I am a fairly new diesel owner (93 300D 2.5 Turbo) with my first glow plug problem. I have not been able to find a manual CD yet, so I am a little in the dark. Symptoms are basic, Glow Plug idiot light does not come on when you go to start the car, and comes on for a few minutes after. I read that you can test the resistance in another thread, but I do not understand exactly how to do this. Can someone walk me through this and share any tips or tricks regarding replacing GPs? Do I need to replace all of them? or just the faulty ones.


Thanks in advance for all the help.

With all the work necessary at getting to the GP's you would be well advised to replace em all at the same time.
To test them one could use an Ohmmeter with the low scale looking for resistance only a couple Ohms for a good GP, disconnect the GP timer and test from there. Or use the car battery to momentarily apply voltage and verify that they indeed get hot (watch out and don't get burned in the process!)
Oh, yes, replace the GP fuse, located under the top cover on the timer module I believe on that model. It tends to get hairline fractures that cause the timer to lose its voltage. Only about $1.50 from the Partsforum. I keep a spare in each of my diesels, having seen them fail in that wierd way (its called metal fatigue, common in high current fuses.)
Dieseldiehard
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body. '87 300D w/ Sportline suspension. No more '79 300TD w/ 617.952 engine at 367,750, it was my annual driver to Texas and I sure don't miss it poor A/C heater system!

Thanks. Can you provide a little more information?

Where is the Glow Plug Timer? What does it look like?

Do you know of a site where I might find a picture of the process?

The module will have a plug that carries current to the 6 glow plugs, that is where you check resistance using an Ohmmeter.
The fuse is a short piece of grey metal that is held down by two philips head screws. Don't short anything out while changing the fuse, disconnect the battery unless you are extremely careful. I don't have the same model as you so I am not going to go any further to avoid making an error or confusing you further. You need the CD if you have no experience with Mercedes diesels, or at least a Chilton's book (I wonder if they have one for the '93 diesels yet?)
Use the search function on the Forum and you may find exactly what you are looking for.
The Pre Glow timer module in the OM603 appears like:

Attached Thumbnails

 

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body. '87 300D w/ Sportline suspension. No more '79 300TD w/ 617.952 engine at 367,750, it was my annual driver to Texas and I sure don't miss it poor A/C heater system!