Hello all. After much searching without finding a similar description of sound and behavior I've been forced to post this thread. I bought a 2011 C63 with 28,000 miles on it about a month ago. The car had just had a new torque converter installed prior to me picking it up so i drove very tenderly and did not pass 4K RPM until putting about 900 miles on the car.
Now that i have been able to open up the throttle more there is an obvious squeal/whine coming front the front underside of the car when accelerating using more than 1/3 throttle. It seems to be correlated to the RPM of the vehicle and begins around 3500 RPM with a turbo-spool type sound and then changes into a supercharger-like whine and shriek at higher RPMs. Sometimes after pulling up to around 6K RPM or above the vehicle will misfire for a few moments and throw misfire codes along with P0171 (engine bank lean) code. After running for a bit longer the car will run fine and not misfire. Sound is only really noticeable when there is substantial load on the motor. The car performs great at low rpm's, shifts are fast and crisp, transmission doesn't seem to be slipping but then again I don't have a properly performing C63 to compare it to.
From the research I've done my belief is that I have a vacuum leak somewhere causing the sound. Intake manifold/gasket? PCV valve? Vacuum lines? Throttle body seal? Leak at a sensor seal somewhere? My only other guesses are Pulley/Bearings? (I did have to replace the battery last week, bad alternator bearings?), Belt tensioner, clogged cat, or possibly sound from transmission?
I'm really bummed about this and will greatly appreciate any input or ideas pertaining to the problem/solution. Thank you and happy new year.

 

I was gonna say sounds like an air leak. My guesses would be the intake mani gasket and/or PCV. I had to have my PCV replaced due to cracks at about 60k miles.

 

That's insane, same noise I heard from mine when pushing it. I first I thought it sounded nice because it sounded like a supercharger but then I started scratching my head because I don't have one lol. Also had misfires prior to this and had low pressure fuel system code thrown.

 

I plan on getting both checked this coming week.

 

Fuel pump maybe? That could explain the lean bank code.

 

At this point I don't even know. Been having misfires and shaking for a while. Had the car checked and it's only throwing a circuit short for o2 sensor but it hasn't gone away. My mechanic thinks it may tune related because all sensors were turned off after removing my sec cats. So I might have to flash back to stock

 

Apparently my car has some kind of tune on it but the previous owner never stated which tune when he traded it to the dealership. How can I flash the tune to stock?

 

Dealership can reset your ECU.

 

Thanks I will get that done to see if it helps, but because of the sound I know that there is a mechanical or vacuum problem somewhere.

 

After taking a closer listen to the car while revving in park and neutral today, the squeal sound is definitely audible. That rules out the transmission I guess.

 

I think you guessed right. You have a vacuum leak. That lean fault code P1071 confirms it + the sound. One way to troubleshoot would be to clean your MAF, reset properly your airboxes and see if the sound is still there. Also check for cracks in vacuum lines around your PCV. Finally you can spray carb cleaner or MAF cleaner on top of your intake to see if you notice rpm changes in idle. GL

 

Interesting thread, I have heard a SC type squeal on my 2009 since I got it in June. It had 13k and currently just 17k on it. The whine is noticeable in park or neutral as I too thought maybe it was the tranny. I have replaced the pulleys, thinking that was the next culprit, still there.

I'll ask my tech about vacuum leak the next time it's in (soon for rear tires I have coming). It does NOT misfire and has not thrown any codes at all thus far.

 

Ok here is another clue to the problem;
Whenever I fill up the tank to "Full" within 5-10 minutes of driving the car will stumble and misfire in an obvious manner but only below 3,500 rpm. After a few more minutes of driving the car runs fine. Could this help to point towards a certain issue?

 

happens to my car too ..it's been doing it for 2-3 years now..always after i get gas, then it stalls sometimes too...Honestly just accept it, I've replaced pretty much everything remotely possible, new intake manifold, entire new fuel system, had them smoke check for leaks, new purge valve etc etc..you name it i had them look and replace it ..i pretty much have a brand new top end because of it and it STILL has the issue.

I think it's mainly to due with the cars ECU file / or tune and it being "Winter" because the car rarely will do it in the warmer months

 

Yea I've come to accept it because it happens every winter. I may reset the ECU and see how it goes for the rest of the winter.

 

So maybe this initial full-tank misfire is unrelated to the sound that I'm hearing.
This has been like a murder mystery

 

I'm going to purchase a handheld from OETuning and reflash it to stock and see how it works

 

i hear a whine too but it's from my AUX cable that comes out of the glove box..sometimes the male end thats in the car is touching something and sounds like a S/C

w204nyc - when i do that it runs worse but then again my car has no cats so the ecu is looking for o2 senors that arent physically there ..i was just reading on the forum about the "winter" blend vs "summer" blend and i think it has some truth too it because every year around the end of October i always have to put a off the shelve tune on (OE or EC) otherwise my custom tune just runs like *** for 4-5 months when its cold.

makes you want to find the cause though or atleast figure out why, seeing as its happening to quite a bit of the cars it seems like.

 

Same issue with me. I have no secondary cats and the O2 sensors keep tripping looking for them. For me it usually happens after I drive the car, shut it down and drive it an hour later. That's when I get all the misfires.

 

Ok guys so there were some revelations today as to the cause of the misfiring, sound, and other strange behavior exhibited by the car. As I said before, the car had some kind of tune on it, I now believe that said tune was the cause of the misfiring and strange driving behavior. I took the car to the Eurocharged headquarters here in Houston today and purchased the MyGenius along with the tune. After flashing on the Eurocharged tune, the car immediately runs smoother, the throttle response is more consistent, and there have been zero misfires. My MPG average has increased from 12 to 15 so I believe that something with the previous tune was really not right at all. Possibly too much advanced timing?

Now about the sound, while at Eurocharged I described and demonstrated the sound the car was making to Phil. After pulling back in we popped the hood and took a look at the pulleys; sure enough one of the pulleys was wobbling and had the paint rubbed off in places where the belt has been slipping and rubbing due to the wobble. I now believe that this is the culprit of the supercharger-like sound. I will be replacing the pulley later this week and will let you guys know if that solves it!

 

Interesting! At least the fix cost you just a tune!
What tune was originally on the car?

 

Interesting! Glad EC were able to sort it out.

 

I tried with OETuning and they told me I had to purchase a handheld for $200 plus a tune on top of that. Seems unfair for a previous customer

 

Mystery tune! I was never able to get that information. I'm guessing it was sloppily tuned somewhere.

 

Now my concern is getting the dealership to pay for the new pulley(s), belt, tensioner, and cost of install. It's been making the sound since I picked it up from them so I believe they should have been responsible for fixing this before giving the car to me.