[Engine] P1166 fault code and knocking sound

[Sahloul]

Hi

Bare with me, this is a long one...

I have an 04 Peugeot 2.0 hdi Siemens 90.

A while ago, car started making a knocking sound under hard acceleration and a cloud of white smoke in the morning.
I traced it down to a faulty injector (Cylinder 1) and replaced it with a second hand one.

Car ran better but not perfect...

The other day, driving in 3rd at 40Km/h, the car started knocking again.

Drove home, parked it for the night. Tomorrow morning, car drove just fine, however, under load, i can still hear some clicking noise!!! 

I scanned for codes and got P1166.

   
I suspected the fuel pressure regulator to be faulty.i went to actuate it through PP2000, i can hear it make noise but not vibrating though...

However, under the same page, the "flow regulator" is vibrating fine.

I thought it was a wiring issue but wiggling the wires doesn't change anything and the car idles smoothly. 

If i unplug the regulator, the car doesn't start.

Plug it back, and It fires back up.

Can the pressure regulator cause this weird knocking? Was I correct in testing it? 

Any help is appreciated as I'm confused now...