I just bought a decent 78 300D with a no start condition when cold. The previous owner had replaced fuel filters and glowplugs. This did not help so I immediately did a run down of the glow plug system with my manual and a voltmeter. According to the meter all is in specs EXCEPT the light stays on far too long. With a small shot of ether (I know this is a no no) the car would start and run perfectly...no misses, no valve noise and no excessive smoke. I consulted my local injection pump guru and he said it may be losing prime. I hand primed the pump and this did not work either. No. 1 leak off leaks some but the engine DOESN'T miss! Upon further consultation, contaminated fuel became an issue. I pulled the fuel tank and low and behold there was a gas smell!! There was lubricity in the fuel so it did have some diesel left in it. I pulled the tank and flushed the sustem out and filled with known good fuel, changed filters agian and I still have the problem. Finally, my question is this: I know that gas can take out the pump, but why does it run so well? This also doesn't address the glow plugs when cold. I should add that once at op temp (175-180) the car can be shut off and restarted up to 30 minutes later although the crank time increases proportionly to the length of time it sits. PLEASE HELP, I AM AT MY WITS END WITH THIS CAR!!!!!!!!!!!

I would first adjust the valves and perform a compression test if necessary. Also, Check out the following link to see if you have the same kind of fuel problem as stated in the post:

300SD Hard start after not used for a few days

Low compression (caused by worn out rings or tight valve clearnance) will give a cold starting problem. If you have a fuel problem as in the link above, you will not smell diesel or see smoke from the tail pipe during cranking.

Good luck.

David