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68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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4,163 Posts
ABS has nothing to do with ignition. REcap: replace cap and rotor with genuine Bosch parts. Report back if there is still a problem later. *you are correct that many MB parts counters dont know anything.
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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39,395 Posts
it is the distributor distribution rotor. I have never seen this before. I am sending pics. If you have a moment to give Me a call at 850 543 3102. I will give you every thing I have done. NEED HELP. I AM A HIGH PERFORMANCE MERCURY MACHANIC BUT CAN'T FIGURE THIS ONE OUT.
I had this issue a number of years ago and went through a number of ignition rotors, also replaced wire set with new BERU, Bosch W9DCO plugs, new OE distributor caps etc.
We finally located the culprit as a worn snail/worm gear inside the engine, the one that the gear of the distributor goes into. It was a pretty big job, but as we replaced the upper and lower chain guides, chains,and sprockets, incl rebuild oil pump anyhow, it wasn't that much more work.
The gear wasn't cheap, but for any part inside the engine I would go original MB only (if not NLA?)
Hopefully, in your case it's something less involved, perhaps just be the quality of the par?.
What brand were distributor cap and rotor? Imo, they should be changed together.

In case you didn't know, one of the stickies on top has the Mercedes Benz USA = MBUSA W126 service manual (requires adobe flash) https://www.startekinfo.com/StarTek/outside/12253/?requestedDocId=12253

If you don't have access to the MB parts catalog, online seller autohausaz uses the original parts numbers you can search with, and a good number of vendors sell original Mercedes parts at a discount, with free ground (UPS, FedEx) shipping for orders over $49 or so.
 

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1990 420 SEC
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106 Posts
How much end play does the distributor have? I found on my car today a broken thrust washer on top of the driving gear of distributor. Without the pieces in place there is a plenty of endplay. Same effect as worn gear I quess.
 

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Discussion Starter #24
Here are a few things I have checked over the week end. I have 14.98 volts at the hot side of the coil. That seems to be high to Me. Also the relay with the fuse, is a 5 post relay and on my 1985 500sec and the 380se there are only 4 female insert sockets, is this correct? Also could the chain jump Timing on the cam? I under stand that the system is different the high performance motors operate at high voltage when running. But what about the old systems?

AND TO EVERY ONE OUT THIER THANK YOU FOR YOUR INPUT!!!!!!!!!!!!!!!!!!
 

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Discussion Starter #25
If you look on the Mercedes source website He has a video that He replaced about every thing in the fuel system, but the car would not run correctly. Found that the speed control sensors were full of rust. He cleaned them and the problem was solved. This is the only reason I said this.
 

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1st , the voltage at the coil is correct . Second , stop buying Beru ignition parts . They have been known for years to be rubbish especially the woeful rotors and caps . Use only Bosch .
 

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1985 380SE IHAVE REPLACED ALMOST ALL THE INGNITION PARTS AND THE CAR WILL BURN THROUGH THE ROTOR BUTTON IN A VERY SHORT TIME. ANY ONE SEE THIS BEFORE?
Make sure the carbon button and spring are still in the cap ,if they were missing there would be arcing to the rotor .
Check coil for correct voltage ,it may have been replaced by a ballast resistor type .
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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39,395 Posts
1st , the voltage at the coil is correct . Second , stop buying Beru ignition parts . They have been known for years to be rubbish especially the woeful rotors and caps . Use only Bosch .
Wow, Beru used to be the gold standard in Germany. I heard they have been bought by a multinational not log ago..
A few years back, we had a new Bosch wire set straight out of the box, where resistance was already all over the place. I am German and it pains me to say that.about Bosch. In my own experience, comparing online bought and same brand bought from the dealer parts can be of different quality. (I once bought from different sellers, 2 sets of elring head haskets sets fir o.k. but not good enough for old time MB mechanic, Jerry RIP, but the same brand elring set sourced from the Mercedes dealer fit perfect).
As far as rotor and distr cap go, i agree with you.
I had good experiences with wire sets from direct seller Kingsborne, San Marcos, CA, and Karlyn STI.
Cheers
 

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1986/1990 W126
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13,378 Posts
Mercedes Bosch is a different animal to the standard Bosch. It's lovely quality still, but who can afford it. For myself I'd rather save and buy that, than cheaper lesser quality.

I didn't know, but someone had fitted Chinese rotor arm too my 420se prior to my ownership. It was fine for ages until the car glided gracefully to a halt from the overtaking lane on the highway. Rotor arm had literally melted and turned into something like spun sugar strands!
The MB replacement wasn't cheap, but I don't imagine I'll have to replace it ever again.
 

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Discussion Starter #30
The voltage is high? What should it read on the positive side of the coil when it is idol speed? This seems to be the problem of burning the end of the rotor button?
 

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2008 AMG CLK63 Conv., 2012 R350 4-Matic, Wife's 2015 C300 sedan
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Have you tried replacing the condenser in the distributor?
 
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