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  #1  
Old 05-09-2005, 08:07 AM
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Glow Plug Relay

Just looking for a 2nd opinion. The glowplug dashlight goes on and off like always, however the car won't start.

I'm getting voltage to the glow plugs. But I wasn't able to perform the amp test. Is there anything else that might be causing the "no start" besides the relay.

This problem happened over a couple of days. One day it was hard to start the next nothing.
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  #2  
Old 05-09-2005, 09:34 AM
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I'd suggest a voltmeter and the service manual. Service manual available on CD from here. Buying stuff keeps this "free" web site going.
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  #3  
Old 05-09-2005, 09:49 AM
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rderton,

If you have voltage to the GP, the GP relay is working OK. How long did you wait for the GP to heat? Try waiting for 30 seconds the next time the engine is hard to start. If it starts easily, problem solved: the timing of the GP indicator is out of calibration. Just wait longer for the GP GP heat each time.

If it still doesn't start, do a resistance test on each GP. Use search to find the procedure, key words GP resistance.

Let me know the results.

P E H
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  #4  
Old 05-09-2005, 10:24 PM
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I have the same problem with my 300D right now, it will not start. I have narrowed it down to the glow plug system. I have tested the resistance across the plugs themselves and they test ok, so I am guessing the plugs are good. The glow plug light on the dash does not come on but did last week. I have noticed that when I turn the key, the light does not come on, but after about 30-45 seconds I hear a click comming from the glow plug relay(the black box on the driver side fender well). I have also tested to see if the plugs are getting voltage which they are. I just ordered the OEM glow plug relay from the MB dealer for $130, and the fuse as well for $.95(figured I'd get it just in case). I will be installing it tommorow morning and will post on how it goes.
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  #5  
Old 05-10-2005, 11:52 AM
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Stumped

Well, I installed the new glow plug relay today, check the resistance and voltage on the plugs and it was good, but it will still not start. I am stumped. I know the battery is good, the starter is about a month old, glow plugs are good, new glow plug relay. The next thing I believe I should check is to see if the fuel is getting to the injectors and the injectors are not clogged, but besides that any suggestions??
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  #6  
Old 05-10-2005, 11:59 AM
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Plugs

on my car replacing the plugs solved things with a 300cd 1983 that was difficult to start when cold. I kept the same relay.

See my other post about where to buy and how to put in the plugs
search "glow plug tip"

Mark
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  #7  
Old 05-10-2005, 12:13 PM
Old Deis
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After working through glow plug issues a few times on these old diesels, I have come to the conclusion that it takes less effort, less time, and is more certain to just pull the glow plugs out, clamp them into a vice, ground the vice and touch the end with a 12 v jumper cable. If the plug will not get hot fast, it needs to be replaced.
Usually when one of these quits starting either the third or the fourth glow plug just failed on your car, at that point it will take a lot of cranking, or a very good engine, or a very warm day to get it started.
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  #8  
Old 05-10-2005, 12:29 PM
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In an odd twist, I was out trying to figure what the heck was wrong and I turned the key the glow plug light came on for about 10 seconds, and went off, well I waited to start up to about 30 sec, and without moving the key the glow plug light came on again. Is this the glow plugs? am I best replacing them?
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  #9  
Old 05-10-2005, 12:58 PM
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Quote:
Originally Posted by mbenzgoodyear
Well, I installed the new glow plug relay today, check the resistance and voltage on the plugs and it was good, but it will still not start. I am stumped. I know the battery is good, the starter is about a month old, glow plugs are good, new glow plug relay. The next thing I believe I should check is to see if the fuel is getting to the injectors and the injectors are not clogged, but besides that any suggestions??
Well, the glow plug relay cannot be the culprit because you measured voltage at the glow plugs. So, it's ruled out (and could have been ruled out prior to purchasing a new one).

Please provide a detailed explanation of how you have concluded that the glow plugs are good.

When the dash light starts doing funny things, normally at least two glow plugs are not working properly.

I would not proceed to look at other reasons for failure to start until the glow plug system is functioning properly, and this includes a properly working indicator light.
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  #10  
Old 05-10-2005, 01:37 PM
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Well I did a few things. I took all the plugs out and connected the to a battery to see if they would get hot, and all five got hot quickly( not sure of the temp). Then according the the trusty haynes manual I hooked up the ohmmeter (set on 200) to the glow plug controller and checked for an infinity reading, which none had. I also checked voltage at the pins on the controller to be sure they were getting 12V when the key was turned on.

From what I can tell the indicator light had no problems, unless the plugs are shot. I just bought new glow plugs and am going to install them this afternoon. I have also inspected the wires going to all the glow plugs and they seem to be good, no exposed wires or cracks in plastic covers.

Also the old relay was not getting any power to it, so I tested the power lead to it and there was juice to it. I can only conlude that the relay itself was not working, as the fuse on it was good.

I will try to replace the glow plugs today, see if that helps Does this seem like the correct path to take, I believe it is from what I have read here on the forum?
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  #11  
Old 05-10-2005, 01:53 PM
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Quote:
Originally Posted by mbenzgoodyear
Well I did a few things. I took all the plugs out and connected the to a battery to see if they would get hot, and all five got hot quickly( not sure of the temp). Then according the the trusty haynes manual I hooked up the ohmmeter (set on 200) to the glow plug controller and checked for an infinity reading, which none had. I also checked voltage at the pins on the controller to be sure they were getting 12V when the key was turned on.

From what I can tell the indicator light had no problems, unless the plugs are shot. I just bought new glow plugs and am going to install them this afternoon. I have also inspected the wires going to all the glow plugs and they seem to be good, no exposed wires or cracks in plastic covers.

Also the old relay was not getting any power to it, so I tested the power lead to it and there was juice to it. I can only conlude that the relay itself was not working, as the fuse on it was good.

I will try to replace the glow plugs today, see if that helps Does this seem like the correct path to take, I believe it is from what I have read here on the forum?

Some things are making no sense.

You previously indicated that the glow plugs were getting 12V, prior to changing the relay. Now, you state that the old relay was not getting any power to it. These two statements contradict each other.

You previously indicated that the glow plug indicator light was not behaving correctly. Now, you state that the indicator light "had no problems". Was this observed after changing the glow plug relay?

The sequence of events is escaping me and without a clear and concise timeline of symptoms and events, we are going to get FUBAR, as Mr. Hunter would say.
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  #12  
Old 05-10-2005, 02:22 PM
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I apoligize for the confusion. Here is what I have done:

The car will not start.
-Glow Plug indicator on the dash does not come on, but after 30 seconds with the key on, I hear a click come from the glow plug relay.

-I test the resistance on the glow plus with my ohm meter, by disconnecting the glow plug connection at the realy, everything checks out ok.

-I also test the plugs for voltage, to see if they are getting juice. The voltage seems to be ok on all the plugs.(Done with GP still in).

-I take the plugs out, and test each one with a battery to see if they get hot, from what I can tell they are getting hot.

-With the plugs out, I test the realy to determine if it may be the cause.

-With the key turned, I hook up the mulitmeter to determine if it is getting power. Where the plug to the glow plus plugs in, I check each metal stud to see if they are getting power. Only one shows any indication that power is getting to it.

-I take off the power connector to the realy and test it, it does get power, so I conclude the relay is bad.

-I replace the relay and test it with the power connector connected, I get power on all the studs on the relay. Now the indicator lights up on the dash.

-I hook up the glow plugs and inspect the wires to make sure none are exposed, which none are nor there any cracks in the plastic covering them.

-I check the resistance again and they check out ok again.

-When I turn the key, the light comes on, for about 10 seconds and then goes off, so I try start and it cranks, but will not turn over.

-I take the key out, wait about 2 minutes, put the key back in, the light comes on for about 10 second then goes off, but if I wait for 20-30 seconds the light will come back on and doesnt go off(well at least for 3 minutes).

The only think that I can think is that maybe the plugs are not getting hot enough, or that one or more is bad. Oh yea, I also have check the fuse to make sure it is nothing as silly as that.

rderton sorry for hijacking your thread, if you in Round Rock PM me, we can meet up in Austin and grab a drink, talk some benz, lol
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Last edited by mbenzgoodyear; 05-10-2005 at 02:29 PM.
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  #13  
Old 05-10-2005, 02:34 PM
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As I have experience with old MB's only, forgive me if this part is not on the 85, but did anyone check the fuse? It is usually found inside the relay itself.
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  #14  
Old 05-10-2005, 02:39 PM
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Quote:
Originally Posted by mbenzgoodyear
... I also have check the fuse to make sure it is nothing as silly as that.
I should have been more specific. I check the fuse in the fuse box, on the firewall, as well as the 80A fuse within the realy itself, both were not blown.
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  #15  
Old 05-10-2005, 02:43 PM
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On mine the dash light stayed on like always. I still had voltage at the relay, my repair CD recommends to replace the relay. Before I spent that much I just wanted to get other thoughts.
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