As you've probably discovered by now, the socket on the body synchs with the back shutter _only_ and not the lens shutter. It'll fire the before the lens shutter opens, which doesn't do much good.

Try a different synch cord, try using a PC Tip Conditioner tool, or try bending the center pin of the cord's plug slightly off-center. If none of these cure the problem you'll probably need to have a repairman replace the lens' pc outlet.