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  #1  
Old 09-15-2008, 06:53 PM
Bob Albrecht's Avatar
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Location: Kennett Square, PA
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Is my Glow Plug Relay the Problem?

I have a 1991 350SD with <50K mi on the engine (tight).

For about a year my glow plug dash light would not come on before starting on rare occasions when the engine was hot. I didn't know what to think of it, but it didn't bother me.

About 2 months ago the glow plug dash light started to come on for 20 seconds every now and then while I was driving; wierd. I knew something was wrong, but stuck my head in the sand.

A week ago the glow plug light started not coming on before the engine starts. The engine would start, but it ran very rough for about 30 seconds and made some extra smoke. The glow plug dash light would come on _after_ the engine started for about 20 seconds, then go out.

I finally have to do something about this. Winter is coming. No glow plugs in the winter = no starting.

The glow plug repair guide on DieselGiant was very helpful. (http://dieselgiant.com/glowplugrepair.htm). All 6 glow plugs / wires test good with less than .3 OHM resistance. I tested the power to the relay and the power to each glow plug. Everything is OK, it seems. For some reason there is no 80amp fuse on my relay, it must be a newer model.

After putting the cover back on the GP relay and changing the fuel filters (because I was looking at them and it had been more than 12K mi) I cranked the engine to prime the fuel system. The glow plug dash light acted normally!

The engine has started 3 times now with the glow plug dash light acting normally and the engine staring cold with no rough idle. (Can't be the glow plugs, right?)

Glow plug problems don't get solved by changing the fuel filter. Opening the relay cover, disconnecting and reconnecting wires, must have made it start working, right? It must still be flaky, right? It is only a matter of time, don't you think?

Should I replace the glow plug relay, or is there something else I should look at?

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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside
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  #2  
Old 09-15-2008, 07:43 PM
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Location: Walnut Creek, CA & 1,150 miles S of Key West
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I suspect the alum strip in the relay was corroruded and your messing with everything "fixed" it.

I'd leave well enough alone. Its worked for how long already?
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09' E320 Bluetec 77k
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  #3  
Old 09-15-2008, 08:23 PM
Bob Albrecht's Avatar
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No aluminum strip (80amp fuse)

Quote:
Originally Posted by TMAllison View Post
I suspect the alum strip in the relay was corroruded and your messing with everything "fixed" it.

I'd leave well enough alone. Its worked for how long already?
There is no aluminum strip. This relay does not have one. It must be something else.
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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside
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  #4  
Old 09-15-2008, 08:29 PM
F18 F18 is offline
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ditto....probably some corroded/dirty contact in the relay plug/glow plug harness or terminals on the relay. The next time it does it pull the plug from the relay and give the plug & terminals a shot of electronic cleaner or MAF sensor cleaner to remove any oily film and dirt....let it dry before assembly and try starting again.
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Daily Driver: 98 E300TD 199K
Hobby Car: 69 Austin Mini
Past Diesels: 84 300SD, 312K
87 300SDL, 251K
94 Chev. K-1500 6.5Ltr.TD, 373K
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  #5  
Old 09-15-2008, 08:49 PM
compress ignite's Avatar
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Dielectric Grease

1.Clean and dry all connections, as suggested earlier.
2.Apply a "Smidgen" of the WD40 (You don't want it "Dripping")to all the
contact points.
[I just picked the picture off the Internet...
I've got a toothpaste sized tube from Advance that I use on anything I can't
spray with Boeshield (T-9).]

Your Pre-Glow Relay does not have the 80 Amp fuse setup,
because it's protected ELECTRONICALLY (Too much "JUICE" and it disengages)
Some of the 124.128s have the same relay[And apparently mine has worked for
18 years...that's if it EVER was subjected to an OverAmp situation...(No Way to
tell)]
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Last edited by compress ignite; 07-15-2009 at 10:34 PM.
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  #6  
Old 09-15-2008, 10:12 PM
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The contacts looked very clean.

Quote:
Originally Posted by F18 View Post
ditto....probably some corroded/dirty contact in the relay plug/glow plug harness or terminals on the relay. The next time it does it pull the plug from the relay and give the plug & terminals a shot of electronic cleaner or MAF sensor cleaner to remove any oily film and dirt....let it dry before assembly and try starting again.
Hmm, the contacts looked very clean, but they are aluminum and invisible oxidation could have been preventing a good connection. I still suspect some bad contacts inside the relay, but who can tell? The next time it happens I will just tap on the side of it and see if that works.

Intermittent problems are very irritating.

P.S. My back window stuck down when I was test driving after the fuel filter change. Grrr.
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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside
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  #7  
Old 09-16-2008, 01:36 AM
compress ignite's Avatar
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Location: 32(degrees) North by 81(degrees) West
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Dielectric

The WD40 "HELPS" the two parts of the contact(PLUG or ETC.) maintain
Electrical continuity.

(Bad Analogy...But...Don't grab that 110 Volt Positive Wire UNTIL you are in
your bare feet standing in water! The H2O "HELPS" the contact...Just like the
WD40 "HELPS" the contact)

Do a an "Advanced Search" someone has posted pictures of the inside of the
GP Relay as he Re-Soldered it.

Also,it's no big task to test the GP Relay's output with a DMM at the Plug
Terminals on top of the Relay.('Tell you if it is, indeed, the problem)
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124.128

Last edited by compress ignite; 07-15-2009 at 10:35 PM.
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  #8  
Old 09-16-2008, 03:11 AM
Bob Albrecht's Avatar
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Location: Kennett Square, PA
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Already tested relay

I tested the relay per the DieselGiant instructions. It acted goofy at first, then seemed like it was working.

I can't think of anything except that it is messed-up inside. I can't believe that 6 contacts were bad when they looked perfect.

If it acts up again I am going to replace it.

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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside
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