1987 744Ti 170K

Still chasing a bogging down when boosting problem with this recently acquired turbo. Good compression, free flowing/non restricted exhaust, all turbo/intercooler plumbing seems fine, AMM swapped for known performer, doesn't seem to have vacuum leaks. Boost gauge goes right up half way on the pressure side of gauge and immediately bogs down and lurches somewhat until you let up on the accelerator and it smooths right out. When it bogs down it changes tone a little as well; it developes an intake sound like a carbureted engine does with the air cleaner off under heavy acceleration (not that pronounced but similiar) The boost however stays at the half way point on the pressure side. All I have to do to smooth it out and cruise at speed (70-80mph) is back off of the boost. Does not seem to be running rich and no black smoke that I can see. When I disconnected the knock sensor the performance seems to go to the dogs in every way so I am guessing it is working properly (Guessing is the key word there)

So one earlier suggestion was to check the coolant sensor and I would prefer to do that at the ECU connector. Can someone direct me to the correct pin number?

Any other thoughts from the description feel free to jump in with your suggestions. My work puts me on the road for about a week starting tomorrow so I will get back at this when I return. Thanks.

Randy