Hi Tony

>>>Hi Dave. I don't know if This System is Different, But The Bosch Systems on most popular cars works the Opposite way to what you Describe, i.E No current flow = no pressure, full current = full pressure, i would expect this to be the norm ( fail safe ) as otherwise if the system got a bad connection, the pressure could go sky high. ??<<<

Yes the inlet metering valve on the Delphi system that most Fords have, works in quite the opposite way to the Rail Pressure Solenoid that you mention. The second example in my post, refers to the Bosch type that you are commenting on.

I agree that it sounds odd that a circuit failure on an inlet metering valve will drive it to full system pressure, but trust me it does! (hardly fail safe hey ) But in reality the PCM will see any excessive pressure & respond, by closing the inlet metering valve (by powering it up)

To clarify....

Delphi Inlet Metering Valve with full current applied = no fuel flow.

Bosch Rail Pressure Regulator (DRV) with full current applied = max fuel pressure.

The simplest way to confirm these strategies is to quite simply unplug the valve in question, (with engine idling) whilst scoping the rail pressure sensor & observe the response. If you unplug the inlet metering valve (Delphi system) with the engine at idle, the rail pressure goes sky high.


As a side note. On the Delphi system that Ford employ, when the engine is turned off, the inlet metering valve is energised fully, to strangle the fuel supply to the high pressure pump, then the injectors are fired rapidly to "vent" the fuel pressure away. This is the high pitched buzzing or whining noise that can be heard when you switch a Mondeo TDCI off.

Cheers

Dave