Won't always start
 

My 1985 300TD almost always starts after a normal glow plug cycle. Sometimes it just cranks though and doesn't fire. When that happens it is immediately obvious because this engine always starts after very few revolutions. When it passes the Xth revolution (say 5 although it is hard to count) I know that it isn't going to start. If I turn the key off and immetiately back on to start (no glow plug wait) it fires right up. Could this be a sticky vacuum shut-off on the ignition lock? Maybe it's the shut-off on the injector pump sticking?

Who's seen this before.

-Tad

Any difference in temps? Hot or cold engine?

I would suspect a weak glow plug.

Might be a little air in the fuel system from time to time. Do you have a new style primer pump?

New style primer pump. Hot, cold doesn't seem to matter. What's odd is that I can flip the key off and immetiately back on it starts without a glow plug cycle. I might try to replace the vacuum shut-off valve on the ignition lock and see if it is sticking.

-Tad

Awhile back, I read about a situation where the linkage for the IP was slightly out of adjustment and causing something similar. When the linkage was disconnected from the shut-off lever and moved to the "detent" position, the lever mount and the socket on the rod did not match up. A couple of turns on the rod end cured the ailment.