The quick answer is no. It didn't exist at that time.
OBD is On-board Diagnostic. Porsche 928s didn't offer any diagnostics until model year 1987. The Model Year 1988 and newer provided a round diagnostic plug under a panel to the right of the passenger seat. The Porsche diagnostics used at that time was unique and requires a special plug and code reader.
Later model cars of most types began to have standardized plugs, OBD II is the latest standard.
I have mentioned this in another post, but I am sitting on the fence, fix everything or make it electric. I recently got it back from my mechanic - 10K lighter and still lots of work and the EV movement is gaining momentum.