My wife's 1979 240D (432k) has been running very well. I replaced the glow plugs about a year ago and it starts easily even in cold weather. I replaced the starter about 2 weeks ago because the old one lost the solenoid bolts and broke. The car has very little smoke and good power.
The car started normally and about a mile from home,
while she was accelerating up a hill to pass a cement truck, it just quit. According to her, no coughing, chugging or any engine noises. She said there was a cloud of black smoke as it died. She said she wasn't sure though if the smoke wasn coming from the cement truck or the car. She walked home about a mile and got me to go look at it. When I tried to start it, the battery was dead and it wouldn't turn over. I got it towed home and put jumper cables on it. It turned over normally, started and ran for about 20 seconds then died. The battery is less than a month old. The alternator about 2 years. The alternator was working at the time I replaced the battery. The old one had 2 dead cells.
Thinking it seemed to not be getting fuel, I replaced the filters and primed it with the manual pump. Now, it simply won't start. Sometimes it kicks like it wants to start but nothing. I tried spraying some starter fluid in the air intake but still nothing.
The glow plugs are getting electricity and I'm pretty sure they are ok. The car started normally on it's last trip.
She said the only abnormal thing it has been doing is running-on for the past month.
I visually checked all the vacuum lines and they seem to be fine.
I don't think the problem is major (at least I hope not), because of how well it has run since we got it 150k ago.
Any ideas of what can be wrong or things I might do to find out what is wrong would be greatly appreciated.