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  #1  
Old 05-08-2011, 10:17 PM
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76 W115 300D, won't start, glow plug light permiently on

I checked and I have power from the wire going to cyl # 5 glow plug so I assume that the relay is fine. Does this sound correct?

If so then i'll replace the offending glow plug tomorrow. It looks older then all of the others.

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  #2  
Old 05-08-2011, 10:30 PM
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Yes. It could be another plug that is bad. You can check them by testing continuity thru the loop by using an ohmeter on the two connection points on each plug without removing them. Could also be a bad ground.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #3  
Old 05-09-2011, 08:02 PM
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OK So I replaced the glow plug on cyl number 5 and the end was split wide in the same way that you would see a burnt out fuse. I replaced it and nothing changed. I think that i may have a ground somewhere.

Any idea what needs to be checked?
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Old 05-09-2011, 08:51 PM
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how are other 4 gps? make sure the temp switch ground wire is connected.
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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Old 05-09-2011, 08:58 PM
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I have not pulled it. The system seems to be blowing glow plugs. I pulled the new one and sure enough, the plug was blown. I put another one (old on sitting in the trunk) and it went in about 10 seconds. It looks like i'm getting a lot of current going to the glow plug. I would have expected the relay to fuse to blow before the glow plug to go.

I had a short on my radio this weekend which i resolved and capped off a lot of the loose wires under the dash. I wonder if I did something that that is resulting in the glow plugs getting too much current?
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Old 05-09-2011, 09:01 PM
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sounds like a bad relay. The GP's do not have a fuse. The is a OVP inside the GP relay which will trip and cut power when to much is drawn.
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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  #7  
Old 05-09-2011, 09:01 PM
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Where is the relay?
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Old 05-09-2011, 09:05 PM
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Drivers side under dash, bolted to the steering column support. 7 pins... its tucked up there pretty good so just look for a silver box.
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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  #9  
Old 05-09-2011, 09:07 PM
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Quote:
Originally Posted by 79Mercy View Post
Drivers side under dash, bolted to the steering column support. 7 pins... its tucked up there pretty good so just look for a silver box.
Of course Worldpac shows it as NLA. I'm surprised that it would be the relay given that there is power to the glow plug.
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  #10  
Old 05-09-2011, 09:47 PM
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I don't think your plugs can be getting too much current. They can only get 12 volts. But all the plugs need to be hooked together in a series so that the voltage to each one is appropriate. I'm guessing that number 4 plug is grounded out and and a result number 5 is getting too much power. Or maybe it's number 3.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #11  
Old 05-09-2011, 10:03 PM
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Quote:
Originally Posted by 79Mercy View Post
The is a OVP inside the GP relay which will trip and cut power when to much is drawn.
Didn't know that, interesting they were doing that back in 75. I guess that's what that bimetallic stip in the glass capsule is for?

As I understand it the relay does not control the timing of the glow plugs, it just clicks on for some time (120 sec?) until you start the car, and also clicks on while cranking. There is a thermo-time switch on the head which the glow plugs ground to. That is what switches the plugs (and dashboard indicator).

Last winter I had seen the relay was available on german ebay.

-J
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  #12  
Old 05-09-2011, 11:00 PM
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OK I'm ordering 5 new glow plugs and i'm going to replace them all. If that does not work, I may upgrade to the new type plugs which have their own relay.
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  #13  
Old 05-09-2011, 11:05 PM
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Double check the wiring. If the insulators are not in the right place I think it's possible that current can bypass some glowplugs putting too much voltage to the first one.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #14  
Old 05-09-2011, 11:47 PM
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I'm having this problem too. My car will start. I just count to 40.
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  #15  
Old 05-09-2011, 11:48 PM
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Thanks guys, I'll order a full set of glow plugs tomorrow.

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