Here's a bit of a story and a small question at the end:

I'm on the 4th week of a 6-week half-vacation in Greece. Made the trip through Italy + ferry and all went well, until 3 days ago when the CEL lit up and then started flashing before settling on on again, while the car shaked like crazy both when idle and when accelerating. I have Carly, and it told me that there were two codes, P030585 and P030022, indicating that, well, cylinder 5 had a misfire.

Spoke to an authorised repair centre (but not a dealership) and I was advised to empty the tank (filled with 95 RON fuel from a reputable gas station that I know personally) and fill it up with 100 RON. Sure, did that and also added some injection cleaner which I believe is more placebo than anything, but what the heck. I was curious though, if it were the fuel, why would it only misfire at C5 instead of doing it at random?

The issue went away for a day, then it came back. Was again advised to "let the new fuel seep through fully" (sigh) and predictably, it went away and came back again, a bit sooner this time.

I realised that I would have to actively engage a mechanic and also make sure I could take advantage of my warranty in case this got expensive. Problem is, MERBAG (Mercedes Switzerland) and Mercedes Hellas (Greece) won't do this for you, you must instead pay the repair costs upfront then get reimbursed when you get back. Not a problem, unless we're talking a few thousands of Euros, which would have a significant currency conversion fee. Spoke with the local dealership (where I happen to know the owner) in order to squeeze me through their schedule and as I explained the situation to the chief mechanic and how I was a bit pressured for time, he told me that "hey, this may get expensive and take time. There is a good possibility you won't be able to have the car ready in time (13 days)". I generally avoid dealerships, unless I have a warranty.

I visited the first repair centre again and asked the guy if it's easy to swap the spark plugs, the coils and the injectors between cylinders in order to find out what might be causing this. Plugs & Coils were relatively easy, Injectors were out of the question since it would require more elaborate disassembly of the engine. The shop is small, so I was present while he was working. I saw him working on the left bank, removing the coils and then the spark plugs. He told me that the coil on the 5th cylinder had a bit of rust, but (apparently) this was no reason to worry. He also said that the spark plug was a bit dark, indicating inefficient ignition, hinting at the coil.

After replacing it, I barely drove 1Km and the issue came back, as expected. Drove back again, he hooked it up to Xentry and lo and behold, Cylinder No. 5 still misfired. At this point I was hoping I could avoid the dealership, but that ship seemed to have sailed and I was going to have to wait until Monday. He explained to me that if it's not the Injector at fault, it was going to require more elaborate investigation which could probably be costly, in both money and (crucially) time.

I tend to not leave well enough alone though so I started looking online for a cylinder diagram for the M176 engine. I eventually found one and what do you know, according to that, the 5th cylinder was on the right side. So, after a phone call and an explanation, whilst telling the (otherwise friendly) guy that I'm not trying to tell him how to do his job, I drove back, showed him the diagram and he offered to open up the engine again and try to do a swap of the coil & the plugs from the other side, for free.

After that was done, I turned on the engine and it started immediately shaking, so I didn't even have to leave the shop in order to get the CEL to light up. And there it was, Cylinder No. 7 now was playing hardball and refused to work properly. Since we put the coil pack and the plug into different cylinders we knew it was the coil that was the cause of the issue. At this point I tipped him a 20 (in case I need priority support in the near future or next year) he told me he will order a new coil tomorrow because it was a bit late, and hopefully I will have the car running properly next week.

I asked him to tell me why he didn't know the correct bank to work on, he responded that this is what the online manual said. To be honest, I am not sure I believe him, but that's besides the point. If I hadn't had the curiosity to look this up myself, I would probably have wasted time in the dealership and seriously risk losing my already paid-for ferry & hotel tickets, also having to extend my stay (not a problem) and explain it to my job (could potentially be a bit of a problem). I am unwilling to easily trust another mechanic now, unless we're talking about the dealership in Switzerland, simply because I still have the warranty. How the hell can I tell a bad one from a good one after that expires and assuming I still keep my car?


Thanks for reading so far. And my question: Based on your experience, is there anything else I ought to look at before calling it done? Cracks? Related components, etc?

 

How many miles on your car? Do you have the V8 M278 engine?

I am asking miles, because the dreaded bore scoring often shows up on cylinder 5. Have to test compression for that though.
Hopefully its not that, and just plugs, coils or injectors.

Is cylinder 5 the one on the left (driver side), front?

Fuel additives actually do work. Depending on the additive of course. Gasoline makers put in the minimum amount of additives thats needed by law. Sometimes you need some extra additives for cleaning.

 

OP stated he had the m176 V8.

 

Hi, as @95Sinned420 stated, I have the M176 (S560). The cylinder when standing in front of the car's hood, is on the front right. I haven't seen any other codes, but as soon as we moved the coil pack to another cylinder, the error message changed to indicate the new cylinder, so I'm guessing it's only the coil pack. I'll have it delivered and installed by Monday, then I'll update this post.

TBF, I am not very keen on how effective injection cleaners are. I remember seeing a video from "Project Farm" and whilst it did a bit of difference, it wasn't the ground-breaking clean-up one might think of. Regardless, I'll use 100 RON fuel for a bit now, plus I got another can of cleaner to use on my next stop to the gas station.

 

@Quenthel I have a very similar issue (except 3 cylinders misfire), and noticed that 95 or 100 RON fuel don't make a difference at all, I mostly run 100 RON and only use 95 when it's not available and I'm getting low on fuel.

 

Its probably not a bad idea to have an extra plug and coil stashed away. That said, I guess FCP is getting a new order from me today.

 

It’s too bad that most techs these days don’t know how to use an oscilloscope and instead go through the brute force method of removing plugs, coils, etc. and swapping out. Effective, but a wave form on a scope can diagnose the problem more quickly and effectively. Sadly, electrical engineering is the strong suit of the manufacturers but not of the technicians in the field. Most cannot intelligently read a circuit diagram, much less understand its operation. The manufacturers have out-kicked their coverage as we say on the gridiron.

 

I guess that makes sense, but I would need to see a mechanic anyway.

I can confirm that I didn't see anything resembling an oscilloscope at the shop; not sure if the dealership would have one even. My only concern at the back of my head is whether there is a worse problem caused or hidden by the coil and whether I'll be left stranding during my trip back. The coil is definitely bad, since after the swap it lit the CEL immediately, but you (well, I) never know with these rather complex engines.

 

Quick (and hopefully final) update. The replacement coil pack arrived today. €340 (vs ~50 for a non-OE one). The tech replaced it in 10', cleared the saved codes. I did about 50Km; nothing lit up, no codes in Carly either.

I kept the old one as an (expensive) memento. Unfortunately, I won't be getting any money back from Mercedes CH, since I didn't go to the Greek dealership here. Couldn't; the dealership was uncertain as to whether they'd have enough time to fix the issue before I had to drive back to get the ferry to Italy and that would've been more expensive in the end.

 

Isn't a misfire on cylinder #5 mean there's a high possibility of cylinder scoring?

I don't want to alarm someone for no reason, but my understanding is that's the one that tends to get scored and throw random codes?

 

If it followed the coil and when he changed the coil and it went away there is no reason for him be be alarmed by your post. Secondly show where there is any claim of the M176 engines demonstrating cylinder scoring.

 

The resolution (replaced ignition coil) is consistent with other vehicle models with the M17x engine, where ignition problems (misfire and CEL solved by coil replacement) have been reported. This engine seems to have similarities with the M275 V12 as it relates to ignition system difficulties, in addition to multiple reports of vapor separator failure (plugging) causing resultant rear main crankshaft oil seal failure. See multiple reports on this site.

 

Thanks for your comment! As another member clarified in the thread, scoring of cylinder #5 apparently affects the M278 rather than M17x engines (so far, anyway).

Indeed. No other codes, the message hasn't come back up so far, nothing else unusual that my mechanic found with a quick glance.

Thanks for the heads up, @chassis. I was completely oblibious to this. I have an appointment with the dealership in October to fix the center console door; is there something easy and obvious I can ask them to check in order to preempt any potential problems down the line, since I'm under warranty?

I know that if it's something that's too much work for them to check (e.g. remove engine parts) it's going to get them to do it without cause, but if there's something easy to check, that might be a different story. Thanks!

 

Hello ,

I hope you can see my reply and so much thanks for your sharing .

my 2019 s560 cabriolet now is having the same problem, had 5,8 misfire already and waiting to check the code on next Monday to see which cylinder misfire this time .

my car is only 35k km to now , and already seat massage function gone (gas pump leaks)


Just want to know have you eventually fixed the misfire by replacing coil packs ?

 

Hi Lucas. I did, but confirmed it by switching around spark plugs and coils. It's not a guarantee that you're facing the same problem, but if you clear the problem using OBD2 and it comes back intermittently, there's a good chance that this might be similar to mine it and swapping coils and plugs around may help you pinpoint and confirm it.
However, since you're experiencing other issues as well and two apparently unrelated cylinders misfire, consult with a mechanic that can do a proper analysis of your car, it might be something deeper (I don't think coils should affect the seat massaging function for example).

 

thank you !

I realized that my issue is not the same with yours , instead it is very similar to another owner’s s560 , different cylinders were misfiring, so I guess much worse .

fingers crossed that our tech will be able to address it .

 

I have a 2018 S560 and had a cylinder 8 misfire. The Merc Dealer mechanic checked the plugs which were okay and then switched the coils in cyls 7 & 8 to 5 & 6 to perform a coil test to be able to replace under the coil extended warranty. A month later, I again had misfires but this time in cylinder 7. Took back to Merc dealer and they said it was a leaky fuel injector which is now getting replaced. It looks like both coils and injectors are an issue in the M176 engine even though I haven't been able to replicate coil misfires in cylinder 5&6 (which would indicate a coil issue).

 

Barry ‘Putting it on the scope’ went away with modern coils on plugs ignition.

Back in the day (bad old days!) we had easy access to coil positive and ground to plug into. (One coil for all cylinders) Monitor #1 with an inductive sensor (like used with a timing light) and the o-scope could make patterns for each cylinder running. Presto! We can monitor all cylinders at once. Made picking out a dead hole, weak coil, bad plug wires (remember those!), dwell angle ect. Knowing the firing order and where #1 is the mechanic could point out an issue in a particular cylinder. Worked well with limitations. We couldn’t take that guy on a test drive with the CRT (TV) monitor and the thing was big enough it was mounted on wheels to roll around the shop. Back in the day it got used often as car owners could count on going out to the car once to several times annually and have it not start, run poorly ect.

Today every car is equipped with much more sophisticated diagnostic tools. Engine management is forever attentive and can point out numbers of misfires in which cylinder(s).. in many cases at which speed and load point the cylinder(s) misfire. There is no plugging into each coil to monitor it’s pattern. We plug into the car... it says ‘trouble for cylinder #’ and we move the coil from that hole to another (keeping notes where) the spark plug to a different hole (again notes for where it went). The failure follows the plug, coil or injector. Injectors being least accessible stay in place. Modern engine management will tattle on a coil with an open circuit, incorrect resistance or short to ground.
Same for injectors and every other sensor used. Fuel pressure is monitored as the ECU tells the fuel pump to make X PSI of pressure for Y load. Air filters are monitored in certain models as plugged filters... effects air fuel ratios.
Spark plugs now live to 100,000 miles in certain cars. Coils are built bespoke for a particular engine. Everything is a LOT more expensive so we don’t just fire off ‘Points, condenser, plugs, cap, rotor and wires’ as so often happened back in the day. Today that would look like 8 coils and plugs. That will be four figure$. For many of us an expensive shot from the parts cannon.

 

275 being a ‘special case’ in that there are two ‘coil packs;’ each with a dozen coils as a unit with a Voltage transformer to take signals from engine management and tell each of two dozen coils when to fire a big spark as the other coil in that hole fires a small spark to monitor how combustion is happening in that cylinder. The spark plugs switch roles every other firing cycle. Yes; very complicated and expensive when a coil fails as there is no swapping a coil to another hole.

All other engines in the MB lineup use one coil per cylinder. Thankfully the 279 too! Much easier when one fails. Of course when things get old enough that a coil fails one can expect there will be another that fails later.... rinse repeat. This is why many prefer to replace all coils when one fails.

 

The M176 uses one coil per two cylinders. About 9 months later, I haven't had issues with any of the other coils, so I guess that one failed because it was a lemon, rather than old age (the car had about 70K Km at that point, about 85K now).

The lesson for me anyway is that if it happens again, I know what to rule out first.

 

hello I had same bad experiences day before, I was on my way to pick up my client from airport , my car started to shake and suddenly check engine light come on, I attached my blue driver obd2 scanner and givers code for misfire cyl 4 , then I call my mechanic he said look like need to replace ignition coil and 2 spark, I got them from dealer and run to his shop, he replaced front of me then we went to test drive, but less then few miles check engine light back and same code same cyl, brought car to mercedes dealer and waiting now

 

This is why as part of diagnosis the ignition coil and spark plug from affected cylinder get moved to different cylinders. Misfire moves to cylinder with coil? We know what to replace. Misfire is in same hole? Next up for a suspect is the fuel injector. All of this assumes the misfiring cylinder has normal compression.