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  #1  
Old 01-12-2010, 09:00 AM
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Location: chicago area, illinois
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glowplug light comes on randomly

i had my car plugged in last night and i went out and started it this morning; it started right up but after about 5 min of riving the glowplug light came back on and stayed on for like a min then went off. then after about 3 mins it came on again and i looked at the volt gauge i have installed and i could tell that the glowplugs were def being lit up and when the light went off the voltage went back to normal. im going to let it sit outside for a little bit and go try it out again but does anyone have any idea why this would happen?

thanks- J

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1985 mercedes benz 300D turbo diesel
1998 VW GTI VR6
1996 VW GTI 2.0
1999 saab 9-3 turbo
1987 300sdl (sold)
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  #2  
Old 01-12-2010, 10:28 AM
92 300D 2.5L OBK #59
 
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sounds like a bad glow plug. If you do a search you should find the info you need.
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  #3  
Old 01-12-2010, 11:12 AM
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I was under the impression that the glowplug light coming on as an indicator of a bad plug occurred immediately upon release of the starter and not minutes later.
Does anyone know if the 'glow plug light on as indicator of bad plug system' means that the glow plugs are actually energized when the light comes on? I had assumed that only the light was coming on and that the glow plugs were not being energized.
There have been a number of instances reported on here of glow plug relay's sticking on after the timer should have turned them off but I don't recall another instance of a relay randomly energizing in the manner your report. But then on other other hand, few people have a voltmeter that would tell them that a random glow plug light appearance meant the glow plugs were actually being energized as opposed to just the light flashing on. I'd hypothesize a problem in the ignition switch but that's just a random shot.
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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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  #4  
Old 01-12-2010, 11:32 AM
Craig
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I once had my indicator light coming on randomly while driving, but I don't know of the GPs were actually coming on. I fixed it by replacing the relay.
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  #5  
Old 01-12-2010, 11:45 AM
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Originally Posted by TurboSDL View Post
...does anyone have any idea why this would happen?
Any interruption in "run" power (as would be caused by a loose connection) will have the same affect as turning the key off and back on. The glow sequence will be initiated any time power is restored.
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  #6  
Old 01-12-2010, 12:09 PM
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I had this happen to me last year. My light would blink on randomly while driving. I have concluded that the GP relay was bad. Around the same time I was also having charging issues with alternators going bad. Since I replaced the GP relay with one from Fastlane I have not had any issues.

My conclusion was that the relay would come on and stay on and took out my alternators. I'm not 100% certain but it has been about 6 months and none of the symptoms have come back so it seems that a new GP relay did indeed solve the issue.
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  #7  
Old 01-12-2010, 12:46 PM
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well its still acting up.... it went like 10 min without coming on then sometimes the light comes on for like 30 seconds sometimes for like 5 seconds then off then back on again for a couple seconds, its weird but when the light comes on the glow plugs are DEFINITELY glowing because my voltage gauge drops down to abt 12.6 volts when its usually at about 14.2 volts when the car is cruising. when i was in the driveway tho, i was sitting there waiting for the light to go off before i shut down the car. it went off but the voltmeter didnt go back to 14.2 volts for like another 10 15 seconds after the light was off. i also heard a kinda loud click coming from the relay area, im guessing it was just shutting off the plugs but it seems like u shouldnt be able to hear the relay shutting them off.... maybe i just never noticed it before.

i also checked the wires to the glowplugs and they were all tight.
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1998 VW GTI VR6
1996 VW GTI 2.0
1999 saab 9-3 turbo
1987 300sdl (sold)
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  #8  
Old 01-12-2010, 01:09 PM
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Quote:
Originally Posted by TurboSDL View Post
well its still acting up.... it went like 10 min without coming on then sometimes the light comes on for like 30 seconds sometimes for like 5 seconds then off then back on again for a couple seconds, its weird but when the light comes on the glow plugs are DEFINITELY glowing because my voltage gauge drops down to abt 12.6 volts when its usually at about 14.2 volts when the car is cruising. when i was in the driveway tho, i was sitting there waiting for the light to go off before i shut down the car. it went off but the voltmeter didnt go back to 14.2 volts for like another 10 15 seconds after the light was off. i also heard a kinda loud click coming from the relay area, im guessing it was just shutting off the plugs but it seems like u shouldnt be able to hear the relay shutting them off.... maybe i just never noticed it before.

i also checked the wires to the glowplugs and they were all tight.
I would say you need a new glow plug relay. Mine made a hissing noise when I turned the car off. I wasn't even able to regularly see the voltage changes like you did but I was still pretty certain it was the relay. If you notice the voltage changes I would be very confident in saying you need a new one.

Order it from Phil. You can get the new afterglow ones with 4 duratherm GPs for like $116.

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1984@@1984&makeid=63@@MERCEDES+BENZ@@X&modelid=6208%3AMBC%7C1510%3AED%7C10000134@@300SD&keyword=relay@@relay&catid=All@@All&subcatid=P%3A242005@@Preglow+Time+Relay&applicationid=W0133-1606169&mode=PA

I am going to the pick n pull (hopefully) today. They have an 84 300D. I'll see how much they want for the GP relay so I may have a spare. But if I were you I would just order a new one from Phil ASAP.
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2004 E320 Wagon

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD
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  #9  
Old 01-12-2010, 01:10 PM
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Quote:
Originally Posted by TurboSDL View Post
...it seems like u shouldnt be able to hear the relay shutting them off...
Why would it seem that way? Big relay, big spring, big clunk.

Quote:
Originally Posted by TurboSDL View Post
i also checked the wires to the glowplugs and they were all tight.
You need too focus on the circuit between the ignition switch and the relay assembly, especially the black/red wire. If there is no problem there, you probably have a bad connection internal to the relay assembly.
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  #10  
Old 01-12-2010, 01:14 PM
Craig
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That's the kit I have in the 300D. It works great with one word of caution; if you make lots of very short trips it will tend to allow your battery to run down. The 65W alternator has trouble keeping up with the glow plugs and charging the battery at the same time (especially at night). My 300D normally takes very long trips so it's not an issue. However, I have a standard relay in the 240D because it normally get used around town (and it never goes outside in the cold anyway).
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  #11  
Old 01-12-2010, 01:18 PM
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Quote:
Originally Posted by Craig View Post
That's the kit I have in the 300D. It works great with one word of caution; if you make lots of very short trips it will tend to allow your battery to run down. The 65W alternator has trouble keeping up with the glow plugs and charging the battery at the same time (especially at night). My 300D normally takes very long trips so it's not an issue. However, I have a standard relay in the 240D because it normally get used around town (and it never goes outside in the cold anyway).
Excellent point. I have a higher amp aftermarket alternator so I don't worry about it as much. But if I start the car in the cold to just move it around my driveway, I do notice the battery is drained a bit because the starter may spin a bit slower upon the next start up.
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2004 E320 Wagon

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD
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  #12  
Old 01-12-2010, 01:21 PM
Craig
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Originally Posted by Graplr View Post
Excellent point. I have a higher amp aftermarket alternator so I don't worry about it as much. But if I start the car in the cold to just move it around my driveway, I do notice the battery is drained a bit because the starter may spin a bit slower upon the next start up.
Yup, I actually had to put mine on the charger last week after I made a bunch of short trips only over a couple of days in cold weather. I noticed the starter was starting to slow down after about a dozen starts. Just something to be aware of.
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  #13  
Old 01-12-2010, 06:49 PM
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when my 1995 E300 did this, it needed a new GP wiring harness......

all better now! I also replaced the GP, one was bad
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  #14  
Old 01-12-2010, 11:10 PM
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I had the same problem 6 weeks ago. I found a relay at the junkyard and it solved the problem. Your current relay is probably sticking.
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  #15  
Old 01-12-2010, 11:12 PM
92 300D 2.5L OBK #59
 
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Have you removed/cleaned the contacts and reinstalled the relay?

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