There is no such thing as a Diagnostic port until you get to 92 and newer Honda's, and even then the 92-95 isn't usable by any normal scanner Ive ever seen so really its 96 and newer.
The 88 Accord LXi is OBD0, PGMFI. The ecu has either a single LED or a set of 4 LEDs depending on how they blink or how they light up you can decipher the code.
It should, SHOULD be the 88-91 style that blinks Morris code, long blinks are first digits, short blinks are 2nd digits or single digits.
But theres a possibility it could be the 84-87 style that has 4 LEDs that represent numbers, depending on which ones are added up you can find a table that shows the codes.