I don't know on an 87 but on my 85 if you short the t-terminal under the hood(the one you short out when you set the timing) and turn the key to "on" (don't start the engine) the check engine light flashes. Count the flashes and it tells you the code #
I have a FSM for 85 and can tell you what the codes are, I doubt they changed them from 85 to 87
