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S600 misfires, new coil pack and plugs

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S600 misfires, new coil pack and plugs

Old 06-15-2018, 01:27 AM
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S600 misfires, new coil pack and plugs

I have a 2007 S600. I had been having sporadic misfire/knock about every other month for about a year when at very low RPM (such as when going slow at a drive-thru). When this happened I would get a flashing CEL and would turn off the engine and back on and I would be fine for about another month or so. I had the transmission re-built in Nov 2017, and I thought the misfires were related to failing TCC (torque converter clutch) not dis-engaging and putting the engine in a bad state and mis-fire on both side. I had the TCC solenoid replaced about 2 month after the transmission was rebuilt (TCC was hard engaging), and I hadn't had much issues with misfires since. I did have a semi-continuous CEL that was due to fuel vapor vacuum line and didn't think much of it.

Finally, while driving on the highway last week about 30miles from home, my dash light dimmed and it seemed that my transmission was not shifting properly (CEL had already been on due to fuel vapor vacuum line). Acceleration was weak, but I was able to continue cruising at 80 on the highway, had no drop in MPG (from what I read on v12cipack.com it seem that cylinders 7-12, left bank, are shut of during cruise, which would explain no drop in MPG if true). I figured if the car is drive-able, and my CEL wasn't flashing I would try to make it home. I made it home fine and pulled the codes; reading P300, P307-P312.

After reading this thread, I was inspired to start taking things apart instead of taking to an INDY, figuring I would save >$1000 on labor alone, and I could source parts cheaper than they would sell them to me. So I started unbolting and removing things. After reading on v12icpack I thought I had a bad voltage converter and decided to open it up to see if there was anything obviously wrong/burnt, but it actually looked good inside. I was able to price a genuine rebuilt part from about 3 MB resellers online for between $360-$420 (some dealers and resellers were as high as $850). Before ordering a voltage transformer, of which I read for a full bank misfire it is 50/50 between transformer and coil pack. There is even a place in Boca Raton, FL just an hour from me that does testing and rebuild of this unit (testing $120, and if it is bad they put that full amount towards the $300 rebuild service; see programainc.com for details). I figured I'm better of getting a new unit for $360 than risking a $120 test and then $300 rebuild. While trying to decide what I was going to do I decided I wanted to open the coil pack and see if perhaps I had a better choice to make (ie if the the coil pack was obviously burnt inside I would just replace that).

I removed the left coil pack (driver side). As an aside, my engine bay has been a dirty mess since I bought the car in 2016 from a guy in PA, but I was never able to find a detailer willing to wash the engine bay (they apparently gave up their advertised services due to liability when power washing electronics under the hood) and had thought it futile to do it myself, until I watch a video online of someone doing magic to a nasty engine bay with a rag and soap. So I started cleaning up and began with the outside of the coil pack. The first thing I noticed was a bit of rubbery gunk on the crevices of the plastic cover for the coil pack and tried to scrape it off. Initially I thought it was some dripped silicone that had gotten caught in the corners, but as I started scraping it off from the full length of the coil pack I started seeing cracks. When I finished removing it all, I pried the cracks open only to find that it was the repair job for someone who had tinkered with the coil pack internals. I saw a bunch of 'R's written on some components (suppose this meant repaired), and I also noticed that some of the metal tubes that hold the coils where different than the others. Immediately, I thought this must be the defective component and not the voltage transformer. Actually, the part number for this coil pack is 2751500580, which has been supplanted by new part number 2751500780. I searched high and low and found one site selling 2751500580 for only $860 new (one of those common MB parts catalog webpages, like a site that is a template for MB dealers to use), though that same site sell 2751500780 for $1050. Miraculously, though, I found my local Coral Gables dealer selling the newer part number 2751500780 for $960+tax, which is the lowest I have found a retail place selling it for. They wouldn't even honor the online price if I went direct through their parts department, so I had to wait until Monday when the 'internet' guy was in to process the order, even though I would still pick it up in the standard parts department. (Seems that Cutler Bay Mercedes, which is owned by the same owner as CG Mercedes, does a price match). I also tried calling Mercedes of Miami, but they wanted to shaft me with the full retail of $1440, no even the standard 10%-20% they have given me in the past.

While my car was sitting idle I also decided to replace the oil pan gasket which had started leaking suspiciously after getting my transmission re-built and also asking that shop to install engine mounts while they had the car up there anyways. I THINK they probably jacked up the engine by the oil pan in oder to replace the mounts, and this must have squeezed the gasket out in places. And from looking at my oil pan it also seems there are stress cracks in the place that it would have been jacked up.

Long story short, I just replaced the spark plugs this evening and I'm going to do the coils this Saturday. The reason I came here is because after removing my plugs and putting a boroscope in the plug-holes I saw some fairly horrifying stuff. Seems the pistons are completely coated with carbon, and most of my spark plug holes appear to have oil on them as if someone has greased them up. Some of the plugs have crud on the threads, so I dont know if this is burnt oil that dripped from a leaky valve cover (only seems there is one spot that has a minimal oil leak that is of no concern), or is this oil that is coming from inside the piston chamber. Or could this be burnt anti-seize?

Does this look really bad??? What causes this? Can I pour a bottle of Seafoam into each cylinder and hope for the best?

My car burns about 2-3 quarts of oil over 5,000 miles, which I've been told is not terrible, but not good either. Apparently, for a manufacturer to replace an engine under warranty it would have to burn about 1 quart in 600miles, so I'm about double that. I also drive this car extremely hard.


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Old 06-15-2018, 09:03 AM
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Nice write up on your progress.
Do all of the sparkplugs look like that? It would seem that the oil is dripping down from above into the sparkplug holes.
From the looks of the sparkplug it looks like it would be fouled out and not sparking correctly, which contributes to your misfire.
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Old 06-15-2018, 09:37 AM
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Thanks for the write up, always good to get more parts sources and info. Curious as to why you didn't do the voltage control rental from V12icpack?

http://www.v12icpack.com/#!/Rental-F...egory=15310219
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Old 06-15-2018, 11:36 AM
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I'm not an engine expert, but your cylinder wall looks pretty scarred. Maybe oil is seeping past the pistons too much. Hopefully a mechanic will see your pictures and let you know for sure. Good write up so far!
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Old 06-15-2018, 11:53 AM
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Borescope some of the other pistons, if they all look like that, there's a serious mechanical issue.
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Old 06-15-2018, 12:34 PM
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Thanks for the response guys, glad to see other passionate MB owners on here
---ItalianJoe1: Borescope some of the other pistons, if they all look like that, there's a serious mechanical issue.
Yes, I did borescope all piston on that side and they all seem to have black carbon buildup on them and similar scarring on the side wall, but only on the front & aft side of the cylinder. Though this one was the worst one with what looks like waves on it. I am fearful of serious mechanical issues, but when all of them look the same, I'm hoping that is just an indication of something somewhat innocuous, such a oil seeping past the piston rings slowly over time. From a debugging perspective, I would be more worried if I found this in only one cylinder as that would mean for sure there was something not right with the particular cylinder as opposed to perhaps overall seepage, but I'm going to ask around. The other ones had a more uniform crusting on them. About half the plug holes had what appears to be oil on them, but I only saw oil in one corner of the valve cover gasket and it didn't seem to be a significant amount. In fact, when I pulled out the coil pack there was some oil on it that only ran about half way down, and it appeared to be light colored/unused oil.
I do plan to take off the right-side coil pack (btw, P/N 2751500680; or prior/superceeded part number 2751500480) and inspect those cylinders to compare. I'll probably crap myself if they all appear clean as a whistle as that would mean this is a very long project ahead to redo the problem side o_0.

---lionsfan54: Thanks for the write up, always good to get more parts sources and info. Curious as to why you didn't do the voltage control rental from V12icpack?
Actually, I did consider this and I read extensively through that site, which is what kind of inspired me to tear things apart. So I opened the VC to see if any capacitors had bubbling or popped tops, but I did not see any of that. [Coincidentally, It also appears that Clark is on vacation and had his trailer blow up and catch fire as he put a paragraph on it at the top of his page, so not sure how delayed orders are]. Additionally, since I removed the coil pack and saw that it was the original P/N (ending in 580), and that it was opened and repaired already, and also seeing that the other side has the new P/N (ending in -680 instead of -480), I figured the best spent effort for time and money is to replace the already repaired original part. In the end, if I have to end up replacing both, its worth having a new coil pack in there so that I don't have to touch it again for hopefully 60k+ miles.


After googling around, I saw some people are cleaning the carbon with pine-sole. I'm wondering how radical it would be to pour something in the cylinder and let it soak (hopefully not past the piston rings), then vacuum it out.
I'm also wondering if walnut shell blasting can be done through the plug hole, or if the valve cover has to come off?
It also says on the can of seafoam that it can be added directly to the oil!? Anyone had any exprience, I used to be afraid of harming the delicate balance that is a V12 M275, but after tearing apart the car and putting it back together I'm getting more confident and realizing it just another engine, but with more parts
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Old 06-17-2018, 11:46 PM
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Ok, I finally took off the right side to compare what the cylinders look like. Seems these have significantly less carbon on them. Someone at work told me that the more carbon you have that means that your engine is running to rich in fuel/air mixture, which is likely cause by the misfires and the conditions leading up to it. I also saw a video on what an engine with a head gasket failure looks like and the cylinders in it look REALLY clean (
). Turns out that when you have a bad gasket and coolant leaks into the combustion chamber, it will 'steam clean' your engine and result in essentially zero carbon build up. Which apparently is how this service works, http://www.carbontekusa.com/, I'm thinking of getting this done after I put everything back together and resolve the CEL misfires. Before my car had this serious problem with the engine shaking due to 7-12 misfire, I also noted a noise coming from my cat, so seems perhaps all the unburnt fuel may also have lead to damaging the catalytic converter, though I don't seem to have any codes specific to that. I have read where others head a sound of gravel coming from the primary cats, that they cut them out completely because it means there is broken material rolling around in there. Something to consider especially if I'm going to have all that carbon making its way out, I dont want to clog it up.

A second question I have, and I hope I'm not screwing it all up by doing this. When I removed the plugs from the right side, the non-misfiring side, I decided to try and clean them up a big. They did not have anywhere near as much carbon buildup as the left side, but wanted to get them as clean as possible. I heard that taking a blow torch to them will burn of any carbon/other contaminants, however I'm not sure if these plugs are special and it seems I' may have cooked one. After hitting it with the torch for a good 2-3 min, seems there is more custy ash (white) on there than black carbon there was before. Not sure if these OEM plugs are coated in some special material, but seems the torch is eating away at the white part surrounding the electrode. So instead, I decided to dip all the ends into a cup of seafoam and let it soak overnight.

Is this a good idea??
Will seafoam penetrate into the plug internals and ruin them? Or worse, cause a short and lead to having to replace the RH coil pack as well??

Here are the pics for the RH (passenger side) Cylinders:




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Old 06-18-2018, 12:19 AM
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Quick followup, after putting in the new coil pack, I noticed a bunch of hoses running to a box sitting ontop of the left side valve cover. Seems there is a nipple on it with no hose connected. Is something supposed to go on here?

Something supposed to be plugged in here???


What is this and is a hose missing from it (see other pic)
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Old 06-18-2018, 03:47 AM
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Originally Posted by wampa007 View Post
Quick followup, after putting in the new coil pack, I noticed a bunch of hoses running to a box sitting ontop of the left side valve cover. Seems there is a nipple on it with no hose connected. Is something supposed to go on here?

Something supposed to be plugged in here???


What is this and is a hose missing from it (see other pic)
yes normal

be careful when you put the intercooler back passenger side
if you don't do it carefully you might break of a hose on these shutoff valves
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Old 06-18-2018, 02:48 PM
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Update on my interaction with NGK tech support on the proper plugs here: https://mbworld.org/forums/m275-v12-...ml#post7481892
Long story short, stick with the OEM part # NGK IFR6Q-G. This applies to NGK products, I can't speak for other brands.
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Old 06-18-2018, 08:14 PM
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Don't torch your plugs or try to clean them, just replace them. Yes it's not the cheapest way to go, but if you wanted the cheapest way, a twin turbo V12 Mercedes is probably the wrong car for you.

Only use the specified NGK plug (OEM is that NGK). No substitutions. The Ion current sensing function of the coil pack is calibrated with a specific plug and a different plug won't work the same.
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Old 06-19-2018, 03:00 AM
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Bosch 0242236571 FR7KI332S is OEM to me too
maybe europeen orders have Bosch and US Japan with NGK's
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