Glow Plug Light Not On Anymore...87 300D Turbo

[a2t]

Recently I noticed glow plug light not on anymore. still starts, but with dropping temps here in GA, it DEFINITELY stumbles until warm.

I have the 3 pdf's from MB that say how to test all the electrical stuff.

Rather than go through all that (cuz I suspect its a faulty GB - its got 248k on em!) is there a quick and dirty way to see if the plugs are getting hot?

Can I just touch the threaded end to see if they are warm, or will they get to a billion C at the exposed end ? Dont wana burn!

I guess I could pull all 6 plugs out and go key on to see if they all glow. Replace one that doesnt. Except getting the plugs out looks like a pain, intake prob has to come out.

Any help here would be much appreciated!

[TheDon]

dont touch the plugs at all.. they get very very hot... check the fuse a small crack can cause the glow system to not work

[a2t]

Originally Posted by TheDon

dont touch the plugs at all.. they get very very hot... check the fuse a small crack can cause the glow system to not work

Good to know!

Any idea where exactly the fuse is located? I thought it was within the timer relay box, but the manuals have this tendancy to ZOOM in on the item and give vague instructions on where it actually is.

[TheDon]

i know where it is in the W123's... but an easy way to find it maybe is to just follow the glow plug wires to where they go... my wires originate from a box then to the fuse then to the plugs etc..

[a2t]

ahh good idea.

ill give it a try.

while Ive got an expert online, any way to easily remove the GP's? Or does the intake mani definitely need to come out 1st?

[Hatterasguy]

I am not sure if the W124's are set up like this, but I bet they are. Check the GP strip fuse, they fail all the time.

[Johnhef]

fuse is in the relay box, just remove the cover and check it closely.

quick-n-easy on testing glow plugs is to remove the connector leading off the relay to the plugs and you'll see it numbered 1 thru 6. get your meter, set to resistance and check each of them while grounding the other test lead. anything up to 1 ohm is good, anything way over that or open circuit is bad.

for example- I just did plugs on the SDL tonight, its light wasnt coming on:
1) .8 ohm
2) .9 ohm
3) Open
4) .8 ohm
5) 16.5 ohm
6) .8 ohm

Now I'm not sure if its a set rule but most of the ones I've seen that the light fails to come on for, usually have 2 or more failing. one out and the light will usualy come on.

it's easier to just remove the intake manifold- you'll need two gaskets for going back on, unless yours are fairly new. the one I did tonight just crumbled when I took it off. You can typically get away with resuing the large green rings on the intake tubing.

[a2t]

I'll try that, thanks!

Strip fuse is good.

[a2t]

Originally Posted by Johnhef

fuse is in the relay box, just remove the cover and check it closely.

quick-n-easy on testing glow plugs is to remove the connector leading off the relay to the plugs and you'll see it numbered 1 thru 6. get your meter, set to resistance and check each of them while grounding the other test lead. anything up to 1 ohm is good, anything way over that or open circuit is bad.

for example- I just did plugs on the SDL tonight, its light wasnt coming on:
1) .8 ohm
2) .9 ohm
3) Open
4) .8 ohm
5) 16.5 ohm
6) .8 ohm

Now I'm not sure if its a set rule but most of the ones I've seen that the light fails to come on for, usually have 2 or more failing. one out and the light will usualy come on.

it's easier to just remove the intake manifold- you'll need two gaskets for going back on, unless yours are fairly new. the one I did tonight just crumbled when I took it off. You can typically get away with resuing the large green rings on the intake tubing.

#3 was 750 ohm
#5 was 30,000 ohm

The others were right around 1 ohm

Guess that means its time to remove the mani, huh? I'll just replace all of em since they are relatively cheap.

Any tips for getting that mani off? And thank you very much for the tips.

Edit -- 2 more dumb questions. Are the cylinders on my 124 ordered 1-6 heading aft?

And, I can now see my head has the number 603 016 14 1 -- is this the dreaded #14 head?

[dieseldiehard]

that is a #14 casting allright. Not to worry if its ok now just take care not to overheat it and it should last a long time.
Right, #1 is the frontmost cylinder.
Remove the intake manifold with the lines still attached underneath. You will still need new plastic clips as they tend to break getting them off.
You will need a ball head hex driver or a universal jointed driver. I can't remember which, 4mm or 6mm? Wiha makes a clever hex key with a tiny c-clip incorporated in it that holds the socket head screw so it won't fall off, a nice tool to have on this job. After the manifold is off, stuff socks or something into the head to prevent letting debris into the openings.
Getting all the air out of the injector lines will arise, its a frequent problem and there have been numerous posts on this but leave the lines loose at the INjectors and crank about 15 seconds, with the accelerator pedal down, pause a while to let the starter motor cool the repeat this until fuel is running onto the block, then tighten the nuts at the injectors and continue cranking until it runs.
There are mechanics that will replace GP's with the manifold inplace. My hands are too large and I avoid self inflicted pain so I remove the manifold. Besides you probably need to clean the crossover and manifold crud inside that tends to build up (esp if egr is operational!)

[gsxr]

You can change the plugs with the manifold in place but it's a nightmare. I'd pull the manifold. No need to remove the injection lines - leave them attached to the injectors and injection pump. Replace ALL SIX plugs... AutoZone has the best price I know of, and they have Bosch Duraterm plugs. Use Bosch or Beru plugs only - not Monark, Autolite, or anything else. While the manifold is off, use the time to clean things up, use a new OE/dealer manifold gasket if possible (this will have a metal reinforced core, most of the OEM/aftemarket gaskets are paper only). Also replace all the metal injection line clips & buffers - see photos below.

As a 1987 300D owner, read this article if you haven't seen it yet:

[Marcb]

It's more than likely you have 2 bad glow plugs. Mine stopped illuminating the light when 2 finally failed to glow any longer... I agree with Dave, replace all 6 and it is a major PITA with the intake on, but I've done it.

[W12487300D]

I've got the same problem with my 87 300D. How do I check the ohm reading for each glow plug at the relay? I've found the relay and I have a good volt meter. . . While the intake manifold is off, is there anything that I should replace in addition to the glow plugs? Also, I see there are two filters for the intake manifold. Do I need both of them and how do I make sure they are OEM?

[gsxr]

Originally Posted by W12487300D

I've got the same problem with my 87 300D. How do I check the ohm reading for each glow plug at the relay? I've found the relay and I have a good volt meter. . . While the intake manifold is off, is there anything that I should replace in addition to the glow plugs? Also, I see there are two filters for the intake manifold. Do I need both of them and how do I make sure they are OEM?

1) Remove the large connector from the relay. Set your meter to read ohms. Put one lead to ground (intake manifold will work) and the other lead to one female pin at a time in the connector, check all 6. The readings should be all the same, and under 10 ohms each (remember, there's resistance in the wires, etc so you likely won't see the 0.6 ohms you'd get from a new plug tested on the bench.) Anything that's much higher is probably a bad plug.

2) While the manifold is off, replace all the injector line clips shown in the photo above. I'd also replace the 80A strip fuse in the glow plug relay. These get brittle over time and can fail at the most inconvenient moment. I keep a spare in the fuse box as well.

3) Filters? You mean gaskets? They don't have to be OE but all the OEM gaskets I've seen are plain paper, and the OE gaskets are metal reinforced. I prefer the OE (which you'd have to get from a dealership).

[W12487300D]

g1: 3.3
g2: 2.85
g3: 2.21
g4: 2.24
g5: 2.24
g6: 88.9

Replace glow plugs?