Lets start at beginning, you must understand how the common rail system works, you have a Bosch edc 16 system, probably a CP3 pump with L/P pump on back of H/P pump. there are 3 basic pressures you should be looking for. 1 - LOW PRESSURE. Generated by L/P pump in tank / chassis,[app 1 bar] if there is a manual primer there's NO L/P pump in tank / chassis and the low pressure is generated by the L/P pump on back of H/P pump,[suction] try running a clear plastic pipe directly into clean container. 2 - TRANSFER PRESSURE. Generated by L/P pump to supply constant pressure [app 5 bar] to H/P pump controlled by mechanical T/P regulator on front of H/P pump. 3 - HIGH PRESSURE. Generated mechanically by pistons in H/P pump but controlled by 1 or 2 regulators. The 1st H/P reg fitted on the H/P pump controls the amount of fuel entering the H/P pump, the more fuel that enters the H/P pump the higher the pressure, BE CAREFULL,this reg can be + or - control, [+ disconnect = opens,no pressure] [- disconnect = closes,high pressure, won't start as the pressure will be too high] The 2nd H/P reg for more accurate H/P control is fitted on rail beside return pipe, observe the amount of fuel in return pipe [no fuel at start up] fuel only at high revs. GOOD LUCK. John.