Have you tried the key on/off procedure?
Put your key in the ignition...turn it to the on position (don't engage the starter or start the Jeep) so, turn it to the on position, then turn it off...then turn it on...then off and finally turn it to the on position for a third time...leave it there and count the number of times the check engine light flashes.
When you get 5 and then 5 again it is finished with the codes.
I hope that makes sense....key in...on...off...on...off...on and watch the check engine light.
'91 stock YJ, red, 4cyl, 5 spd. I wonder how long that configuration can last???