USA car? In 1991 no 2 cars on earth used the same EFI DLC
you meant DLC< and is OBD1 car in USA> and varies by engine not told., by you,, nor country, coupe or sedan.
no makers (EFI) use the same tools or protocols on that port nor the pins wired the same. ever.
only the Acura tools work or some $5000 tools in huge shops.
that have very expensive plugins to make 50 car makers DLC TaLK
so here goes;.
DLC diagnostic Logic connector location
aka, scan tool port. or service port. (jack/conn)
besides factory scan tools there are those silly now CEL blink codes.
EFI is called PGM here. FI.
service Check Connector
-is below the right side of the instrument panel, above the ECU. (usa answer not Europe RHD)
the DLC jumper must be inserted
the blink DTC code are here 91 legend.
what pins to jump IDK sorry, google or real Acura service manual is the goal. 1991 is very old are and few on the road now.(running)