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  #1  
Old 07-30-2012, 10:37 AM
lae lae is offline
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W123 '79 200D glow plug help

Hello all, I'm new here and this is my car:
http://i556.photobucket.com/albums/ss9/RetroHomeSlice/Mercedes%20w123%20200d/DSCF9106.jpg

A 1979 200D - same engine as a 240D, but a shorter stroke. The 200D wasn't sold in the US, presumably because it's too slow. It shouldn't have been sold in Europe either; this thing is glacial!

Anyway. When I bought the car, it wouldn't start. I didn't have a lot of free time, so I sent it to a classic-friendly garage; they replaced the glow plugs and wiring. After that it started, albeit a little slowly (perhaps five seconds of cranking) on cooler days, but starting straight up on warm days. This morning, however, it wouldn't start. Glow plug light came on as usual. I looked under the bonnet and the live wire between 2-3 was glowing red hot! There'll be a voltage drop somewhere in the wiring so the first and second plugs aren't getting any juice. I can't test this at the moment because the plugs work on the old push-pull starter, and I don't have a glamorous assistant to hold the button out while I poke around with a multimeter (taking a live off of the battery could work, though).

Anyway. I took everything apart:


Cleaned everything up and put on the lower wires:


Then the upper wires:


Put it all back together, and it's still glowing. Originally the car had loop-type plugs with a single live wire in series. However, I can't seem to tell whether these new plugs are loop-type or pencil-type... and it also appears to be wired in parallel. I don't know why it has two (upper and lower) sets of wires either - I haven't seen that on any other car.

Can somebody shed some light on this, and advise me on how to put it back together properly? Figuring out whether the plugs are loop or pencil is the first step. I'd rather not have to remove them!

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  #2  
Old 07-30-2012, 11:16 AM
vstech's Avatar
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I've never seen dual wires either. they are not pencil plugs, as the pencil's have a short stud, and your plugs have long ones.
My advice is to search on here, and see if you can find the proper wiring for your plugs. someone with more knowledge on them should chime in shortly.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #3  
Old 07-30-2012, 12:41 PM
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The wires on a properly wired parallel loop plug system should glow red when they operate so that's not an issue. The issue however, is, what the hell is going on with that wiring system. I cannot imagine that the wiring is correct and I seriously doubt that your glow plugs are actually working. Now, I have not seen a 200d loop plug system in person but I have had loop plug systems on other models. In principle what must happen is that the voltage comes in on one wire, goes down the plug, thru the loop, back out the plug and on to the next plug. This means there has to be an inlet wire and an output wire on each plug and they MUST be separated by an insulator. The way your system is wired, the input wire is directly connected to the input wire of the next plug so there's no reason for the current to go thru the loop. I think someone who didn't understand the system wired your plugs and what you are doing is expending current heating up the wires and not sending any current thru the plugs. You need to look at how a 616 240d loop plug system is wired (there are pictures on here somewhere) and rewire your system to mimic it and I think it will work.

I also don't see a ground wire or a hot wire in your system so I actually don't understand how it's working at all.
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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
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  #4  
Old 07-30-2012, 01:37 PM
vstech's Avatar
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dieselgiant has some good info on both the original wiring, and how to update to modern plugs.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #5  
Old 07-30-2012, 03:16 PM
lae lae is offline
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Aha, I thought the wiring looked a bit suspicious. I took it apart and jiggled it back together into proper series configuration - but still nothing. I tested the input for the first plug and it came up at 26 volts (!) but the output was zero - I suppose this plug (and maybe others) has fried, hence it not starting.

Thanks for the advice, everyone. I'll get some new plugs tomorrow and hopefully I'll get it running again!

It's doubly annoying since my invoice specifies 'rectify wiring'... I'll have to give them a ring tomorrow. I think I'm well within my rights to ask for a refund, even if only for the labour.
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  #6  
Old 07-30-2012, 03:56 PM
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Did you install a ground wire from the plug nearest the front of the engine to the block? Without that ground wire, current will not flow. It has to go from output of the plug nearest the front to the block. You can use an ohmeter to confirm that you have a continuous circuit from the input on the first plug to the output on the last plug.
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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
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  #7  
Old 07-30-2012, 04:12 PM
lae lae is offline
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Yes, I made one up out of a bit of the now-superfluous copper wiring. Since it's called a resistive wire... does this mean that it won't work as a ground cable?

I forgot to test its resistance specifically, but I'll do so tomorrow. I would still suppose that the first plug is fried, since current does not flow through the output (tested on the output of the plug itself, not the wire). Or am I doing things wrong? I don't have any experience of electrics... or diesels... or Mercs!
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  #8  
Old 07-30-2012, 04:42 PM
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That wire should work I think. Jump the hot wire to the input of the second plug (ie--the output of the first plug) and see if you get flow then. That would confirm a bad first plug.

Where are you? The UK?
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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
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  #9  
Old 07-30-2012, 04:59 PM
lae lae is offline
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Yup, I'm in the UK.

If it doesn't work, what gauge of wire should I make a new ground strap from? Will 8-gauge do?

I may upgrade to pencil-type plugs. It seems a much better system, and according to dieselgiant, there's no need to change the relay.
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  #10  
Old 07-30-2012, 05:42 PM
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It depends on what relay is in your car. If it's the same relay as a 79 240d US version, yes, the original relay should work. Pencil plugs are much better.

The OE ground wire is a braided wire.
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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
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  #11  
Old 07-31-2012, 03:50 AM
lae lae is offline
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I'm not really sure what relay I've got, actually. It's not on the inner wing (fender) like later models, but there's a box on the bulkhead containing five little wires (in a push-on configuration) then wired afterwards is what I can only assume is the relay (two inputs, one output that goes to the glowplugs). It doesn't appear to be either an under-dash relay nor a wing-mounted relay!
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  #12  
Old 07-31-2012, 05:44 AM
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The 1979 200D with pull knob has no relay.

Here you can see how you should wire the glow plug. One wire as an input, the other one an output, with an insulator between them.



Here you can see the entire engine, but it looks slightly differently, as this is a key starter, with a relay and without the thermo-time switch.



But your glowers look like pencil glowers to me, but take one out to confirm. It is important, as the wiring is entirely different for pencil or loop glowers.
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  #13  
Old 07-31-2012, 08:35 AM
lae lae is offline
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Fixed it. Well, almost.

The first plug was not outputting any voltage, so I bypassed it and wired the remaining three in series. Pulled the starter button and the glowplug light came on for a good 20 seconds, rather than 2-3 seconds as it did before. The remaining three plugs are getting voltage and glowing properly. Pulled the starter to the next notch and vroom! It started up immediately. Good stuff.

I'll be replacing all the plugs with proper Bosch items, and asking for a refund from the garage that did the re-wiring.
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  #14  
Old 07-31-2012, 04:12 PM
lae lae is offline
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Quote:
Originally Posted by Govert View Post
The 1979 200D with pull knob has no relay.
I think I've solved the problem now (and thanks very much to everyone who contributed, it would've been a bit of a headache without your help!), but just out of interest, how does the system work without a relay?

As far as I can tell, my system is wired thus:
1. Push-pull knob
1.a. possibly a relay under the dash. Haven't checked.
2. A five-pin box bolted to the centre of the bulkhead, directly behind the engine
3. An inch below this, a box containing the strip fuse (which I assumed to be the relay). This has two inputs, and one output going to:
4. Glow plug live wire

The strip fuse box looks like:


Does anyone know for certain that I can upgrade to pencil-type plugs without needing a new relay?
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  #15  
Old 07-31-2012, 05:03 PM
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I can't recall anyone on here converting a gorilla knob system to pencil plugs. I don't see why it wouldn't work although I suspect the current draw will be different enough that the glow plug light may not work.

__________________
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
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