emergency protection operation, the engine power speed will be limited.

Low editorial

It should be pointed out that, normal and effective work of the electronic control system and the scientific and reasonable maintenance is inseparable. General integration is installed on the oil pump fuel metering unit, not allowed to disassemble. Another different electronic control system of the fuel metering unit vary, such as Bosch, denso and Delphi each are not identical, electric control system of concrete need specific address.