To recap:  I began by doing some pulls to check out a new software tune and verify the calibration on some pressure sensors was correct.  During a third gear pull something went wrong and the wastegate duty cycle dropped to zero and the tone of the vehicle changed.

I found a wideband O2 sensor plug had come out of the downpipe changing the tone but I still couldn’t figure out why the boost had dropped so suddenly:

I was able to determine that the sensors were generally within 1 psi of the vehicle map sensor – shown above.

I disconnected the compressor signal lines from the N75, separated the individual lines from the tee, and attached a sensor to each line to monitor the pressure in the housings independently.  Those results were not good, one K03 was boosting to almost 25 psi and the other not at all.

I started the disassembly process to try and find the source of the problem.  After looking in the charge pipe and exhaust pipe I moved onto taking the motor out to inspect the turbocharger.  After taking it off I cannot find anything wrong with it.

I’m thinking of having it rebuilt just for the sake of it, ‘while I’m in there’, and if I do will send this ones partner along with it for the service as well.