No glow plug light - PeachParts Mercedes-Benz Forum

mbzr4ever · #1 09-25-2007, 11:24 PM

Hi everyone,

Glow plugs - new problem for my 1979 240D w123. Ran great up to about a week ago. Then its been sitting as I was taking the 300E around.

So I go to start it today, and the glow plug light does not turn on. The other lights on the panel are on - battery, etc. Radio works, as does headlights. Very slight dimness in the headlights when I try to crank, so I'm thinking its not the battery, but the glow plugs.

What do I look for next? Some fuses? Can I use a voltmeter to test? How do I test the glow plugs to see which, if any, need to be replaced?

Please be easy on me, I'm a female trying to restore my project car. Thanks for any responses.

AdvisorGuy · #2 09-25-2007, 11:34 PM

Happened to me 3 months ago with my SD. Check the fuse in the glow plug relay box. mine is on the drivers wheel well under the hood. Just follow the glow plug wires to it and pop the cover. It's a bi-metal strip with 2 screws in it but is actually an 80 amp fuse. Got 2 from my local foreign parts supplier for $.95 each.

mbzr4ever · #3 09-26-2007, 12:02 AM

95 cents each. You are soooo lucky!

OK, I looked at a fuse that was about center against the back (firewall?) - maybe the 240D is a bit different layout? There was a wire going directly to the glow plug line.

The metal strip was intact, it was held down by 2 screws inside a black plastic flip top box.

While I was at it, I looked in the regular fuse box, just for the hell of it. Everything looked normal there, BWDIK?

jkoebel · #4 09-26-2007, 12:31 AM

Mine just went out today, very hard starting now...

Diesel Giant has a "troubleshoot your glow plugs" section if you want to go there and check it out.

mbzr4ever · #5 09-26-2007, 12:33 AM

OK, will check it out.

Good luck with yours, at least yours starts. I'm afraid if I crank it too long, the battery will go out.

toomany MBZ · #6 09-26-2007, 09:52 AM

This happened on the SD, I checked the ohms on the GP's, one was bad. Replaced all, I'm funny that way, back to normal. You might want to pull that fuse strip to inspect thoroughly, just to make sure it's good.

mbzr4ever · #7 09-26-2007, 09:13 PM

I got a reading before and after the strip and going to the first GP. Then nothing after 1 and nothing afterwards.

So, I going to pick up 4 new bosch GP Friday when I go to Oahu.

BTW, is the GP relay for my car the black plug against the wall next to the GP fuse? (It did not look anything like the diesel giant pictures.)

At first I tried to take if off and it would not budge, and the outer rim cracked off from using too much force. I should probably order a new one, but I want to make sure that's what it is called.

toomany MBZ · #8 09-26-2007, 10:59 PM

Quote:

Originally Posted by mbzr4ever

OK, I looked at a fuse that was about center against the back (firewall?) - maybe the 240D is a bit different layout? There was a wire going directly to the glow plug line.

The metal strip was intact, it was held down by 2 screws inside a black plastic flip top box. that is your relay, it contains the metal strip, right?

How did you check GP's? With ohm meter? At each female connection at plug, grounding other lead? On mine there are plugs inside the relay "box". One for timer, the other for each GP, where you touch red lead. Don't know about a '79. Thought those relays were under the dash. Good luck.

redbaronph123 · #9 09-27-2007, 08:37 AM

since you have a 79, your glowplug system is in series. 1 bad glow plug and no starting for you. Verify first if you are getting juice to your plugs. Or at least after the strip fuse. If you are getting 12v at the strip fuse, then you can move to the glow plugs. Check the resistance of each plug, you may follow the tests in dieselgiant's how to site.

Hopefully you just have 1 busted plug.

#10 09-27-2007, 09:40 AM

An ohmmeter won't always tell the whole story, at least not on my '83.

All of my plugs checked okay w/ the ohmmeter. Fuse(s) fine. Still no glow plug light. Car started fine but ran rough and stumbled if I didn't press the pedal in about halfway while starting. I knew that some of the plugs were working, but I likely had one or more than one that was very weak.

Replaced all five glow plugs. Light now comes on and all I have to do is bump the key over to start and the motor fires right away.

Check the big strip fuse and the relay, but you will likely need to just replace all five and you should be in good shape.

TurboSDL · #11 09-27-2007, 04:46 PM

i just replaced all my glow plugs and my car wont start, i have to run jumper wire to the plug wires from the relay

mbzr4ever · #12 09-27-2007, 09:11 PM

I have an ohm reading after the metal strip to the 1st GP. The needle just jumps all the way over to the right. And nothing after the first GP, so, I'm guessing its the first GP.

I'm just going to replace them all at the same time - I called earlier today and they are holding them for me for pick up tomorrow.

Just to verify:

the metal strip is really a fuse, isn't it?

the relay would be the black plastic looking box with wires/pins against the wall to the right of the above mentioned fuse, correct?

toomany MBZ · #13 09-28-2007, 06:27 AM

Quote:

Originally Posted by mbzr4ever

I have an ohm reading after the metal strip to the 1st GP. The needle just jumps all the way over to the right. And nothing after the first GP, so, I'm guessing its the first GP. One of 'em anyway.

I'm just going to replace them all at the same time - I called earlier today and they are holding them for me for pick up tomorrow. Good.

Just to verify:

the metal strip is really a fuse, isn't it? Yes.

the relay would be the black plastic looking box with wires/pins against the wall to the right of the above mentioned fuse, correct?

On mine the strip fuse is in the relay box. Which is black plastic with wires, and plugs bolted to the drivers inner fender.

barry123400 · #14 09-28-2007, 08:51 AM

On a 1979 240d the relay is located above your right knee when sitting in the drivers seat. I do not think it was relocated to the engine compartment and changed to a black color until 80-81.
To access it if ever required you remove the panel underneath the dash and it is a silver box bolted to the support arm of the pedal assembley. Also I would test and keep any good glow plugs from your old ones. If you where to have one of the new ones go bad at some point. One of them could be a replacement that you have on hand.

vstech · #15 09-28-2007, 10:24 AM

while you are looking over your glow plugs. I would stop by autozone and pick up one good loop plug to get the car going for now, but;
take the time to investigate http://www.dieselgiant.com/mercedesdieselloopglowplugrepair.htm
this turned my slow to start 79 td into an instant starter every time!
plus, if one plug goes out, the rest still work!
DG includes in the pictorial upgrading to the modern GP relay, it is nice, but not needed on the 79. my original relay is working the pencil plugs very nicely.