I have a 1979 300d,Ive only had a couple of weeks ,I do know this.
1 the glowplugs work and glow bright orange
2 there is voltage going to glowplus
3 I have a electric fuelpump,so I know the injector pump is getting fuel
4 I have to crank for about 20 seconds before starts,and even then I have to push on footfeet to keep running ???????then it will idle
5 turn engine off go to Menards ,do a little shopping come out ...hard starting again,and the engine is warmed up.