Okay, probably not haunted, but weird. I changed all my glow plugs last week. Still, the number one glow plug, the one closest to the firewall, will not heat up. So I changed it again for another new one. I thought I had a faulty plug. Still, the second new one also does not heat up. I cleaned off all corrorsion on the system when I changed the other ones. And since the plugs are all in series, if the first one is not getting current, then the other ones wouldn't be getting it either. But the other ones work fine. THey all heat up but for the first one. Where the bus bar connects to the plug is cold on this one, but hot on the other ones.

So how is this possible? I'm not Catholic and so am not really entitled to the services of a priest.

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1975 300D

The number one Glow Plug is the one closest to the Water Pump.

Are you getting Voltage to the Plug nearest to the Fire Wall and do you have the Stock Loop/Filament type Glow Plugs?
If you are not getting Voltage to the Glow Plug at the Fire Wall you need to check your Fuse or your Glow Plug Relay may be shot.

In the Manual if the one at the Fire Wall is not working (but getting Voltage) the Glow Plug/s in front of it could be bad (that would be the #4 Glow Plug if you have a 5 Cylinder Engine).

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84 300D, 82 Volvo 244Gl Diesel

Hi Diesel 911, yes, the number 4 glow plug is heating up.

I thought the circuit starts at the firewall. At any rate, the number 4 plug is hot, but not number 5. I have loop plugs

Where is this glow plug relay, or fuse? But wouldn't it be working of the car is starting and at least 4 plugs are hot?

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1975 300D

Now that I think of it I am not 100% sure your year has a Glow Plug Ralay. the 1976s do.
If there is a Fuse Box you sould be able to trace the Wire up to the Fire Wall and see if there is a Plastic Box or Cover. However, if any of the Plugs are getting hot your Fuse must be OK.

Since the Voltage goes into the Top of the Glow Plug (at #14) and through the Glow Plug and comes out at (#3) under the Ceramic insulator (#9) and goes down the zig-zag wire (#1).

If wired correctly and the Insulator is working do not see how the Plug itself could be bad and continue to give voltage to the other Glow Plugs to get hot.

Make sure that the Insulator is doing the Job.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

The only way I can imagine that happening is that the inlet and outlet wires on that plug are touching each other so current is not flowing thru the loop. How precisely do you know that plug 1 is not getting hot? Have you removed it from the block, kept it wired into the circuit and observed the loop with the key in the glow position?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Are your Glow Pluts wired as in the pic below. Thie item on the far left is a Temp Sensor?

Please note how they are wired compared to the insulators.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Yes, my plugs are wired just like that.

I know it is not getting hot because I can touch it. The other ones even make a bit of smoke from the grease burning, and they are hot, hot, hot. The fifth one is cold

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1975 300D

Check continuity thru the plug using an ohmeter with one probe on the input surface and one probe on the outlet surface. Compare the plug nearest the firewall with another plug and see if the results are the same. Also, confirm that the insulator is doing its job of separating the two wires.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I ruled out a bad plug, since i tried 2 brand new plugs there and both don't get hot. It is possible, in theory, but the odds against both brand new plugs being bad are very remote.

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1975 300D

One thing we don't know is whether this condition is normal. Can anyone with a loop plug system confirm that the plug that receives electricity first actually gets hot under normal conditions?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Okay, I just looked at the plugs again. I noticed that the two squiggly connectors glow hot. The two straight connectors do not.

If this is normal, then I see where I was fooled. The number 5 plug would therefore be the furthest away from a glowing hot connector, therefore it would not have warmed that the other plugs have when touched.

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1975 300D

It would be considered rare but the insulator on the firewall plug may have a conductive trace. Change that insulator with number ones glow plug insulator. That is the last one in the circuit at the front of the engine. .

See if the firewall plug now heats. I want you to use the insulator off of the number one glow plug to prevent over voltaging the other plugs if that ceramic insulator on the firwall plug is conductive.

But first. If you have a voltmeter another test for a short through the insulator is to measure the voltage across that plug when the glow plug circuit is active. Normal voltage drop is 1.2-1.6 volts I imagine. This is measured from the wire that feeds the firewall end plug and the output non flexiable buss bar where it leaves the same glow plug.

This is a very simple circuit so your options are limited. If you do not have the insulator between your power feed to the firwall glow plug and the output buss wire is a real possibility. Or the ceramic insulator has developed a conductive trace. Again unusual but not impossible.

It is basically impossible to have two glow plugs with the internal element shorted to itself but that is the only thing left if the first two things check out properly. I really suspect the not wired correctly firewall glow plug in the chain is the issue here.

That is normal as in the old series glow plug set up resistance wires where used wastefully to reduce voltage to the glow plugs. For some reason the glow plug manufacturer supplied glow plugs with a 1.3 volt rating. I believe this was a leftover from the six volt battery days. They could have used the same plugs with no resistive squiggly wires on six volt systems. In fact I imagine they did.

Your update helps. There apears to be nothing really wrong. Just verify the voltage drop across the firewall plug but I think you will find the 1.3 volts or so there. Again if so then there is nothing wrong.

Well, I checked the voltage as you described and it read 0. I checked the battery and it was 12.

I then checked the voltage between the plug 1 and plug 5, and it was 9.

Does this sound normal?

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1975 300D