That is what mine was doing!!! The rocker arm retainer pin broke and the rocker arm was under the valve cover bouncing around. The smoke was caused by the unburnt fuel getting past the valve and partly burning off in the exhaust. Not really sure why GM designed the retainers to be nylon.
I have a 1994 6.5 TD "F" code. When I was pulling the intake manifold off, (lower), in order to get to the rocker arm that had the broken pin :mad2:. I noticed there were two little, thin metal plates covering the center holes in the heads. They were covering/blocking the hole between the head...