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  #1  
Old 08-07-2005, 06:17 PM
Eck Eck is offline
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Join Date: Aug 2005
Posts: 1
W126 Start Problems - PreGlow Relay?

Hey Guys and Gals-

Bruno ('87 SDL, 251K) and I are new to the list. My M126 repair CDs don't seem to like my new computer, so I'm in the dark troubleshooting my latest problem.

Bruno's Glow Plug light doesn't come on when I turn the key to the "glow" position, and cranking does no good - so I'm thinking the glow plugs aren't getting any juice. I checked all of the fuses, fusible links etc. I could find, nothing obviously wrong.

The relay in my ameteur's mind seems like the likely candidate, but since it's an expensive part, I'd like to make sure . . . .

Can anyone help me out here?

Thanks in Advance!

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  #2  
Old 08-07-2005, 06:44 PM
Geezer
 
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
Quote:
Originally Posted by Eck
...Bruno's Glow Plug light doesn't come on when I turn the key to the "glow" position, and cranking does no good - so I'm thinking the glow plugs aren't getting any juice. I checked all of the fuses, fusible links etc. I could find, nothing obviously wrong.
First, welcome!

The Glow Plug (GP) light generally will not function if two or more GPs are open or burned out. However, your OM603 engine should still start with two, or more, burned out. Be sure to wait at least 15-20 seconds after turning the key for maximum glow effect of the remaining glow plugs. (I usually wait for the seatbelt buzzer to stop. ) It should then start, but might be 'lumpy and grumpy' for a while.

To test the GPs, find the relay box, driver's side, low in front of fender. Remove the plastic cap, it just snaps off.

Under the cap, you will see two connectors. Remove the six-wire connector (applies power to GP 1-6) and use a multi-meter to read resistance from chassis ground to each GP at the connector. Somewhere in the vicinity of 1.0 ohm is usually OK. Infinite is 'open' or burned out, and 0.0 is shorted, which is also bad. The connector has numbers next to each socket, make a note of which number reads 'bad' and plan to replace at least that GP or GPs. Oh, and cylinder #1 is at the front, #6 at the rear.

On the relay box is a thin strip of metal under a pair of Phillips screws. This is actually an 80A fuse strip. It is not common for this to melt, but it may have if a GP has shorted.

Good luck, and let us know what you find.

If you use the "Search" feature in the menu bar above, "Glow plugs" will net you a lot more information and reading.

Best Regards,
Jim
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  #3  
Old 08-19-2005, 09:52 PM
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Join Date: Aug 2005
Posts: 22
Hey Jim,

I tried searching around for some clues on Glow Plugs..got a lot of information, but none that seemed to address my specific concern:

I inherited the 84 300SD from my dad, who said about 2 years ago, the glow plugs got changed. My plugs indicator light works about 1 out of 10 tries, other than that, its just been really grumpy on cranking and I don't know why.

Are fuses tied to glowplugs in some way? I think I'm long overdue for changing out the fuses, so I'm interested in whether or not this will help the plugs.

Again, sorry if this question has already been addressed someplace else on this board. I DID try searching!
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  #4  
Old 08-19-2005, 10:11 PM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,166
Quote:
Originally Posted by Large_Crab
........ My plugs indicator light works about 1 out of 10 tries, other than that, its just been really grumpy on cranking and I don't know why. .........
Sounds like the plugs may be a little carboned up or a loose connection, maybe at one of the plugs. There is a glow plug reamer that is available at Performance Products, Samstagsales and I believe **************.

When were the valves adjusted last?
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84 300SD 350K+ miles ( Blue Belle )
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  #5  
Old 08-20-2005, 06:44 AM
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Join Date: Aug 2005
Posts: 22
Quote:
Originally Posted by SD Blue
Sounds like the plugs may be a little carboned up or a loose connection, maybe at one of the plugs. There is a glow plug reamer that is available at Performance Products, Samstagsales and I believe **************.

When were the valves adjusted last?
I'll check that out, thanks.

I'm not sure when the valves were adjusted...hell, I'm a MBZ newb, so I don't even know what you're talking about! lol
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  #6  
Old 08-20-2005, 10:15 AM
Geezer
 
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
Quote:
Originally Posted by Large_Crab
I inherited the 84 300SD from my dad, who said about 2 years ago, the glow plugs got changed. My plugs indicator light works about 1 out of 10 tries, other than that, its just been really grumpy on cranking and I don't know why...
Grumpy starting AND indicator not working usually means 2 or more GPs are not functioning. They do eventually burn out, and it sounds like you are not quite sure how old yours are...

Go ahead, take 5-10 minutes and check each GP for resistance as I described.

I also found that when my lamp would not light up with known good GPs, there was some corrosion some of the sockets of the 6-pin GP wiring harness connector. My connector has 6 sockets, you will have 5 and a 'blank.' Take a good a look, and if you see some white or green fluffy, powdery substance, spray in some good contact cleaner (NOT WD-40!) and clean up the socket. Corrosion can add enough resistance to make the system act like a GP is burned out, but make good contact once in a while.

Quote:
Originally Posted by Large_Crab
...Are fuses tied to glowplugs in some way? I think I'm long overdue for changing out the fuses, so I'm interested in whether or not this will help the plugs.
The fuses you are thinking about are not involved. There is an 80A strip fuse for the GP relay itself. It is flat and held by two phillips screws, and if it cracks or melts, none of the GPs will EVER come on.

If this fuse is gone, you will get REALLY grumpy starting, or no starting at all! The strip fuse does not need not need to be cleaned or rotated like the barrel fuses.

Quote:
Originally Posted by Large_Crab
...Again, sorry if this question has already been addressed someplace else on this board. I DID try searching!
Thank you for searching. The Search feature is a bit limited, and a lot of the information is contained 'off topic' in an unrelated thread, or buried pretty well.

Let us know what you find.

Best Regards,
Jim
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  #7  
Old 08-20-2005, 10:29 AM
Geezer
 
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
Quote:
Originally Posted by Large_Crab
...I'm not sure when the valves were adjusted...hell, I'm a MBZ newb, so I don't even know what you're talking about! lol
Most engines that have hydraulically actuated self-adjusting valve actuators and do not need adjustment. The actuators on your engine are mechanical and need to be checked at set at regular (15,000 miles or so) intervals.

As the valve and adjuster wear over time, the adjuster clearance gets smaller. Beyond this point when there is no more clearance, further wear means that the valve cannot close completely and will begin to leak. When this happens you lose compression, and the engine may not run as well and can be harder to start.

There are a LOT of threads on checking and adjusting valves. Try a Search, and let us know.

Best Regards,
Jim
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  #8  
Old 08-20-2005, 12:12 PM
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Join Date: Jun 2005
Location: San Jose, CA
Posts: 160
I had troble starting my 81 300SD (OM 617) til i got a valve adjustment done on it and also i let the glow plugs cycle completely by waiting for the seatbelt buzzer to go off and i tap the fuel accelorator a few times. now after the adjustment and letting the GP cycle starts in half a compression stroke (well maybe not that fast but pretty darn quick.)

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