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  #1  
Old 03-29-2011, 03:32 PM
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Quick Glow Plug Question....

When I go to start my '93 300D the glow plug light doesn't come on, but it will turn on after it starts. The car starts perfectly when dead cold outside, but is pretty rough on said start up. Does this indicate that a glow plug(s) is out? If so, how do I go about checking which one is out?
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  #2  
Old 03-29-2011, 03:50 PM
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124.128/602.962/722.418
 
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Read this document. Especially page 12 which discusses system faults.

http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/15-0705.pdf
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  #3  
Old 03-29-2011, 03:59 PM
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Thanks for the link! I'll check it out.
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  #4  
Old 03-30-2011, 12:51 AM
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Go to the Diesel Giant Site and see how to check the Glow Plugs with an Ohm/Volt Meter. The 617.952 instructions will work except that you have one more Cylinder.

This will give you a good idea if the Plugs themselves are OK.

(This is not a recommendation to buy parts there.)
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  #5  
Old 03-30-2011, 07:01 AM
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Quote:
Originally Posted by Diesel911 View Post
Go to the Diesel Giant Site and see how to check the Glow Plugs with an Ohm/Volt Meter. The 617.952 instructions will work except that you have one more Cylinder.

This will give you a good idea if the Plugs themselves are OK.

(This is not a recommendation to buy parts there.)
his instructions are on a 6cyl motor.
several hints for changing the GP's under the intake manifold.
http://www.dieselgiant.com/glowplugrepair.htm
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Old 03-30-2011, 10:57 AM
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Quote:
Originally Posted by vstech View Post
his instructions are on a 6cyl motor.
several hints for changing the GP's under the intake manifold.
http://www.dieselgiant.com/glowplugrepair.htm
Even better.
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Old 04-01-2011, 01:44 AM
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Quote:
Originally Posted by vstech View Post
his instructions are on a 6cyl motor.
several hints for changing the GP's under the intake manifold.
http://www.dieselgiant.com/glowplugrepair.htm

Thanks for the help! I will get this looked at as soon as I have time.
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  #8  
Old 10-11-2011, 12:00 PM
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It's taken me a long time to finally replace the glow plugs, but as the weather started to get colder it had to happen. I replaced all five glow plugs, reamed the holes, replaced the intake manifold gasket (it was leaking badly anyway). The glow plug light now comes on, and turns off as normal. But I'm still stumped on why the engine is starting so rough! It starts on the first rotation every time, no matter what the temperature. The engine runs perfectly for about five or six seconds, then it gets extremely rough with a lot of smoke until it warms up. This happens every time I start the car, unless the engine is already somewhat warm. What gives?
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  #9  
Old 10-11-2011, 12:41 PM
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Your post-glow feature is timing out too quickly, you probably need to replace the relay. When you start the engine, your pre-glow relay energizes the glow plugs again which improves combustion to keep all cylinders firing while the engine is still cold. Post glow should last longer when your engine is cold, there is a temperature sensor in the circuit as well. I suppose the sensor may have failed but I don't know how it would behave if that happened. Maybe if you unplug the temperature sensor, it will default to the longest possible post-glow?

If you're really handy, you can take the relay apart and replace the capacitors in the timing circuits.
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  #10  
Old 10-11-2011, 02:18 PM
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Does your glow relay have an external temp sensor? If so the sensor or wiring might be bad. My guess is the temp sensor is on the water pump housing.

Sixto
87 300D
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  #11  
Old 10-11-2011, 05:54 PM
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All the 124.128 2.5L 300D (s) got the Electronic Relay.

It's capable of "Sensing" shorts and other Electrical anomalies that might damage
the Wiring and the Chassis. No Glow Plug Relay 80 amp Fuse.
It would be well worth your time and trouble to carefully disassemble and repair it.
IF after physically checking all connections (+Etc.) WITH A MULTIMETER it still malfunctions.
I believe that what's the matter is "Connection" (Wiring loose or shorted) OR
External Component (The Temp sensor that determines "After Glow" timing).
[B11/7]
The Pre-Glow ReLay does have it's Own separate dedicated GROUND.AND
if the Ground's not "Clean,Bright and Tight" the ReLay will mal-function.[W9]

The Link that Old Wolf posted in reply #2 of this Post will greatly assist.
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Last edited by compress ignite; 10-11-2011 at 06:28 PM.
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  #12  
Old 10-24-2011, 06:44 PM
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Quote:
Originally Posted by sixto View Post
Does your glow relay have an external temp sensor? If so the sensor or wiring might be bad. My guess is the temp sensor is on the water pump housing.

Sixto
87 300D
I unplugged the coolant sensor, and the glow plug light stays on for the entire cycle and the car starts perfectly (just glowing for 5-10 seconds). Plug the coolant sensor back in, and the rough starting becomes an issue again. With the sensor unplugged, is it running the glow plugs all the time? or just the full cycle? A new relay is probably needed because I do not have to expertise to repair the one on the car. Any thoughts?
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  #13  
Old 10-25-2011, 05:08 PM
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Quote:
Originally Posted by Harrison W View Post
A new relay is probably needed because I do not have to expertise to repair the one on the car. Any thoughts?
??? Sounds like you need a new $20 temp sensor rather than a new $200 relay.

Sixto
87 300D
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