91 ford E-350 (diesel 7.3L) stalls after 3 seconds at start-up ?

My '91 ford E-350 Econoline Diesel 7.3 L
is starting hard. When engine is cold (not-
run-for-over-eight-hours) it starts up right away,
BUT ONLY RUNS FOR 3 SECONDS AND STALLS.

It can't be the glo-plugs, because it does start right up on the first try. But after it stalls, I have to crank for about 45 to 50 seconds before it will start. Lots of blue smoke after it starts, but being a diesel, can't tell if that is normal.

_______ any guesses ?
_____ Shade-Tree-Mech.