S-Prihadi

See if your s-park plug tool lacks the top side gripper, some uses rubber insert as gripper to prevent spark plug from not being centered.
Below is a simple but good video , where the ceramic may crack

E350-FR

Hi everyone, my W212 E350 does exactly the same sound. This model was not sold in France (it is a German import) so the mechanics here are not use to the M276 and they just suggested me to replace the motor (because they suspect a rod issue)....
@Geep 250GD @2015-E350-Wagon do you confirm that after the spark(s) replacement the knocking sound is gone? (it should be cyl #2 for me as I had a few sporadic misfires here in the past)
Thanks!

2015-E350-Wagon

Yes. In my case, replacing spark plugs solved the sound / issue (as described). I’ve run the wagon another 2-3k miles since. No issue

E350-FR

Thanks for the feedback ! At least, given the price of a set of spark plugs against a brand new engine, it worth trying

E350-FR

The issue was the spark plugs (two in my case, cyl #2 and #3) !
Engine sound before:

Engine sound after:

And here is one of the plug in question:

I suspect that the torque (and so, the index/orientation) was not respected by the previous mechanics...

Thanks again for this thread, it saved my engine (!)

CaliBenzDriver

Thank you for these great video.

That failed sparkplug is really something to see it slide up/down!!!

Overheated ignition coils and boots are known to require replacement to prevent misfirings.

E350-FR

In addition, I found that (kinda scary) recommandation from Mercedes about SP indexing on direct injection gas engines, including m276...