I am not 100% sure on 1987, but this is true on later C4's
The computer wants your engine to run optimal, so if it is running rich or lean, it changes the pulse length of the injectors to make sure the car is running optimal.... If you increase pressure, it should be because you do not have enough to start off with... when you tune your fuel pressure, you need to do it by air/fuel ratio, and not PSI... it doesn't matter what PSI you run at, it matters what your air/fuel ratio is. When you tune, disconnect your battery (this will re-set the computer back to factory) then change your pressure, in very small increments... There are many problems while fuel pressure tuning, the main one being the computer...
It is like working with a partner who doensn't tell you what they are doing and when they are going to do it.
I didnt know that but I will try to hook up my laptop into the car today and see if I got some data of it,,I have tryed it before but I couldnt get any contact but I recived some new tips today and I cant wait to come home to try it,,