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Basic Operation of Common Rail High-Pressure Pumps

Posted on 3/17/2016 2:59:26 PM

There is a big difference between the high-pressure Common Rail fuel injection system (HPCR) used in the GM and Dodge heavy duty pickups since the early 2000s and previously used pumpline-nozzle (PLN) systems.

In the PLN system a distributor or inline injection pump performs these critical functions: delivery of a pressurized and metered quantity of fuel to the injectors once for each power stroke, control of fuel injection timing, governor control of engine speeds and fuel delivery quantity related to the engine operating conditions.
 
While in the other hand,the engine or power train control module (ECM or PCM) in the HPCR system doing the function of  fuel metering, injection timing,rail pressure and engine speed control .
 
In order to supply a constant flow of fuel of sufficient volume and high-pressure to support the engine operating requirements,the high-pressure pump perform its basic function.The low-pressure gear pump, inlet-metering valve and high-pressure pumping elements make up of the  primary parts of the Duramax and Dodge high-pressure pumps.The low-pressure gear pump draws fuel from the tank and pressurizes the fuel to around 6 bar. The PCM controlled inlet-metering valve commonly referred to as the fuel control actuator or fuel rail pressure regulator controls the amount of supply pressure to the high-pressure pumping elements, thereby regulating the volume and high-pressure output of the high-pressure pump. The rail pressure is approximately 345 bar at idle and can reach 1,800 bar under full load conditions. The fuel flows from the high-pressure pump to the rail where  it is accumulated prior to flowing to the injectors.Later engine models include a pressure-control valve on the rail that works in conjunction with the inlet metering valve to provide improved rail pressure control.
 
Troubleshooting the Common Rail High-Pressure Pump
Because of the starting and low power conditions,it will bring problems of high-pressure pump.Before replacing the pump, check for diagnostic trouble codes (DTC), check the fuel supply system, measure the return fuel from the injectors and rail pressure limiting valve and monitor the desired vs. actual rail pressure values.
 
If the fuel supply system is good, a quick test of the pump can be done. Remove the high-pressure discharge line from the pump, attach a hose to the line and crank the engine over until fuel is discharged from the hose. Now collect and measure the fuel discharge by cranking the engine for 10 seconds three times. If the cranking speed is around 150 RPM the collected amount should be 70 ml and at 200 RPM it should be around 90 ml. If the discharge volume is low, suspect a bad high-pressure pump.


Common Rail High-Pressure Pumps

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