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  #1  
Old 06-22-2005, 11:50 AM
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Glow plug relay clicks off quickly

Well i purchased my '83 300cd last tuesday and i love it. It is by far my favorite car i have owned so far... and here come the issues that i knew would arise..

When i turn the key to let the glow plugs warm up i hear a click from the center console area (i'm assuming its a relay) .. then about 1 second later i hear a second click (assuming relay again), if i wait for the glow plug light to go out, it's harder to start and smokes/shakes until it gets going....

If i turn the key 5 or 6 times after it clicks off, the car starts much smoother.. so i'm assuming that the glow plug relay is closing then opening again, not allowing the plugs to heat up... what would cause this? a bad plug causing a ground? a bad relay?

Any help would be appreciated

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Old 06-22-2005, 02:37 PM
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Congratulations on your purchase and welcome to the Forum.

It could be any of the things you mention, but the Glow Plug Relay in my SDL also varies the time it powers the glowplugs according to the ambient temperature. when it is cold it 'glows' much longer than when it is hotter outside.
I would do a saerch on "Glowplug Relay" and see what you can find.
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  #3  
Old 06-22-2005, 04:27 PM
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The relay for the glow plugs is located on the driver side fender under the hood so the clicking in the center console is probably something else...however I still suspect there is a glow plug or relay issue since you have to cycle it so many times to get a smooth start.
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  #4  
Old 06-23-2005, 09:54 AM
LarryBible
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Check the number one glow plug. On your pin type system, the relay measures the resistance of the number one plug essentially using it as a temp sensor. I would check resistance of that plug AND pull the plug and visually inspect it. Often these plugs will have good resistance, but have a hole in the shell.

Good luck,
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Old 06-24-2005, 11:36 AM
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I also had this problem when I first bought my SD. If you have a digital volt meter
or any resistance measuring device you can ohm out each glow plug and I bet you will find one that is open. I did and replacing just the one solved my problem. The resistance should be around .6ohm depending on your meter. The important part is that they should all be within .2ohm of each other.

hope this helps. SKI
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  #6  
Old 06-24-2005, 11:51 AM
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The clicks from relays in the center console area are probably due to the climate control system settings.

The click, almost a clunk due to the amount of current it draws, for the glow plug relay is from the left fender well. When it trips you will see a noticable brightening of the battery and warning lights on your dash.
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  #7  
Old 06-24-2005, 10:37 PM
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jgroover,

Do a search on cabin light. It will help you diagnose the GP relay.

P E H
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Old 06-26-2005, 11:21 AM
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testing how to

I tested my jetta's glow plugs last year but i forget how to...

for the resistance test... where do i put the leads? one on the threaded end and one on the 'nut' that you use to tighten the plugs in? also do i need to disconnect the bus from the glow plug?

All your help is greatly appreciated!
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Old 06-26-2005, 02:37 PM
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Quote:
Originally Posted by jgroover

for the resistance test... where do i put the leads? one on the threaded end and one on the 'nut' that you use to tighten the plugs in? also do i need to disconnect the bus from the glow plug?
The easiest way is to pull the connector at the glow plug relay. There are five sockets inside. Test each socket. The second lead goes to a good ground.

BTW, you need a good meter for this. You are looking for a reliable number around 1 ohm. 100 ohm scales or above won't cut it on an analog meter.
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Old 06-30-2005, 09:15 AM
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glow plugs all tested good

Well i tested the glow plugs last night by checking the resistance between the glow plug connector and a ground and they all tested at .9.

I'm thinking the next thing to do would be to pull a plug and look at it for any holes in it... but i think before doing that i should test the relay and clean up the fuse.

How do you test the relay? I've tried the search but can't find any direct details.

Thanks for your help!
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  #11  
Old 06-30-2005, 10:10 AM
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jgroover,

Did you do a search on cabin light like I sugested?

You can test the GP relay by listening to it and observing the cabin light. When the key is turned to run position, the relay should click on and the cabin light should dim slightly. That shows the GP are drawing current. THa GP relay should stay on this mode for about 45 seconds.

The GP light in the dash doesn't mean much. Its just an approximation of how long to wait before you engage the starter. The GP light may turn off to early but the remedy for that is to wait longer before you engage the starter. The GP relay does not turn the GP off when the GP light goes off if the relay is working correctly.

P E H
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  #12  
Old 06-30-2005, 10:16 AM
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jgroover,

Did you do a search on cabin light like I sugested?

Your GP are OK and any problem lies somewhere else.

You can test the GP relay by listening to it and observing the cabin light. When the key is turned to run position, the relay should click on and the cabin light should dim slightly. That shows the GP are drawing current. The GP relay should stay in this mode for about 45 seconds.

The GP light in the dash doesn't mean much. Its just an approximation of how long to wait before you engage the starter. The GP light may turn off to early but the remedy for that is to wait longer before you engage the starter. The GP relay does not turn the GP off when the GP light goes off if the relay is working correctly.

P E H
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  #13  
Old 06-30-2005, 10:17 AM
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peh,
is the amount of time the GP's are energized dependent on the ambient temperature? ie: when it is colder outside the GP's are energized longer? and vice versa for when the ambient temperatures are warmer?

i notice my GP dash light stays on longer in the winter...
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  #14  
Old 06-30-2005, 11:54 AM
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84300DT,

The time the GP dash light time on is supposed to be dependent on the temperature of the engine. It tells you to wait longer to turn the key to the start position when the engine is cold. This time can be out of calibration. The time the dash GP light stays on one of my 300SDs is much too short and if I don't wait longer, the engine is hard to start. Simple solution is to wait about 10 seconds after the dash GP light goes out to crank the engine and it start instantly.

But, the time the GP relay energizes the GP is fixed and is about 45 seconds. I.E. the GP are not shut off when the dash GP light goes off. This 45 second time is interrupted when the starter is energized on the older Diesels. Some of the newer Diesels, however, continue to glow the GP while the starter is running and some even beyond the engine starting, probably for emissions reasons.

P E H

Last edited by P.E.Haiges; 06-30-2005 at 12:21 PM.
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  #15  
Old 06-30-2005, 02:05 PM
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thanks for the help guys. I actually asked too soon.. i had a basic idea of how to test it and i figured it out during lunch. The relay does click off... i even put the key into the glow position and tested the voltage from the prongs on the relay (where the glow plug connector would go) and they all read 12+ volts so the plugs are good and are getting power. So next start after it's been sitting awhile i'm going to let the plugs glow til i hear the relay click and see if it still runs rough at first.

But i also noticed another thing - which may be connected.. when i start up and it runs rough, my oil pressure only goes a little about 2 .. but goes right up to three with some throttle.

When i start it up after is warm or cycle the plugs a couple times and it starts up smoothly, the oil gauge goes up to 3... connection here?

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