Bought an old 77 240d w123 from auction. 106k - 4-speed. Mechanic's special - Won't start. I installed a new battery, turned the key - did not get a glow plug light so I bought new plugs and installed them. Turned the key and got the indicator light, then snap! fuse went. Repaced fuse, thinking it was just worn, but new fuse snapped too.
The thing that I'm confused about is that I installed loop stlye plugs, which are OEM, yet the plugs I removed were the newer pin style. Could the system have been upgraded? If so, will it still work with loop style plugs? I assumed that they were interchangable, yet I obviously don't know.
I have never installed plugs, so could have done something wrong? I need to know the correct procedure. Saw a thread by Larry B that said something about the insulators? Any help is appreciated.
Craig

This is one is very confusing.

Pin type glow plugs work in parallel, not series as your earlier car originally came with. Loop type plugs are too large to fit the hole in which pin type fit.

Now, I have heard of, but never seen, an upgrade kit that supplies the circuitry, and I expect bushings, that will adapt pin type plugs to an earlier motor. Did you remove some bushings that were around the pin type plugs? If so, you need to put the bushings back in place and buy a set of pin type plugs.

The insulators I spoke of are to separate the bus bars in a series systems so that they don't short around the heating element of the glow plug.

Good luck,

Craig;
The wiring for pin type glow plugs won't work with loop type plugs.
If you are using the correct connectors and insulators as larry mentioned I would look for a short. During the time that pin type plugs were used carbon soot (which is conductive) probably built up in the glowplug bore and may be grounding the circuit.
Remove the plugs and clean out the bores with drill bit and a gun bore brush.
If you were using the pin type wiring on loop type plugs and burned the fuse you can be sure they are shorted!
MF

Check to see if the engine is the same year as the car.....that would change the glow plug types as well.....if someone changed out the motor to a newer one, and never swapped over the glow plug wiring it may be that the previous owner had this problem all along and neber corrected it.

__________________
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88' 190E 2.3
79' 280CE (Sold)
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73' 450SE
93' 300E
68' VW Bug (what the hell was I thinking!)
99' HD FLSTF

I doubt that it was without the correct wiring. I expect that it was set up for parallel glow plugs, but he put in loops which caused the problem.

Have a great day,

Craig;
If you installed loop type glowplugs and used the wiring from the pin type you would not get a complete circuit through the glow plugs.
If the wires are only on the threaded shaft of the glow plugsthe only path to ground is either a wire shorted to ground or the portion of the plug that is inside the head is grounding.

Pull all the wires off the plugs and check for continuity between the threaded post and the engine block, when you find continuity you've found your short!
If you are going to use loop type plugs you will as Larry mentioned have to use the series wiring and insulators.
MF

The problem is that the end ground strap is being used. Take it off if you are using the late style glow plugs because they ground to the block. You don't need the ground strap.

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
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I'm not sure about the term "bus bar" or the insulators.
They came with small cap on the threaded post of the loop plugs, but seemed like this is only for transit protection? Is that an insulator, if so where does it go?
Today:
I bought a new set of the pin plugs, same kind that came out, but have yet to install them. However, I reinstalled the old pin plugs last night and used a test light to see that there is current to the tip of the plug, but it did not blow the fuse, nor did the glow light appear. The light came on with the loops, but you know the rest - pop goes the tab!
The system is: there is the main wire from the fuse, which goes to the first plug. After that, a series of short wires connecting each. No gound wire at the end.
Is the relay the same black box as the fuse bar; Next to that a wire going to another five prong thingy?
What is the difference in the wiring from the pin and loop? How do I determine what system it is using? These connectors from plug to plug are standard copper wire, nothing fancy. Found four used loop plugs in the trunk, so who knows what system I've got..
I did not remove any adapter or such. Plugs screwed in very easily on both types.
I also purchased a non running 77 300d, and thanks to this site it now runs great. This is a great site! Thanks for the help.
Craig

I guess this a pin system. Removed one of the old pins, installed a new plug and tested for Glow light, yep - got glow. Went ahead and replaced all 4 of them. The glow system seems to be working, or should I say at least the glow light is acting proper. I was happy not to hear the pop of another fuse.
Tried to get er fired up, nut no luck. Maye the compression is too low. What else can a non-mechanic try on this mechanic's special?
I pumped the hand prime. Filled the canister filter w/ a diesel additive, thought that might help, guess not.
Read something about tranny fluid in the cylinder to help compression? If so, can I put it through the glow plug hole? How much. Heard it's bad news to use strarter fluid. Again - any help is much appreciated.
Craig

kcn,

Sounds like you're making some progress. As I suspected, your car has probably been converted to a parallel glow plug system. Before you go any further, put a voltmeter or test light on each plug individually with the key on to ensure that you have about 12 volts at each individual glow plug. I am assuming that you have individual wires to each glow plug, rather than a wire that daisy chains from one plug to the next. If you have 12 volts at each individual plug, I think you're glowing okay.

Now that you have checked all glow plugs and have ensured that they are glowing, if the car still doesn't start, you need to crack open each line at the injector one at a time while someone is cranking the car. You should see fuel dribble out of each one. If you see fuel dribble and you have cracked open all of them in turn, and it still doesn't start, you need to check compression.

If no fuel dribbles when the lines are cracked open, make sure you have fuel in the main filter. Use the hand pump until you here a hissing at the top of the main filter.

Good luck,

I do not have a wire to each plug. I have the christmas light kind.
I don't know, but these are not blowing the fusable link. Will the light turn on if the plugs arn't working?
Thanks again.