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'89 S124 200D / '95 C124 E320 dogleg / '95 rod bender
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73 Posts
Discussion Starter #1
Hello everybody,
I need your opinion about the cap in the picture below. This S600 starts to misfire when warm and has no power at all and last time when this happened to me it was a worn out cap/rotor on a M104...
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,727 Posts
Pretty ugly. It looks like the carbon brush in the center of the cap is badly worn. Tons of corrosion on the terminals.

When you change them, pull the rotor drive under the rotor, and clean and inspect the base under it for cracks and/or carbon tracks.

Jon
 

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1992 500SL, 1993 300SE, 1997 S320L, 2000 C230K, 2003 E500, 2005 Smart ForFour, 2008 Smart ForTwo
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318 Posts
Pretty ugly. It looks like the carbon brush in the center of the cap is badly worn. Tons of corrosion on the terminals.

When you change them, pull the rotor drive under the rotor, and clean and inspect the base under it for cracks and/or carbon tracks.

Jon
So you’re saying to replace the rotor bracket?


Sent from my iPhone using Tapatalk
 

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'89 S124 200D / '95 C124 E320 dogleg / '95 rod bender
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73 Posts
Discussion Starter #5
Where do you get this parts from? Dealership quoted above £600...
I was looking for a good quality replacement - if such things exist!
 

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1994 s600 coupe
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380 Posts
I just went through all that, sorting out the different types of rotors and caps. now they make at least 4 different types, some with shorter rotor tips than original. the wrong combination will give you a bigger gap between rotor tip and cap contact, if you go the thread you can see.
 

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1994 s600 coupe
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380 Posts
in case you didn't see it, here's the thread showing the various cap/rotors available.
if you can find them, you want the oem MB Bosch cap/rotor, the late-93 to 95 replacements.
you can run any, any will work, even the 6-cyl cap/rotor from the 300SL,
but the late model W140 set is the best.

 

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1994 s600 coupe
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380 Posts
yes that's what I thought JAL meant by insulating plate, that shallow bowl-like part behind the rotor. that one looks good to me. but maybe remove rotor and rotor bracket mount, and take it out and get a better look at both sides.

you can salvage that cap/rotor for the time being, but taking a fiber brush on a dremel, and gently cleaning the contacts on cap and rotor, don't take a lot of material off, just enough to get the burnt corrosion off.
it'll run better but with slightly larger rotor to cap gap. when I cleaned both sides of mine, the ignition voltage went up,
but the car ran better, until I found new replacements.
if you want to low buck it, you can get cap/rotor sets for $110 per side, from Rock Auto. that's the best price I could find.

don't throw the old cap/rotors away, keep them as spares. the caps are over $100 each new, and the rotors are now $80 each, for the original Bosch parts. if you clean those caps, and use the early extended tip rotor from the 1991-93 model, with a center bushing, you can reuse them. the longer tip restores the rotor to cap contact gap.

some of the replacement aftermarket caps/rotors have really big gaps, like the Bremi, uses a shorter rotor tip, you'll see .090" gap on some. which is like 3x what it should be. that makes the coil and ignition modules work like hell all the time, to bridge the gap.
the biggest gap in the system should be at the spark plugs, not in the cap or anywhere else.

you've got the original rotors in there, I can tell by the little mercedes benz star emblem on the rotors in pictures. you can clean those rotors and reuse them, I reused one of mine. one ended up losing .003" after cleaning, the other lost nothing, so I reused it.
the cap contacts generally get eaten away by the spark and must be replaced. those rotors are $80 each, don't throw them in the trash. you can throw them in my trash bin...;)
 

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'89 S124 200D / '95 C124 E320 dogleg / '95 rod bender
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73 Posts
Discussion Starter #11
Thanks everybody.
Started fine after I put the cap back, went away for 5 minutes and then... not start anymore. I have spark on both sides and I have petrol... :(
 

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'89 S124 200D / '95 C124 E320 dogleg / '95 rod bender
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Discussion Starter #12
1994v12: I might end up giving away the entire car not only the cap/rotors.
 

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1994 s600 coupe
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380 Posts
I left the main coil wire off one side of my V12 on two occasions, what it does it shut down the entire engine, and it will just crank, and not start. check the main coil secondary wires, make sure they are fully seated into the coils and caps. also, spray some PB Blaster or WD40 on the small primary connections on each coil, then loosen, and retighten them. you may have a corroded connection there. the coils are located up front facing forward in an area receiving road spray, salt, moisture when driving down the road in winter or rain, or hitting puddles of water. mine were slightly corroded. another thing, there are ground wires on a stud on each side, next to coils, spray-loosen-tighten each of those both sides. there are also (2) ground lugs near EZL modules on top of each fenderwell, 2 on each side, total of 4 more ground lugs with wires attached, do the same to them.
also pull all your fuses out of the fusebox, check for corrosion, file fuses to remove any corrosion, spray fusebox connectors with electrical cleaner, plug all fuses back in. also check the 4 fuses in the end small module in coffin box, in the ECM area.

these cars can be frustrating, they are overly complex in many ways, and more than once I asked myself wth did I buy this thing. but hang in there. if you keep chopping away at it, you'll eventually find it. but word of advice, just like a doctor, diagnose, but do not do any harm. I've spent months just finding and repairing what previous hacks did to my car. so keep it bone stock don't try anything out of the ordinary.

valicaddy, where are you located ?
 

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1994 s600 coupe
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1994v12: I might end up giving away the entire car not only the cap/rotors.
hey valicaddy, another guy with half a V12 engine stone cold,
just found out it was a coil causing the problem.
check your coils, and connections, secondary wires off coil to dist. caps.
 

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'89 S124 200D / '95 C124 E320 dogleg / '95 rod bender
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Discussion Starter #15
I am located in UK.
I never modify things on a car if parts are available...
Due to weird working hours I have to wait for my days off to start checking all things suggested.
Until then...
We have some more good news!
 

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1994 s600 coupe
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don't go ripping into your harnesses over those little cracks in insulation, unless there's long sections of it bare, rubbing against other long sections bare, it means NOTHING electrically. for a bare wire to short out, it has to touch a metal ground, or another bare wire. those are just tiny cracks. look at the ends of the harness where it attaches to the MAF sensors and the throttle bodies, repair it THERE if it's bare and touching wire to wire. don't disturb that harness you just posted pics of.

AC power from our household suppliers travels thousands of miles on telephone poles, with no insulation at all, just a bare wire. and it's many thousands of volts. it has to touch ground or another wire to create a problem.

there is also this product called LIQUID TAPE that will cover bare sections of wire, you paint it on with a small brush, it looks like thread sealer or gasket sealer, but dries into a solid coating like thick paint. I repaired my harness ends with it, and it works. we are talking very low voltages on a car, 12 volts, often less than 1 amp, and often less than 6 volts.

I would not want a bare wire on a main power feed to the starter or alternator or a major current drawing accessory like rear window defogger, or AC compressor clutch. but for those small sensors, computer feeds, those little cracks will live for now. just so they aren't touching each other bare. if you'll notice ground straps from engine to frame, etc. are bare braided wire.
 

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'89 S124 200D / '95 C124 E320 dogleg / '95 rod bender
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Discussion Starter #17
Left side ground behind headlamp was clean - I think I’ve seen enough dirty/corroded ones...
Put the wires back and - don’t think it’s related to what I did but the bi+ch started...
Underpowered, pulls like a straight 4 diesel and at one point ASR light came on. Lovely.
 

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1994 s600 coupe
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how bout that...clean all the grounds, start with the easy cheap stuff first.
clean them on both sides by coils, and both sides by the ezl ignition modules.
all told there's at least 6 studs with grounds on them.
there's also a grounds on the inner fenderwell under/behind the drivers/left side air cleaner,
you have to remove air cleaner to get at it.
unplug the maf, intake air, throttle bodies, spray all the plugs with electrical cleaner.
pull all the plugs out of the ezl ignition modules both sides, and spray the sockets and plugs.
basically anywhere you see plugs, connections, grounds for engine, clean them.
also remove all the fuses, visually check every one, and sand the flat pins, and plug them back in.
over half of the pins in fusebox on my car, had heavy white corrosion.
when I was done everything started working again inside the car,
and I found 3 blown fuses, including one in the end ecm module in the coffin box
that shut the ASR light off in my car, that's all it was.
these cars are old, we're talking about cars that are mechanically very stout,
but electrically need to be completely reharnessed due to corrosion at some point,
or at least all the connections cleaned.
it's like the space shuttle, the body is solid, the electrics goes bad.
 
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