Hello Tech! My first post.. i tried finding people with similar issue but i havent found the solution to my problem just yet. I have a obd-1 PR4 that has a solid check engine light, I know it is not my jumper harness as I used a buddies obd1 ecu with my jumper and everything worked fine. I swapped IC17 and capacitors c14 and c21 already. Nothing! I check solder on Q10 and even resolder Q10 as well as QM3. Any help is greatly appreciated.!

 

Give up on that PR4 and find another ECU.