I had similar difficulties when I first got my 85GN years ago. From memory I think my problem had something to do with the little black box on the cable assembly that connects to the ALDL port connector. Seems to me there was a switch in that box that had to be in a certain position. I can't find my manual right at the moment so I can't refresh my memory to tell you which position is correct.
I'm assuming you already checked the port for clean contact pins?
If that doesn't help contact Ken at Accelerate Tech he is the inventor
HTH
Peter
Are you following the insturctions? I want to say the car has to be turned on, not running but the key to the on position. Otherwise you might have a bad cable. What computer are you trying to run it on?
Shouldn't matter what computer, unless you don't have a good serial port on it. When you try to get the readings are you going to the section to set up what type of vehicle? Try setting up for the 87 ecm not the car type and see what happens.