Typically most diagnostic computers aren't readily available for OBD-1. If you have an OBD-2 that's a different story.
As for checking engine codes...
if you take a look under the glove box, you should find a blue connector, disconnect it.
take a small piece of wire...a couples inches or so...
stick it where the connector goes into (the female part)
it will make a closed loop (in the female adapter)
turn the key into the on position, and count the engine light blinks.
short blip = 1
long blip = 10
it will cycle through all the engine codes, and then it restarts
there is typically a short pause between codes, and it will have a long blink first if the code is above 10.
i.e. long long short = 21
use the search feature (the red search at the top right of this site) to understand what each code means. goodluck