This has happened several times during my commute. Wondering if anyone has any idea what might be about to break.. I'll be cruising along at highway speed and go to pass someone. I press down on the accelerator (nothing crazy, just to speed up enough to pass), and the motor stutters, I hear a clack clack clack coming from what I believe to be the underside rear of the car, followed by a puff of black smoke being emitted from the exhaust, then everything normalizes. No CEL. This is on a 2009 automatic with about 50k miles on it.

 

Justa or MCS?

 

It's an 'S'

 

Start simple and work your way up. Change fuel supplier. You may pay more, but you could be getting a BS mix. More than a few change artist out there. Check the air filter. Its a low probability, but it isn't a big ticket fix, either.
It is getting close to spark plug time at 50K. You might want to go ahead and swap them. I know, you would expect to detect a plug failing a little different, but, maybe direct injection engines act a little different. Who knows?
After that I would be taking it to a techno-whiz and getting him to do some of that computer voodoo. I just don't have enough history with that stuff.

BTW. Most of them whiz kids couldn't set the points on a '69 327, either. They just weren't raised with it.

 

Sounds like a case of R56 superknock to me.

Check out the info contained in this thread:

https://www.northamericanmotoring.co...eration-3.html

Your symptoms appear identical to many of the reports therein.

 

I agree with Gil-galad. Superknock is most likely what you are experiencing. When it happened to my 07 MCS there was no engine light but there was a code stored that the dealer detected. I'm not sure if a off the shelf scanner will detect the code as it is most likely a "Pending" code as it is not frequent enough to illuminate a light. Finding the cause is the fun part. Bad gas was mine.