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Discussion Starter #1
Hi folks,

The S600 TT is a very smooth engine...until I drive it "enthusiastically" a bit and things get warm under the hood. Then, one of the cylinders starts misfiring, and I get a CEL. STAR Diagnostics says it's Cylinder #12. So, I went through all the injectors with the DAS tester, deactivating each one and turning it back on with the engine running. All 12 fuel injectors seem to be working fine.

When the engine cools down, that #12 cylinder starts firing again. As long as I don't drive too "enthusiastically" and thus keep the under-hood temperature somewhat down, that cylinder doesn't start misfiring; engine purrs smoothly like a V-12 should.

My old electronics-tech instincts tell me, "hmm...transistors in the ignition coil pack...lots of heat...recipe for eventual failure."

I will certainly replace the spark plugs, using iridium types, hoping that will solve the problem. But I kinda doubt it in this case because of the apparent temperature effect, so I kinda suspect it'll be the ignition coils.

Should that prove to be the case....

Does anyone have experience with these "rebuilt" or "remanufactured" V-12 ignition coil packs from the likes of V12ICPack, Direct Wholesale FL (the eBay seller), and such? What is your experience on a rebuilt coil pack vs. a brand new one? I have looked in the Encyclopedia (didn't see anything), and on MBWorld (mixed reviews).

Thanks!
 

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The # 12 plugs are the most difficult ones to connect when you remove/install the coil pack.
I had a misfire there, and on removal found that the coil was crossfiring to the shield tube right thru the rubber insulator.
MB WIS says replacement of these red silicone rubber insulators is mandatory on coil pack RR.

Fixed the misfire on mine, and never came back.

Check this before you spend big $.
 

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Discussion Starter #3

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Discussion Starter #5
OK, thanks for that tip. I'll give the dealer a call.
 

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before you go thru all this, here's some pointers:
1) Once you remove the coil pack, remove all the rubber insulators (whatever they call them)
2) very carefully inspect them for any irregularities (such as burn marks)
3)wash them in dish wash detergent
4) rinse and let them dry thoroughly
5) discard any suspects
6) inspect and clean out the coil tubes and contactor springs
7) reinsert the declared "good" rubber inserts
8) apply a very small dab of silicone di-electric to the "mouth" of the inserts to make them go easier onto the plug insulators
re-install the coil pack.

This is what I did on my car, and I did not replace all inserts, only some that looked iffy.

Never got a misfire code after that.

BTW: A misfire code cyl#XX does not mean the cylinder misfired, it means one of the two plugs did. Does not tell you which one of the two.
Good luck!
 

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Discussion Starter #7
I'll try that first. Thanks! There are 24 new rubber insulators on the way, just in case. Assuming several or even most of the rubber insulators look "good", I'll hae extras for the other cars. The S500 project car also misfired once on cylinder #5. Already ordered a coil pack for it, which has arrived, so I'll be inspecting its rubber insulator as well.

Question: if only one of the two plugs does misfire, that means the other one should still have gone off and lit up the air-fuel mixture. I would think that, while the combustion might be a little less efficient, there would still be combustion and thus no "lumpy" (for lack of better word) feeling from the engine, is that correct? Sort of like the old saying, "an heir and a spare".
 

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I had the good folks at V12icpack, Mercedes S600 ignition coil pack repair, ECU, misfires V12 engines - Home rebuild my passenger side coil after a misfire condition. I knew it needed rebuilding because the coil tube itself was loose (soldered components shouldn't be loose...). Discovered when I was changing the plugs.

The service was prompt, the price was reasonable and the coil has worked great since the repair six months ago.

They'll even loan you a coil pack if you want to trouble shoot.

I would use them again in a heartbeat.
 

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Discussion Starter #9
Took the coil pack out for cylinders 7-12. Noticed there's oil coming out from around the valve cover gasket...and there was a bit of motor oil on the rubber insulator boots for cylinder 12! That's the misfiring cylinder and the only one that had oil on the rubber boots..

I think I found the problem. :) But now I've got a question (bottom of this post).

Valve cover gaskets for both left and right banks are on the way. I went ahead and ordered Genuine Mercedes because it was only $5 more. Total for both was something like $65, shipped. The OE one was the same price, and the aftermarket "made in China" one was only $5 less. For that, I'm goin' Genuine.

Also, it appears that these coil packs might be the "new and improved" design, per this MBWorld thread.

V12TT Coil Pack DIY Replacement - With Pictures - MBWorld.org Forums

Mine do have the voltage warning sticker and the "780" numbers in the part #. Matter of fact, the part # of this one is A2751500780. It appears to be made by "Temic".

Is there a way to determine when it was made? This is a 2003 vehicle, so if it was replaced, it'd be kinda nice to know when.
 

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Discussion Starter #10
Well, I figured, might as well replace the valve cover gaskets since I'm in there anyway, and both of them are leaking. So, I took the valve cover off for Cylinder Bank 7-12 (right side if you're looking from the car's front, left side if you're behind the wheel), cleaned it thoroughly, put a new gasket on there with a very thin coat of RTV, and letting it cure for a few days before I fire up the engine. Also replaced the spark plugs and the insulator boots.

Good thing, too, because I believe I've found out why Cylinder #12 was misfiring!

Here's the picture of the spark plugs for Cylinder #11, which was firing just fine. For the new folks like I was (and still am), all W220 engines have two spark plugs per cylinder. Thumbnails are clickable.




And here are the ones for Cylinder #12!



Quite a contrast, huh? :) Ain't all that gunk on the tips just lovely? That plug on the right should run for Congress, with all the gummed-up works....

As they say in the South, Ah thank Ah know what the problem is now. :-D

Sooooo....the moral of the story here, since I'm a moral young man (yeah, right), is that it's a good idea to actually replace your valve cover gaskets every so often. ;-) After 160,000 miles and about 13.5 years, the one for cylinder bank 7-12 had lost virtually all of its pliability and is pretty much hard plastic at this point. My guess is the same is true for cylinder bank 1-6 as well, so I'll be replacing that one, too, along with plugs and insulator boots. And yes, the spark plug wells for Cylinder #12 had plenty of oil in them, as evidenced by the bottom of the two ignition coils for that cylinder, and the spark plug socket (covered in oil) when I removed the plugs.

Now, all that's needed is to make sure I put things back together right. These engines are not exactly Honda Civics, are they? :-D
 

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Well, I figured, might as well replace the valve cover gaskets since I'm in there anyway, and both of them are leaking. So, I took the valve cover off for Cylinder Bank 7-12 (right side if you're looking from the car's front, left side if you're behind the wheel), cleaned it thoroughly, put a new gasket on there with a very thin coat of RTV, and letting it cure for a few days before I fire up the engine. Also replaced the spark plugs and the insulator boots.

Good thing, too, because I believe I've found out why Cylinder #12 was misfiring!

Here's the picture of the spark plugs for Cylinder #11, which was firing just fine. For the new folks like I was (and still am), all W220 engines have two spark plugs per cylinder. Thumbnails are clickable.




And here are the ones for Cylinder #12!



Quite a contrast, huh? :) Ain't all that gunk on the tips just lovely? That plug on the right should run for Congress, with all the gummed-up works....

As they say in the South, Ah thank Ah know what the problem is now. :-D

Sooooo....the moral of the story here, since I'm a moral young man (yeah, right), is that it's a good idea to actually replace your valve cover gaskets every so often. ;-) After 160,000 miles and about 13.5 years, the one for cylinder bank 7-12 had lost virtually all of its pliability and is pretty much hard plastic at this point. My guess is the same is true for cylinder bank 1-6 as well, so I'll be replacing that one, too, along with plugs and insulator boots. And yes, the spark plug wells for Cylinder #12 had plenty of oil in them, as evidenced by the bottom of the two ignition coils for that cylinder, and the spark plug socket (covered in oil) when I removed the plugs.

Now, all that's needed is to make sure I put things back together right. These engines are not exactly Honda Civics, are they? :-D
Was your misfire issue resolved after this work?
 

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Discussion Starter #12
Not yet. Been waiting on another part, a coolant hose, apparently on the Slow Boat from Deutschland. I said screw it and just used good-quality (made in USA) general hose, and that should work until the Genuine-MB one eventually arrives. Now I can actually safely start the car, so we'll find out this weekend.
 

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Discussion Starter #13
Got a hose on there, intercooler secondary coolant circuit filled up. Was working fine for a bit...then the misfires came back. Cylinder bank 1-6, as before, with occasional misfires of a couple of cylinders on the other bank as well.

I have discovered another pattern. After this happens, I'll clear out the codes with SDS. Then I'll start the car and IMMEDIATELY start driving, i. e. I'm within motion in about 5-7 seconds. If I do that, then the misfires do not re-occur unless the car subsequently sits at idle for a few minutes. At stop lights, which generally last a minute or so, I'll feel just a little bit of roughness in the idle, but cylinder shut-off does not occur. To help with preventing cylinder shut-off, I'll keep the idle at just above 1,000 RPM at the stop light; this is if I think I'll be sitting there for a few minutes.

New catalytic converter assemblies, both left and right, are on the way from MBOemParts.com. These cats are 175,100 miles old and are probably due.
 

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Got a hose on there, intercooler secondary coolant circuit filled up. Was working fine for a bit...then the misfires came back. Cylinder bank 1-6, as before, with occasional misfires of a couple of cylinders on the other bank as well.

I have discovered another pattern. After this happens, I'll clear out the codes with SDS. Then I'll start the car and IMMEDIATELY start driving, i. e. I'm within motion in about 5-7 seconds. If I do that, then the misfires do not re-occur unless the car subsequently sits at idle for a few minutes. At stop lights, which generally last a minute or so, I'll feel just a little bit of roughness in the idle, but cylinder shut-off does not occur. To help with preventing cylinder shut-off, I'll keep the idle at just above 1,000 RPM at the stop light; this is if I think I'll be sitting there for a few minutes.

New catalytic converter assemblies, both left and right, are on the way from MBOemParts.com. These cats are 175,100 miles old and are probably due.
Are you quite sure this is not an ignition related issue before installing new cats?

Have you test fitted known good coil packs and voltage transformer for example? If you are located in USA you could send your items to v12icpack.com for testing or even hire a rebuilt set from him for testing in car. It doesn't matter how "nice" the coil packs may look they could well be faulty.
 

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If you think the cats are causing the misfire condition could this theory be tested first by removing the cats and running the engine?
 

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Use a threaded sleeve extension to lift the Lambdas outta the exhaust flow ;)

It could be likely, don't know for sure, simply removing CAT's will cause the car to throw misfire codes anyway, as it will shut cylinders down to protect CAT's ;)
 

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Use a threaded sleeve extension to lift the Lambdas outta the exhaust flow ;)

It could be likely, don't know for sure, simply removing CAT's will cause the car to throw misfire codes anyway, as it will shut cylinders down to protect CAT's ;)
search google for o2 sensor spacers to compensate for partially non efficient cats.
If that doesn't work, look for spacers with their own "mini cats" as integral part to correct the readings, and "fire up" the cats to clean them. Worked on mine.
 

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Discussion Starter #19
Are you quite sure this is not an ignition related issue before installing new cats?

Have you test fitted known good coil packs and voltage transformer for example? If you are located in USA you could send your items to v12icpack.com for testing or even hire a rebuilt set from him for testing in car. It doesn't matter how "nice" the coil packs may look they could well be faulty.
Indeed, I actually have replaced not just the voltage transformer, but both ignition coil packs with Clark's rebuilt ones a couple of months ago, as I had thought that was the issue. Same problem. I had already replaced the spark plugs--all 24 of 'em--two years ago with the OEM NGK Iridium plugs, so we know those are good, too. Did all four O2 (Lambda) sensors.

Here's an interesting thing that happened last night. We went out to dinner last night, and we were at idle at a stop light for about 30 seconds, it happened again. I lost nine (yep, 9) cylinders; the entire 1-6 bank and three on the 7-12 bank. The engine was running as roughly as you might expect. Just to go easier on the engine, I shut it off until the light turned green, and...LO AND BEHOLD! I had all 12 cylinders back. The house wasn't far away, so we limped back home (we were still rather close) and switched to her car, the project 2000 S500, to go have dinner. SDS showed the misfire codes, but "STORED" instead of "CURRENT and STORED", since it had cleared up after shutdown and restart. Kinda like Microsoft Windows that way. :)

Again, this only happens at idle. If I, say, switch to neutral and keep the RPM's up at anything from 1000 and up at the stop light, I don't lose cylinders. That's how I've been driving it this week, thus far, and as long as I do that, the engine stays smooth and apparently retains its full power.

To @Dave2302 's and @Kraut56 's point about testing whether the cats are bad...remember, they're 175,100 miles old now and are probably the originals. It's only about US $450 and change per side for the entire assembly anyway from M-B, after the core charge refund (you send your old assemblies back to M-B for rebuilding), so I don't mind doing it. This will definitively tell us, though, whether or not it's a cat problem, 'cause I'll have brand new factory ones in there. Will report back as soon as I can.

I really wish we had some good, steep grades for Italian Tune-Ups. Colorado has them. This area is not so blessed....
 

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Hi,

I here ya, but I've seen MB Cats (and DPF's on Weasels) that are still fine at 300,000 miles ;)
 
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