Can a past history of epididymitis cause erectal dysfunction ? the cause of the epididymitis was straining to lift a heavy object 40 years ago.

No relation: Epididymitis will not cause erectile dysfunction, certainly not 40 years later. You're at an age when ED becomes quite common, usually with no particular cause known. (It doesn't matter now, but 40 years ago it was thought physical strain could cause epididymitis. We now know that doesn't happen. It is much more likely you had an infection, e.g. chlamydia.)