I installed M2 stage3 ECU on Friday and did a trackday yesterday, running about 10-11psi on the track. I got home and everything was fine. Few hours back I took the car to the carwash and was still fine. After I took it out of the carwash and came to piece of straight (after few minutes), I accelerated to redline and got some secondary boost problems - primary boost is fine then at transition it falls to 8psi then keeps falling to redline (and the car feels weak) whereas it was fine just 30minutes ago.
My boost was fine before, also I got no smoke out of exhaust during boosting.

Any hints on what could it be ?

 

Check for a blown off vacuum line...

 

Which lines to check - On the actuators or under the UIM ?

 

I would start with the ones on the firewall side of the UIM. Do a quick check for the line to the pressure chamber with the check valve on it.

Basically, just open the hood and start looking around.

 

Found it !
It was the hose that comes on the black box in front of the UIM Dunno what the box is calles though.

 

Pressure chamber...so a hose was disconnected from there?

 

Yes, the front hose was disconnected. I still have stock hoses. I know I know... I need to do the silicone hose job, but as long as she's running I can't find time to do it