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My 1978 300D with 250K on the clock, has this pesky tendency of intermittent hard starting. Requiring me giving it key for at least ten seconds before it will start. Here are my details, I say "intermittent" because in the cool of the morning, when I'm leaving for work (5:30am) after glowing the plugs it fires straight away without hesitation. I drive my little yellow tank to work @ 70 mph for 17 miles like a champ. After working my 9 hour shift (3pm warm out) I cycle the glow plugs like normal but have to keep cranking till it starts. Here's what I've done so far. Replaced the primary and main fuel filters, I've replaced the primer pump with the later Bosch style. Newer starter, newer battery, newer upgraded glow plugs, cleaned and replaced the main fuse on firewall. Did a valve adjustment about 7 months ago. Diesel purge about a year ago. I've tried cycling the glow plugs twice before attempting a start, (FAILED). I have hand primed injectors before attempting a start assuming I may be getting air in the lines, (FAILED). On my days off from work of course I'm sleeping in and putzing around the house. So when I go to start the Benz for the first time it's usually around 11am. Sometimes it will start right away but mostly I have to keep cranking to get it started. Running around town doing errands if I shut it down for lets say 10-20 minutes it's okay (not always). but if I'm gone long enough for the car to completely cool off, I'm cranking. Because of the way it cranks in the cool of morning (and intermittently during the course of the day), I'm assuming it's not a lack of compression issue. UGH!! Any thoughts or better yet, any HELP?

Sphinx144

crank shaft position sensor?