Poacher turned Gamekeeper
Join Date: Oct 2007
Location: Staines, Middlesex.
Car: MG ZT-T CDTi.
Hi pressure pump regulation is controlled by a solenoid in the back of the pump. The ECU senses the fuel rail pressure, by means of the fuel rail pressure sensor, the ECU then sends a pulse width modulated signal to the fuel pressure regualtion solenoid. This then allows the ECU to keep the fuel rail pressure between it's upper & lower limits.
The fuel pressure upper & lower limits are determined by the ECU, dependent on many factors, i.e. pedal demand, engine revs, etc.
It is not very easy to test the fuel pressure regulator in it's own right, but the use of actual values on a decent scan tool will at least give you two important pieces of live data, these being ACTUAL FUEL RAIL PRESSURE & NOMINAL FUEL RAIL PRESSURE.
From these two it can be seen whether the ECU is able to regulate the pressure dependent upon demand.
If it needs further investigation, then a test kit would be required to test the regulated & unregulated output of the HP pump.
You would really need to get the car to a diesel specialist if these tests need doing.
HTH, regards, Rob.
P.S. you need to take a bit of care, don't crack the HP system down for some while after running, the HP side can run in excess of 2000BAR, which is around 29,000PSI in old money, so can do you some damage.