See also this thread, he has a 98 W210 with the same motor (OM 606) as yours.

http://www.peachparts.com/shopforum/diesel-discussion/332580-e300-glow-plug-success.html

On the cruise control, while you have the intake off, since it's at the left rear of the block:

Trace the cable to an 8 pin connector on the left inner fender.
Unplug the connector and look at the pin side. The pins are numbered 1-8 on the block, pin 8 is not used.

Use a meter to measure pins 1 to 3 you should have about 3.5 k ohms no matter where the fuel linkage is aka the swing arm on the actuator.

Pins 1 to 2 you should go between 3.5 k and zero as you move the fuel linkage. Pins 2 to 3 should be the opposite, when 1-2 is at zero, 2-3 should be 3.5 k and vice versa. Can't remember which movement causes which value but that is not important here, just that the value sweeps up and down as you move the linkage.

Now get a couple test leads and put your meter on dc amps. Put the meter in series with the - post of the battery and pin 4. Then put a jumper from the + post of the battery to pin 5. You should hear the servo motor spin up and it should draw less than 200 mA.

Now disconnect the meter leads and jump straight battery power to pins 6 and 7. You should hear a click, this is the engagement solenoid.

If all that checks out it is probably the amp, it is under the dash. Search threads by JamesDean, he has the story on that part of the system.

Thanks for the help fellas.

I would just resistance check and change out any glow plugs that show open circuit pretty well first. There are risks with these engines and their glow plugs. From all the posts of people having issues believe them.

One thing if possible is I would initially loosen a glow plug with the engine still running and up to temperature. Wearing safety glasses and gloves. Just in case any junk gets blown in your direction. Use a good specific anti seize on the new plugs as well when installing them. It is not unusual for a used example of these cars to be sold with broken off glow plugs either.

Do not run the plug out with the engine still running should be needless to say but has to be done. It could be almost suicidal to do. You only want to get the glow plug started.

Barry12345,
I have never run an engine with the intake manifold removed, but I guess it wouldnt make any difference since its a NA engine.
But I think thats a great idea to heat the engine up to make it eaiser to remove the plug, and Im all for making any job eaiser, my idea is always work smarter not harder.

Not my ideal originally . But the moment I read the ideal it made good sense. A running engine with the temperature up to normal operating levels is going to have the aluminium head expanded more in the area of the glow plug. More in my opinion than an engine that is turned off and up to full operating temperature.

At least one member has used this approach. Maybe even more that I am just not aware of. You want every known possible advantage when dealing with glow plugs on those engines.

606 Glow Plug Removal
 

Has anyone tried to ; remove fuel filter
remove injectors , disconnect glow plugs, liberally spray wd-40 into cylinders ,, crank repeat ,crank, repeat , then remove glow plugs ? this may help to remove carbon from the inside ? 1996 w 300,000 miles & 1997 w 371000 miles ,

naw, all that will do is wash all the oil off the cylinder walls. To "soak" , each cylinder ought be brought up to TDC and then the chamber filled with solvent.But I wouldnt go there.

The reason the GPs are old is becuase they are stuck. Get them nice and soaked with some "Freeze-off" or Thrust , which only takes care of the threaded portion.

Like others have said, you need the head hot to try and remove them.

Odd as it sounds, these diesels run with the intakes off. I freaked out the first time.

I broke a GP off in my 606 and it can be removed. A big PITA or a big mechanics bill. But once they;re all new, simply keep them swapped out.

606, even w/o a turbo, is a damn fine running engine. Except in a drag race. :(

606 Glow Plugs- W-D40
 

I now have over 600000 miles with the 606 , have been with a few nasty ones , pre soak may help , reamer also .