My car is suddenly having a hard time starting in the morning and the glow plug light on the dash sometimes lights up when I turn the key. And sometimes not. Sometimes it doesn't light up for the regular 5 seconds or so. I suspect I have a bad glow plug in there. Is there a way to test the individual glow plugs?

I am presuming you have the pencil type glow plugs that have a 12mm hex head on them.

Go to the diesel giant web site and look for Mercedes Diesel Glow Plug Repair and there is a guide to how to check the glow plugs with the Ohm setting on an electical meter.

Cheap electrical meters are had from Harborfreight for around $6.

You just need to disconnect the connector coming from the glow plugs to the glow plug relay on the US cars driver's side on the fender well. In theory the bad glow plugs will not have the same ohm/resistant reading. This is the easiest one.

The better test is to acquire a glow plug reamer. Remove the plugs and test them with your car battery. When tested on the battery the tips should start glowing. If it starts glowing in the middle of the element that plug is no good.

With the plugs out you fill the grooves/flutes of the glow plug reamer with thick grease to trap the carbon. You screw it in and out and clean off he carbon and regrease as needed and do that to all cylinders to done.

Then you hold the manual shutoff in the shutoff position (so no fuel is injected) and have someone crank the engine and it blows out an particle the fell inside the pre-combustion chamber.

I put a never-seize compound on the glow plug threads when I assemble them.

There is also youtube videos on them and removing them and so on.

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84 300D, 82 Volvo 244Gl Diesel

On any of these diesel cars, one of my favorite mods is to install a 1/2.1 amp usb charger with voltmeter between them in place of the cigarette lighter(easiest on 210, then increasingly difficult from 124 down to 123/126)
This will tell you when your brushes are getting worn, alt is bad and most importantly about the functioning of the glow plug relay. Otherwise you have to depend on the dome light to visualize the voltage drop.

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97 e300d, 78 300Dt, 95 E300d, 94 E320 estate

I'll probably just order new glow plugs tomorrow. But, I did have a second to pull out plug #1. I measured resistance and it read .00. Then I connected it directly to the battery. The very tip of it glows bright orange. Now, why does it read .00 ohms? It seems that measuring resistance is always a crap shoot.

How, exactly, did you measure resistance?

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Black lead on the threads where it goes in to the block (ground). Red lead on the electrical threads at the tip. (Yes, my meter was set for resistance, not volts.)

You might have the wrong Ohm setting on the meter or poor contact.

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84 300D, 82 Volvo 244Gl Diesel

I have it set at 20 ohm setting. I'm sure my contacts are good. I think I'll try measuring amp flow if I can figure that out. I've never done that before.

Might it be the glow plug relay? It's a complex little thing.

My method of testing glow plugs is very dark. Remove injectors. Turn off all lights and be in the dark. Start glowing the plugs and look down the injector port. If you can't see the glow, the plug is bad. If they are all off, could be someting else, but if one works, they all should work.

If you removed the Injectors in theory, you would need to install new heat shields. I have not priced them for many years gut the cost on the internet was like 5 times lower compared to buying them at some local Autoparts store. You can do as you said but it insures some expense.

Pulling out the plugs allows you to ream or otherwise clean out the carbon around the tip of the plug. some members have claimed that clearing the carbon out allowed for easier starts all by itself.

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84 300D, 82 Volvo 244Gl Diesel

I believe it is supposed to be on the 200 ohm setting.

I have had one bad glow plug that glowed in the middle of the tip. It is likely the amps were ok on it. In any event I hook up an alternator type dashboard type amp meter in series with a glow plug and it pegged out at the max the gauge read which was 60amps and as the plug heated it settled down to around 16 amps. That is a DC meter.

Not sure what happens if you use one of those inductive AC ammeter.

Sorry I can't be more help. I don't remember where to find the specific how-2 threads.

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84 300D, 82 Volvo 244Gl Diesel

In the attached pic is one of the Harbor Freight type electrical multi meters. For testing the Glow Plugs it is set at 200 Ohms.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Diesel911, you are correct that the het shields would need to be replaced. $1.50 each. For me it was worth the cost to find out which glow plug was bad. It is such a simple approacj that solves the unkown. If it glows it is good. For me is was a good value and i was doomed to succeed in finding the bad plug.

THanks Diesel911!!! that pictures helps. Is that a good glow plug in the picture? IS that what it's supposed to read? What is 1 . ??