Any ambitions diagnosticians? 1985 300D hard starting

[ATLD]

Gentlemen,

I am completely baffled by this one. I have a 1985 300D non-turbo that has always run extreemely well. I take very good care of the car and do all the maintenance myself. It has 265,000 miles on the clock and is my daily driver.

All of a sudden (late last week) the car became very difficult to start cold (ambient temperatures above 60 deg F). It was acting similar to a very cold start (below 10 deg F) or after opening the fuel system. The car cranks and smokes while cranking; it will start after about 10-15 seconds cranking. Runs fine thereafter and starts fine warm.

Fuel filters were replaced a year ago. The valves were lashed last FEB and are not past the 12.5k mi interval. Glowplugs were all replaced about four years ago with Bosch plugs. 1 had failed early this year and replaced with a Beru plug (since I was annoyed with the Bosch plug failing prematurely).

One thing I had noticed was that the glow plug indicator light would cycle for less than 2 seconds or NOT AT ALL and was inconsistent. After repeated testing, the glow plug light would only come on intermittently thereafter. Diagnostics with the power and signal connection to the glow plug timer (12vdc battery, gnd, 12vdc ign, crank signal, and light) all checked OK so I replaced the relay this morning. Light now functions correctly but the starting problem remains...

Fuel solenoid appears functional.

ALL fuel injectors (and spill hoses) were replaced to correct a nailing problem fall 2007. Fuel filters replaced also.

This car ALWAYS started immediately above 40 deg F. Now, all of a sudden it acts this way. The car is about at the mileage for the next oil change which I will complete this weekend. I plan to also change the fuel filters and possibly investigate valve lash but I am baffled about the immediate onset of this problem. I would suspect the preglow system but it appears to be working now.

Any thoughts?

Thanks,

-Adam