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1998 SL500 Sport
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Discussion Starter #1
Climbing down the wormhole but thought I'd post to see if there might be something I haven't thought of. 1995 E420, 171,000 miles, out for a drive for approx. 15 minutes when the car suddenly felt like it was running on 4 or 6 cylinders. Felt similar to a caps failure but they're 3 mo. old so I ruled them out. Limped the car home and replaced all the plugs. Same issue. (no CEL) ran the codes anyway and the DM showed an ignition failure on bank 1 so I went down the train and replaced the Ignition coils. Same problem. Next down the line, replaced the EZL. Again, same issue. This time though the car threw a CEL and SRS light. Tried running the codes through Xentry and showed the DM as clear of faults. Also, the onboard diagnostic module holds the red LED when pressed and nothing after. Replaced the fuel filter and confirmed fuel pumps are good. Pressure regulator was replaced last year so that's good.

Live data shows proper voltage to MAF, O2 and ignition is stable at 30v / cylinder so it's not an ignition issue as far as I can tell. Based on the fact that the DM is unresponsive am thinking there's a wiring issue but the main harness has already been replaced with updated wiring and looks good. Lower harness is original but don't know if that might be the culprit considering it isn't controlling much outside of the the starter and alternator.

Car smells running rich but no rotten egg smell so I don't think the cats are bad.

Pretty much stuck at this point so if anyone has any insights let me know.

Thanks in advance!
 

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W124
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You need to change the dust shields (insulators) behind the rotors. Happened to me not two weeks ago. Had one bank go absolutely dead after fifteen minutes running. New caps, rotors, and insulators and she runs perfectly again.
 

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1998 SL500 Sport
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Discussion Starter #3
If the insulators are bad won't there be ignition voltage issues at the cylinders? I've replaced the caps and rotors probably 5 times over the life of the car and this stumble seems different from a caps/ignition failure. When running the engine shows steady 28 - 31V per cylinder which seems normal. I'll look at the insulator caps today. Thanks!
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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The primary purpose for the insulators are noise suppression. As with electronics, noise causes all sorts of odd behavior. The insulators are a often overlooked item, and based on the age of these cars even the garage queens are in need of fresh ignition systems.
 

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1995 E-420
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Pull your rotors and the rotor mounts then pull the insulators. Bet the back of them will be wet with a weird jell if so cleaning them will help for a little while but it will come back they will need to be replaced. My 95 E 420 had exactly this same problem a new set of Bosh Insulators caps and rotors cured the issue.
 

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W124
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I have a feeling that insulators (although essential to replace for these problems) will fail prematurely if the seal behind them is not changed. That "gel" is probably a mixture of moisture and oil seeping past the seal.
 

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1995 E-420
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I have a feeling that insulators (although essential to replace for these problems) will fail prematurely if the seal behind them is not changed. That "gel" is probably a mixture of moisture and oil seeping past the seal.
Not one drop of oil leaking into my insulators from the cam solenoids on my car it was bone dry behind the insulators on oil. The jell was cleaned off twice and returned on the rear of the insulators. The issue vanished after I replaced the insulator it has some thing to do with the breakdown of the material over time in the insulators. Owned my car and been using it as a daily driver for almost 8 years now.
The front of the insulators was dry you only saw the issue when you pulled the rotor mounts and flipped the insulators over as front was dry and back wet. This issue will play havoc with these ignition systems in particular in environments where there is a lot of moisture in the air.
I do almost all of my work on the E 420 and trust me after daily driving a 95 O34 for almost 8 years know these cars pretty well. This issue is discussed at length over on the E500 board as all of us there have dealt with this monster!
 

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I just had my distributor caps and rotors replaced to get a newly purchased car running properly. The shop said when they pulled the old ones, the housings were filled with water so they put silicone on the new ones to try and prevent this. I also noticed after I bought the car that this was the second time in a year or two that the distributors had been replaced. I doubt the shop went as far as replacing these insulators you are talking about so I was thinking about possibly doing this soon to protect the new distributors but I looked up the parts diagram and don't see any "insulators" that you are talking about here M 119.975 - IGNITION SYSTEM > Mercedes EPC Online > nemigaparts.com
How would I go about ordering these and where are they located exactly?
 

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Or should I just see how it goes and hope the sealant they put on will be sufficient to make the caps and rotors work reliably for a while?
 

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W124
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Mercedes calls them dust shields rather than insulators. If you have water in the distributors, something odd is happening. Normally, with good caps, cap shrouds, and new o rings on the dust shield, there shouldn't be a significant amount of water/moisture in there. There is no reason to seal up the caps.
 

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Ok good the previous owner used a questionable shop to install the previous ones so who knows what was done exactly
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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And for best long term durability use original MB parts. The Bosch parts sold in the aftermarket are not up to the same level as the original stuff.
 

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Wow, the Bosch branded distributor is $85.49 compared to $216.20 for Genuine Mercedes........I hear you though that some "OEM" parts are not the same quality as genuine....
 

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Wow, the Bosch branded distributor is $85.49 compared to $216.20 for Genuine Mercedes........I hear you though that some "OEM" parts are not the same quality as genuine....
Yeah, this is why Mercedes is losing my business. You can buy three "substandard" caps for nearly the same amount as one "Genuine". The labor to change them isn't a big deal so why overpay in this case? The Genuines don't last three times longer as far as I can tell.

Oh and the stake in the heart of the Genuine cap is that FCP Euro warrantees the parts they sell for the life of the car.
 

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2003 G500, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Someone told me that the MB parts division is supposed to be a profit center at MB. I'm not sure if this is true or not, but it certainly would help explain the grossly exorbitant prices and the lack of support for less common, older parts.
 

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Someone told me that the MB parts division is supposed to be a profit center at MB. I'm not sure if this is true or not, but it certainly would help explain the grossly exorbitant prices and the lack of support for less common, older parts.
Yes, it certainly could be a profit center. The steep price differential indicates there could be more at play.

Its customary in a manufacturer/dealer business model for the entire service support arm of the company to be charged against the replacement parts division. This means the regional Manufacturer's reps who call on dealer service departments, the entire service training effort, the technical support help desk, and the service parts operation all would be under the same budget and living off the same "profit dollars"

Add the pressure of increased competition for the parts business and the situation starts getting serious. Marketshare lost to third party parts suppliers such as Uro and others, as well as equivalent quality parts being sold "out the back door" of the Genuine suppliers, leaves the manufacturer with few options other than cutting service support expense or raising parts prices

And yes, reducing the size of the warehouses, the numbers of employees who are parts planners and any other resources supporting slow moving parts for older vehicles would be among the first things a short sighted management team would want to cut.
 

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On the other hand, I have seen that for BMW's at least you can sometimes buy OEM parts that are exactly the same as Original BMW parts for a much lower price also. For instance, I once bought some TRW branded M3 control arms where the "M3" logo was just ground off the metal so they could sell it that way at lower cost ....
 

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On the other hand, I have seen that for BMW's at least you can sometimes buy OEM parts that are exactly the same as Original BMW parts for a much lower price also. For instance, I once bought some TRW branded M3 control arms where the "M3" logo was just ground off the metal so they could sell it that way at lower cost ....
That happens occasionally with Mercedes parts too. I bought some Lemfoerder control arms for my 240D where it was apparent the star was ground off.
 

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On the other hand, I have seen that for BMW's at least you can sometimes buy OEM parts that are exactly the same as Original BMW parts for a much lower price also. For instance, I once bought some TRW branded M3 control arms where the "M3" logo was just ground off the metal so they could sell it that way at lower cost ....
This is exactly what I was referring to when I said that marketshare is lost when a Genuine supplier sells parts "out the back door". While you can sometimes source a part this way, its a rare instance and you can't count on experiencing this all the time. The loss of marketshare for the manufacturer as a result of this causes them to have to raise their prices or cut their costs.
 
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