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  #1  
Old 07-16-2007, 02:25 AM
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If dash indicator glows can a glow plug still be bad?

If dash indicator glows can any glow plug still be bad? They are loop/filament type plugs, wired in series. The car is a 76 240D
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  #2  
Old 07-16-2007, 02:46 AM
diametricalbenz's Avatar
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Nope they are all working. They are wired in series like you said.
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  #3  
Old 07-16-2007, 03:12 AM
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Hi khickey.
I've been following the problems you've been having but haven't really chimed in because I'm still pretty much a noob and don't know anything about w115. But I was wondering if you ever set up an alternate fuel tank using a juice bottle or some such. This will rule out a clogged tank strainer or air leak somewhere in the fuel lines. Something like this.

http://dieselgiant.com/injectorcleaning.htm
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Last edited by slarson80; 07-16-2007 at 03:25 AM.
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  #4  
Old 07-16-2007, 04:06 AM
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Uh just because the light does not come on doesn't mean they are effective in doing there job. I had a 300D that just would take for ever to start and not at all when cold. Replaced the glow plugs even though the dash light worked fine and then the car started imediately.
On that note the light for glow plugs does not work on my 240D 75 do the glow plugs get hot when you pull the nob to turn on the car?
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Old 07-16-2007, 11:49 AM
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Yes if the light is working the all the glowplugs are functioning. But they my not be functioning to their fullest. GP's generally slowly start heating less and less. So you may have an engine full of tired but still functioning GP's
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Old 07-16-2007, 12:02 PM
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Quote:
Originally Posted by Biodiesel300TD View Post
Yes if the light is working the all the glowplugs are functioning. But they my not be functioning to their fullest. GP's generally slowly start heating less and less. So you may have an engine full of tired but still functioning GP's
In other words, yes the glowplugs can still be 'bad' if the light still works.
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  #7  
Old 07-16-2007, 12:12 PM
Craig
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Originally Posted by pdxwaker View Post
In other words, yes the glowplugs can still be 'bad' if the light still works.
Well, they can be "weak" if the light still works.
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  #8  
Old 07-16-2007, 10:14 PM
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Most of what has been posted here is well intentioned, but wrong. The glow plug system on a 115 240D is a simple series circuit. 12 volts >>> gorilla switch >>> glow lamp >>> #4 glow plug >>> #3 glow plug >>> #2 glow plug >>> #1 glow plug >>> ground. That's it. If the glow lamp lights, the circuit is passing current. If it doesn't light, the circuit is not passing current.

With the gorilla knob held in the glow position, you should have some voltage with respect to ground at all points in the circuit. Start by measuring voltage at the #4 glow plug. If no voltage, the problem is not in the engine compartment. If there is voltage on #4, work your way forward, checking each plug. When you find the one without voltage, the previous plug is open circuit.

Don't discount the possibility that some nitwit has assembled the wiring and insulators incorrectly. It is not uncommon for someone to put it back together incorrectly when changing a glow plug. Look closely.

Edit: Let me have your E-Mail address via PM. I have a pdf of the glow plug circuit, slightly too big to post.
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Last edited by Palangi; 07-16-2007 at 10:20 PM.
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  #9  
Old 07-16-2007, 11:30 PM
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Glow plugs get weak over time. They don't just quit working one day. When they get weak their resistance gets high which allows less voltage to go by. Each series GP is supposed to use between .75-1.25 volts. If you measure the volts on each side of the GP the difference between the two numbers is how much voltage each plug is using up. If the number is higher than .75-1.25 then the plug is bad or one its way out. If you get a voltage on the supply side and 0 volts on the other side then the GP is bad.
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