First cold morning in Georgia today. Noticed my glow plug light didn't come on at all. Engine started rougher than normal, one or two cylinders weren't firing at first and then cleared up quickly.

Checked the relay later. It made an audible click after about 45 sec. after turning on the key. So sounds like the relay is working. Would a blown relay fuse still allow relay to click at all?

Guessing I've got a couple of bad glow plugs. Want to fully eliminate the relay as a cause simply because it's easier to get to. If I change out glow plugs it looks like I have to pull the whole intake since this is the non-turbo om602.

No.
As you said likely some issues with the actual glow plugs.

If you pull the Glow Plugs you should also ream out or use some alternative method to clean out the Carbon from the glow plug holes.
(I don't know if your Engine has an aluminum cylinder head or an iron one but the below stuff applies to the ones with aluminum cylinder heads and their longer glow plugs.)
If don't think the Glow Plugs have ever been removed if the cylinder head is aluminum it used to be common for the head to break off of one or more of the glow plugs due to corrosion in the treaded area and or carbon build up around the glow plug.

Look for methods to decrease the chance of snapping off the head on the glow plug.
Repair Links Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

Note it you take to a shop to have the Glow Plugs removed and a head snaps off shops usually won't try to remove it themselves because if they damage the cylinder head they are stuck with the responsibility for that.

They usually want to remove the cylinder head and send it to a machine shop. Besides not having the responsibility if they damage your cylinder head the Shop is going to get more $s for removing and re-installing the cylinder head.

Be optimistic but if it is a daily driver plan for another ride to work incase more break.

Use only Beru or Bosch Glow Plugs. Put some never-sieze type compound on the threads when you put them back in.

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84 300D, 82 Volvo 244Gl Diesel

from the manual:

Lamp fails to light up, engine is hard to startor fails to start altogether.Fault: Short circuit on one or more glowplugs, line interruption, preglow time relaydefective.


pull the plug from the relay and check the resistance between different plugs on the relay and the engine block to know which/how many are bad

more info:
https://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/70010.pdf



only the 4 valve OM606/5/4 have long glow plugs and problems with them

You both are amazing. Thank you. Going to go ahead and order all 5 and pull the intake next weekend when I have everything.

Getting confusing information on which Bosch glow plugs I should order. Some sites say the Bosch 80006 and others are saying 80007/80008. Like I said, it's a 1986 190D 2.5 om602.

That is more on the filament/loop type glow plugs where when one plug goes out they all stop working. The only way for the pencil type plugs to short circuit is if the insulation rubs through on the wires and it makes contact/grounds itself on something.

Then there is another issue. In the attached picture is a bad glow plug that appears to work. The problem with it is that it is the tip that is supposed to get hottest not the middle of the Plug (it is a Monark Glow PLug that I had bought before knew about only using Beru or Bosch). Note that that glow plug ohmed out OK when I tested it.

Here is an odd one for you over a year ago my Glow Plug Light stopped working but I was starting normally. I ignored it and about 1 year the light started coming back on normally.

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84 300D, 82 Volvo 244Gl Diesel

IF you can find one of those Mercedes parts sites that has the Mercedes parts list you will see notations to the side that say up to engine number so and so or after number son and so when they have more then one number for the part.

Glow Plug Reamer see attached pic. In the one pic I used vasoline to hold the carbon in the flutes/grooves so that it would show up in the picture. Otherwise I would have used wheel bearing grease as the vasoline melts too easily.

See post #6 for some types of Glow Plug reamers.
1982 240d glow plug dash light come on but bad glow plugs

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84 300D, 82 Volvo 244Gl Diesel