Hi, I have a '79 240D. My glow plug light used to work fine but isn't coming on now. I have upgraded pencil type plugs. They are wired in series, but with the upgraded wiring so that one failed plug doesn't block juice to the next plug.

Anyway, with key on, I tested current at the metal strip fuse. 12 volts there. I tested each plug after that with a voltmeter and they all have 12 volts. However none are getting warm!

I'm thinking maybe engine ground is the problem? Where exactly does the engine block connect to ground? I need to check that connection next, I figure.

Any other tips?

Thanks very much!

glow plug ground is the head just like a spark plugs ground is the head

If they are wired in series then if you have one bad glow plug then the rest wont work. So I would check the glow plugs since you are getting electrcity to them.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

I don`t know if the 79 is like my 85, but there is a ground cable that connects to the body from the lower left rear of the engine. connects to one of the bolts between the engine and trans..

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

They aren't really wired in series; it just looks that way. The wiring is set up so that each wire connection to each glow plug connects to the next wire in addition to the glow plug itself. So the glow plug is not what passes the current to the next plug; the wiring itself does that.

My car would normally have the coiled metal strips between them but it has been upgraded exactly as described here:

http://www.dieselgiant.com/mercedesdieselloopglowplugrepair.htm

The 2nd-from-last and 4th-from-last pictures particularly.

So basically I have:

No dash glowplug light.
12 volts at glow plug strip fuse and all four plugs.
Cold plugs (I feel them with my hand).

I'm thinking maybe the relay is bad? The dash light had failed to go on a few times sporadically in the past but nothing like this. I'm just surprised I have 12V at each plug but no warmth.

Hmm. Just went out and unplugged the relay and jumped the battery over to the glow plug fuse to manually power the plugs. 12V in each plug of course.

Here's what worries me: the car is not starting. Normally I can start it after a few turns without glow plugs here in Southern California and it's a pretty nice evening. 65 or so right now.

I'd think it was a fuel problem if not for the glow plug dash light issue...

So the plugs are getting 12 volts, that means your wiring is good.

Check the plugs for resistance...I forget the resistance...1 ohm?...check with the dieselgiant tutorial. That;s the quick and dirty way to check the plugs, but they could have the correct resistance and still not light up. The next step is to pull the plugs and connect them to power (briefly) to see if they glow.

Also, you can feel the head near the plugs and see if it gets warm when glowing.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

I've only had the car a month - a previous owner upgraded the glow plugs and wiring.

So I just pulled out the #1 glow plug. Connected it to a 12V 6A battery charger and no "glow". I could even touch it with my bare skin no problem.

Just measured the resistance - almost 10 ohms. Seems like I have at least one bad plug. I wonder if they are all bad? Maybe I had some electrical problem, or maybe the relay is bad and fried the plugs...?

When you connected the plug to the charger, did you ground it to make a complete circuit? Also I'm not sure 6 amps is enough. The fuse strip in a 300 engine is 80 amps; that is for 5 or 6 glow plugs. I think it would be better to use a battery to test the plug. Connect the hot side of the battery to the terminal of the plug and ground the body of the plug. Use a jumper cable so you don't cause sparks at the battery. Hydrogen gas can ignite, causing the battery to explode. A good plug will get red hot.

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1980 300 TD

1997 Dodge Pickup/Cummins 5.9 12-valve

I think all of my plugs are bad. They had resistance 3-10 ohms, nothing under 1. I did connect one plug to the battery rather than the 6A charger and no glow. And that was the one with the lowest resistance.

No wonder the car won't start... all 4 are bad. I may have had a couple out since I got the car.

6 amps should at least make it warm up slowly. But the high resistance pretty much says the plugs are done. When you order the new ones, you need to be sure to get the right size threads. Since the car used to have the loop style plugs, you probably need the new pencil type plugs with the larger diameter threads.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

Except when one goes out, all of them after that go out.