PeachParts Mercedes-Benz Forum - Diagnosing Glow Controller Problem

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Quote:

Originally Posted by compress ignite (Post 2463670)

EDIT: Just so all of this won't be "All Fun,All the Time"...
Physically locate the separate "Ground" wire for the Electronic Pre-Glow Relay
at it's terminus on the body.
And assure yourself the Connections and the Cable are good.
An intermittent Grounding Connection sounds awfully like your symptoms, TOO
(I admit I'm grabbing at non-existent Life Rings, here.)
BUT, maybe, each time you R+R the Relay to clean the contacts / you also
"Fix" a Ground problem,Temporarily.

1992 is awfully close to the "Middle Nineties"
"Automatic Self (Ecologically) Degrading Engine Wiring Harnesses"
Mercedes bought from a Vendor and "Gifted" [Spelled, F**ked] some owners with.

(Recycling was all the rage in Deutschland, and the Vendor screwed up on the insulation specifications. OR MAYBE NOT?!?)

I'd clean the contactor(s) once more and make sure they're super duper SHINY and Smooth/Mirror Like and then apply Stabilant22 to both sides.
(It's about $30.00 for 5Ml which makes 15Ml solution)

[OUTRAGEOUS! But the stuff works.]

And it's cheaper than a New GP Relay.

http://www.stabilant.com/techt02h.htm
http://www.stabilant.com/sizes01h.htm

Example of pricing:http://www.posthorn.com/Stab_2.html

I'll clean it again....and again even if I need to use this car. I'll take a look around and find the ground for the unit and see if there's a problem, which I suppose there might be since this car was "worked on" by someone during the last five years that didn't seem to know what they were doing or didn't care.

The contacts are clean, that's what bothers me, I don't really do much to it before I put it back in, and then it works, so perhaps the ground might be a problem.

As for harness degradation, I was led to believe that the 92 escaped that terrible self-destructive sheathing problem. My harness, what there is of it under the hood, which isn't much, looks to be in very fine shape insulation wise so I'm hoping that this isn't an issue.

Thanks
Steve A

Well I pulled and cleaned it again, and checked the wiring to the controller and back into the harness itself and I found no problems.

It worked once and then failed again.

Any other advice on this before I just replace it. I hate to replace it, especially without being able to do any more diagnostic work on it but I feel as though I have little choice.

Thanks
Steve A

Wire for Terminal #31 (In the 5 pin plug) is GROUND

1.You have a GP Relay that's working erratically.
2.You will Not Be Happy ,If you "Plug In" a New GP Relay and get same results.

Find the wire/pin labeled 31 on the five pin plug AND Trace It to it's TERMINATION on the Chassis. Disconnect it at the Termination and Test it for BOTH Resistance and CONTINUITY.Check the Termination Point for:
Clean and Bright.

(Unsolicited Personal Comment: If T'were me I'd be testing ALL the Wiring in the Glow Harness for "R" and "C" before I'd FORK over the cost of a New Relay.)

[The reason I'm so adamant about this Ground Wire is someone else "Fixed" all
of his GP Relay problems by rectifying the Ground problem.]

(Please ignore the Black Arrow in the Pictogram , it is simply pointing to the
"Always Hot" pin on the GP Relay)

I had an intermittent problem like this. I could reach under the hood and press the relay cover and get the relay to click, which told me it was the plug on the relay. I had stacked the two harnesses under the relay cover in the wrong order, which left the top one loose on its pins. Pushing on the cover made it work.

Later it failed to light up immediately, choosing to make me wait with key on for longer and longer periods for the glow light to come on. That proved to be a badly chafed main voltage wire, easily fixed.

My point is that at this age, the terminals and general conditon of the wiring harnesses are always suspect and should be carefully cleaned and lubed with contact paste every time you look under the hood.

Thank you for the advice guys, I believe we're on the right track now.

I drove the car yesterday and as I mentioned the controller failed after one use. I went out last night to fiddle with it and pulled the unit, still connected, from the case and set the assembly aside and watched it physically work. I could not get it to fail in that position.

I went out this morning, no glow. I unbolted the unit from the mountings and repositioned it vertically and it worked, so the problem isn't inside the unit, it's probably the contacts in the connectors or perhaps the ground.

At any rate progress has been made.

Thanks
Steve A

(Hopefully)

I had an old Volvo back in the middle seventies ,that I refused to put a new
part on without definitive diagnostics.One morning I got a Telegram from the
chassis stating,"Bad Spark Plug Wire on Number Two".