Hi all. Read a few threads Re: this problem but haven't gotten things working yet. Hoping for some illumination.

Car: 1984 300sd

Problem: Glow plug dash indicator not illuminating - glow plugs not activating

Done So Far (troubleshooting):
*Tested glow plugs with test light to pos on battery. All glow plugs good (new actually).
*Checked strip fuse for cracks/corrosion. Fuse good, cleaned off slight corrosion. No help.
*Opened GLow Plug relay. Original relay broken. Purchased a salvage relay (1994 stamp on back but pulled it from a 1984 300sd myself at salvage yard. Fits my 300sd connections. Tested new relay - good. Dash GP light/plugs still not activating.
*Kicked car, made dent.

I have access to alldata and have a "secret" direct number to MB mechanic tech help. Done what each has recommended.

I know somebody must know. THanks for your great posts already.

 

Thanks for your fast and informed respone ForcedInduction. Had someone touch the relay box and it does click when I turn the ignition. I will check the wires you suggest just to be thorough, but if the relay clicks it's gotta be working, Right? Dash light may be out but I am certain the plugs aren't activating. Need to use starting fluid or let car chug for two mins or more to start it. Visually checked wires to GPs from relay and those all seem good. Will check them for continuity. I'm just surpised that by replacing the old, broken relay with one that actually "clicks" nothing at all has changed in end result (ease of start).

 

check for voltage at the wire going to the glow plugs power their then check at the glow plug. REMEMBER it times out you will have to go back and turn the key off and on again to acctivate it again

 

Let me again thank you for your time on this. Still frustrated. Power wire (red) at relay has constant 11.76 dcV when engine on and 11.11 when off. continuity to plugs between relay and GPs themselves so wires gotta be good. What am I too dense to understand here? Why won't my car start like it's supposed to?

Oh, and of course you're right about starting fluid. I did know that but extreme wisconsin winters demanded extreme measures on 2 occasions.

 

I know - you're probably right. Just hate hunting these GDamn wiringghosts. Great thinking about grounding outside block to see if it glows.

 

ummm, perhaps you've considered this, but have you checked compression or valves? If everything else is working, this sure sounds like a low compression issue.

 

I haven't checked either of those things cycleboy. Could you tell me a little more about why you see a link here? Thanks for your time.

 

I think you should check that because you've checked everything else. If your ignition circuit is working, and it appears by everything you've written that it is; then your hard starting problem could also be a symptom of low compression.

As we all know, engines need a certain minimum amount of compression to run. An engine that is worn and failing will still run when hot, or only start when a fuel with a lower flash point is introduced because it doesn't have enough compression to do so when it is cold. If you can start it with WD-40 and then get it to run fine when warm, and it restarts fine when warm, I think I would look to a potential low compression issue.

Of course, your glow plugs could be all carboned up as well.

 

Great Clarification. Thanks much. I was going to get a diesel compression tester for a friend, might as well bite the bullet and just do it now that I have a good reason for myself also.

Honestly though, I'll be surprised if that's it (or at least if compression's the only problem) - Alldata seams clear that if dash GlowPlug lights are not illuminating there IS an issue with the plug system somewhere. I will let you know the compression results.

 

I guess you could just do a cost benefit comparison then. I don't know what the high pressure compression gauge costs, but the glow plug timer costs about $100. You could start with the cheaper article and then go from there!

Although nowhere in this thread does it say whether you've checked the bulb for the dash indicator to make sure it is working. That would be the easiest and cheapest thing to do at this point.