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  #1  
Old 12-17-2003, 02:59 PM
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Join Date: Nov 2003
Location: Tiki Island Texas
Posts: 1,049
series glow plugs

Im sure this is not the proper way to test the plugs, but for just down and dirty. I turn on the key and cycle the plugs. #1 only warm #2 very warm #3 hot hot hot #4 hardly warm. I assume they should all be hot these are the old loops wired in series. What I assume is the relay is not what is pictured in my manual, but 2 or 3 inches right of the strap fuse a module that all four wires hook into seem to plug into a very sloppy, floppy connection through the fire wall doesnt easily unplug and Im afraid of tearing off a wire coming in from the ignition
HELP WANTED
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89 300E
79 240D
72 Westy
63 Bug sunroof
85 Jeep CJ7
86 Chevy 6.2l diesel PU

"The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane."
Marcus Aurelius
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  #2  
Old 12-17-2003, 03:07 PM
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Join Date: Nov 2003
Location: Tiki Island Texas
Posts: 1,049
Also - wires route to under brake booster then to a black box on the RF fender - there are two - what I would think are relays of the same # in there. This is a 78 sold new 79 240D - Thanks
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89 300E
79 240D
72 Westy
63 Bug sunroof
85 Jeep CJ7
86 Chevy 6.2l diesel PU

"The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane."
Marcus Aurelius
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  #3  
Old 12-17-2003, 03:18 PM
Marshall Booth
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It's not clear to me from your description that you are determining ANYTHING about the function of the plugs but may be monitoring mostly the effect of the couple of resistance wires (the serpentine shaped wires that connect between a couple iof the plugs) which generate and dissipates into the engine compartment more than half of the heat the system produces.

When the system is working properly and energized, there is a little more than a one Volt voltage drop across each glow plug (from the top to the bottom connection onn the plug) when measure with a DC meter. The voltage drop across each plug will be about the same. If one is much higher than the others, that will be the bad plug.

The actual voltage measured across each plug will drop some with time as the plugs heat and current drops. You may have to activate the system several times to measure all the plugs as it will cycle off after 30-60 seconds.

Marshall
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  #4  
Old 12-17-2003, 04:21 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Relay is loose -- it's screwed down through the firewall, I think.

There are two zigzag wires in the system, these get VERY hot (they are reisistor links).

To test the plugs themselves, check the connetors and then the voltage to ground at the plugs. There is a voltage chart in the manual, I'll look it up at home this evening (late) -- there is a fixed voltage drop for each element and for each link.

If you have voltage at the last plug, they are working. IF one is open or you have a grounded plug, they either won't work at all (no voltage past the open one) or the filament is shorted. Only way to check that is to pull them out to see.

I't's not unheard of for them to get crapped up with so much carbon from bad running that they short across the filament and don't heat properly. Can be fixed by carefull cleaning.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 12-17-2003, 10:55 PM
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Join Date: Nov 2003
Location: Tiki Island Texas
Posts: 1,049
Thanks I was just messing around and cycled the plugs to see. Heat from the resistor wires probably was all I felt. Re the relay what Im seeing on the fire wall seems just like a flat plug, and is mounted in a rubber push fit grommet that has no screws. What are the two relays mounted on the wheel well? The box could accommodate several, but this car doesnt have any accessories except the electric sunroof. Unfortunately the backroads Ive mentioned around here helped me wipe out my oil pan this PM got home safe with plenty of oil thank you but need to start another thread
Thanks
__________________
89 300E
79 240D
72 Westy
63 Bug sunroof
85 Jeep CJ7
86 Chevy 6.2l diesel PU

"The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane."
Marcus Aurelius
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  #6  
Old 12-18-2003, 01:33 AM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
AC and aux fan, probably. I think they are similar to the W115 chassis, so electric window relay will be on the passenger side firewall. Could be wrong, but I know the AC and aux fan relays are in there.

the glow plug relay is on the other side of the firewall, I think, under the air intake grille.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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