code 20

I have a 92 ls with a b17. the ecu was trippin code 20 and 23. i replaced the alternator and code 23 went off but 20 is still on. the car still wont start. thought if i replaced the alternator the electronic load detector would not be tripped? any suggestions? anyone come across the same problem?

okay i ran out of ideas so i took it to a local shop and they put in a new distributor to see if that was it and it still did the same thing, the dash lit up like it was gonna start but no it didnt.