Hey,

My turbos are boosting fine at 10psi below 4500rpm, but when 2nd turbo comes in, I can't get more than 7psi.
I got this problem since a couple months already and I still need to check different things. (turbo control actuator, vacuum lines, etc)
I don't know if it's relevant for this problem, but I often notice a weird squeaking sound during the turbo transition (around 4,5k rpm) , I can hear it especially while boosting moderatly (not WOT)
Maybe some of you guys experienced this problem already and can point me out where to look at first

Today, I've been able to record the sound with a decent microphone, you can hear it here :
https://www.youtube.com/watch?v=3rwMHZzWViI

 

Not that I know anything about the cause of the lack of boost, but...

Squeaking indicates to me one of two issues: a) a boost leak during transition, or b) an actuator/wastegate, etc. squeaking as it moves, maybe indicating something hanging up.

 

Yep, to me it sounds like a leak, definitely.
In the meantime, I filmed the turbo actuators' rods with a GoPro, and discovered that the precontrol didn't move at all !
I unmounted the air intake box to check down there.
Everything looked ok and correctly plugged, but when I wanted to unplug the precontrol/waste gate solenoids, I found out a broken nipple on the WG solenoid.
I'll change it soon, hopefully the leak was coming from here.