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Looking for some guidance from the guru's. I believe this to be a new symptom on my car.
2012 CLS550 with M278.922 engine (77 000km/47 000miles)
Coincidentally I recently replaced the spark plugs myself and am not quite certain but this noise may have only begun after doing the work. I torqued everything to spec, granted with kinda cheap (Princess Auto/Canada) torque wrenches.
No CEL in the vehicle, no messages on my cheap bluetooth ODBII scanner. Engine response etc seems to be very good, smooth, no rough idle, no hesitation, lots of power, smooth curve.
The knocking only becomes audible once the engine is quite warm, never when cold, takes at least 15 minutes.
Sounds like it's near banks 5 & 6. I was able to capture it here:
Just to rule it out, I completed another oil change, first ran Liquimoly 'Engine Flush' for a 15min drive, did the change with Liquimoly 5W40 and OEM filter from the dealer and added Liquimoly 'Viscoplus'. No changes.
Any thoughts? Is it something I did? Could an over/under torqued plug cause something like this? If I can't get any answers my next plan is to take it to a knowledgeable mechanic, run a full detailed Xentry scan and then a compression test.
2013 Weistec 540/715 tuned CLS 550, 2008 E350, and '07 Jaguar S-Type R
It does sound somewhat ominous - to me like valvetrain (I can't imagine it would be a rod bearing with that kind of mileage). I would pop for the pro diagnosis on that bank. Hopefully, it's nothing serious.
I've scheduled it with the mechanics to be looked at in a few days. With no CEL light or other indications is there still more info available with a full computer scan that can help in diagnosing or is this going to turn into a trial and error scenario?
Tried getting it into the dealer for a diagnostic.....3 week wait. I'm not that patient so I tried hunting down other reputable options locally. Found a company that had the xentry computer, did a full scan, noise was present every time once engine was at normal operating temperatures, but parameters all appeared flawless. Not a digit out of line including compression. After poking around the engine a bit more, paying them their fee, I am left back at square 1 unless I am willing to begin a complete tear down and start looking at internals. I am reluctant to do so.
After bringing her home I decide you know what I am going to swap the coils and plugs myself from cyl. #5&6 with 3&4 and see if the problem follows. As I begin by removing the coils on 5&6 I quickly notice something very odd:
Now check out the plug from the same cylinder (#5 the exact one I suspected from the sound)
I'm going to put a video together but aside from the burn/charring around the base the porcelain on this plug actually spins! It's loose in the collar and spins freely round and round. So this plug is defective. A video documentary I saw on the M157 engine (AMG version of this one) showed an image that depicted the range or angle the spark plug tip had to be facing towards the valves to perform properly (hence the specific torque of 23nm or 18 ppsi). With this one being loose there's no telling which direction it was facing and it was likely spinning loosely inside while firing!
A fresh plug has been installed and to play it safe, I am replacing the entire coil as well but it's being overnighted so will report back about the results and if my ticking noise is gone by tomorrow evening.
My concern now is what, if any damage or burning has occurred inside the combustion chamber of this cylinder? Thankfully I have only put on a few hundred miles since these plugs were installed and this one was either defective from day 1 or somewhere in between. Should I be concerned? Did I potentially get serious heat and damage in there? I considered spraying a 'combustion cleaner' directly inside before installing the new plug but I had second thoughts about having excess flammable fluids in there and possibly seeping into the cylinder. The dealership provided me with a can of Mercedes branded cleaner to run through the fuel system as well when I went for the parts today. My thoughts now are to just run that stuff through a new tank of gas, and go with the ol 'Italian Tune-Up' method and run the car hot and hard to shake/burn off anything possibly in there.
I can't imagine that a misfiring plug would cause any cylinder damage. A bad plug shouldn't cause additional heat IMHO.
Normally I would agree with that analogy but the bottom of the boot and base of the plug would clearly suggest otherwise! I have also read in another thread about doing spark plug changes and that mis-torqued/misaligned plugs can melt the cylinders! Again not sure how credible that source is though but I did find this reference below on the M157 (AMG version of my engine) SKIP TO 06:49
2013 Weistec 540/715 tuned CLS 550, 2008 E350, and '07 Jaguar S-Type R
So improper orientation of the flame travel creates a severe hotspot at the edge of the piston? Yikes.
Did you notice a difference in torque required to remove the #5 plug?
Here's hoping the fresh plug and coil pack result in a quiet engine
So I completed the repair about 10 days ago and the knocking has completely ceased! Problem solved.
So lesson learned, don't discount an ignition problem as to potential cause of engine knocking.
I had the same issue with a Bosch spark plug which was causing and intermittent knocking noise in the cylinder head area. Spark plug number 4 was burnt like yours and the porcelain was spinning After replacing the plug the noise is completely gone. I also replaced all my coil packs just in case.
Excellent job diagnosing and finding/correcting the root cause of this, "Maduro"!
This would have kept me up at night until resolved.
I learned, a long time ago, if parts were loose and separate at one time, they can be loose and separate again.
Who would have thought spark plugs, but there you go!
04-18-2021, 12:39 PM
