W166 fuel pressure

[Samwalker]

2012 ml350 blutec
Keep getting the engine warning light on and downrating, when plugged in it’s throwing the fault
(Fuel pump pressure, too big difference between actual and target value.)
Swapped the fuel pressure sensor in the fuel line and this hasn’t cured it, the fuel pressure seems to stay at 9.15 bar even with the sensor unplugged, any ideas
Thanks Sam

 

[mersum1es]

What device you use reading pressure values (Are you sure it is capable of doing that....)? You are right, unplugging the valve should change value but it should give some 'crazy' value.

Usually fuel pressure problems in diesel engines are not sensor problem but either leak or control valve malfunctions. fuel quantity valve next to hp pump is very common culprit. On the other hand if injector tank line leak is too much, system cannot maintain required pressure.