Hello all.
I have recently purchased a E400 coupe, M276 engine 3.0L biturbo (333hp). It has 215.000km on the clock.
I posted this in the corresponding W207 forum, but as the engine and most of the car is similar for sedan E400, this may be a common problem to W212.

The car pulls great, runs to redline with no problem, etc. The issue is that it has a loud "scratching" or "metal rubbing" noise during cold start. I will try to describe it as accurately as possible:
- The noise appears around 2 secs after the engine is running (so it sounds normal for that 2 seconds and then the noise appears), lasts for 1 minute or so and progressively quiets down.
- It is not a tapping noise, more like metal rubbing or similar.
- The above two caracteristics make me think that it is not related to a discharged chain tensioner, etc.
- If, when warm, I stop the engine and I restart it later on, it doesn't sound that bad (not sure how much stopped time it needs to do it again). So probably temperature related?
- When it is present, the noise varies if I tap throttle or if I change engine load by setting the transmission from P to N, for example (while braking). Car not moving (that rules out transmission axle, rear differential, shafts, etc. I guess)
- I have checked the heat shields around the exhaust, exhaust joints and supports, tapped catalytic converters, etc. and couldn't find any visible problems.
- I don't know how bad the engine and transmission mounts are, I suppose they will be worn but I don't know if that would justify this noise, specially when it disappears or quietens down quickly and is about normal when warm.
- When warm and driving in town, the car still occasionally makes some noise specially in partial load, you can hear that with the windows open, not inside. Probably due to turbo wastegate flaps, but that seems to be a different issue.

After warming up, idle is about normal, to me it sounds like a V6 diesel, but I suppose that's due to direct injection.
If anyone with same engine can share his experience, provide some ideas, talk about the cold start behaviour, etc, that would be very helpful. Thanks!!!

 

Record the audio please, of the said : a loud "scratching" or "metal rubbing" noise

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The serpentine belt tensioner and the two pulleys are not very robust if owner like doing WOT redline, just so you know....it may be the source of those noise.
You have the aftercooler blocking the two pulleys, so its not an easy sight, more so the RIGHT side of the engine pulley, the 1A.




Other possible noise is coolant mechanical water pump and alternator.
AC compressor will be the last one.

All above mentioned are the spinning devices/component on the engine.
If your serpentine belt is not genuine, you may get some kind of noise.
I read it is about such belt is designed for both sides surfaces use, vs single surface use.

Example the water pump plastic big black pulley is using the reverse side of the sepentine belt, the flat one , not the tooth side.


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Low mileage life for my 2 pulleys and 1 of tensioner. Its not making any noise, I just don't like it when it is not perfect spinning straight.
https://mbworld.org/forums/e-class-w...ng-torque.html
https://mbworld.org/forums/e-class-w...ew-vs-old.html

 

Thanks, Prihadi.
What really puzzles me is the fact that the noise starts a couple of seconds after the engine is running, that leads me to believe that it can't be related to serpentine belt (and also, it sounds more at the back or below the engine / transmission).

IMHO, it must be related to some system that activates with some delay after engine is started (EGR, timing advance, etc.) To discard this, I disconnected the wastegate vacuum pipes just to check if the noise started because the wastegates close (with some delay as vacuum is built), but the noise was the same.

I definitely need to record the noise carefully and upload it here, so you can have an idea.
Unfortunately this engine is very complex and tight so is difficult to have access to many parts, not like the good old M113, for instance.

 

Sounds like the Secondary Air Injection (SAI) air pump coming on briefly with a cold start to get the cat to operating temperature more quickly. Maybe a bearing in the pump.

The pump is probably electrical and not dependent on engine speed or serpentine belt.

EDIT: It appears the M276 does not use an air pump.

Maybe the A/C compressor? There is usually a couple second delay after the engine starts for the A/C to kick in.

 

Thanks. Also thought about that as I had a similar issue in a M113 ajd M72. And replaced the SAI pump.
in this case, first, the M276 engine doesnt have one, and the noise changes when you touch throttle and disappears gradually.
AC compressor, I can definitely check it, but I doubt that it is that, for a number of reasons.

Will continue investigating. Something related to torque converter or transmission, perhaps?

QUOTE=JettaRed;9065783]Sounds like the Secondary Air Injection (SAI) air pump coming on briefly with a cold start to get the cat to operating temperature more quickly. Maybe a bearing in the pump.

The pump is probably electrical and not dependent on engine speed or serpentine belt.

EDIT: It appears the M276 does not use an air pump.

Maybe the A/C compressor? There is usually a couple second delay after the engine starts for the A/C to kick in.[/QUOTE]

 

Yes, that is reasonabl3 and had that issue in M113 and M272 engines but this one doesnt have SAI pump.
I also doubt it is the AC compressor as it also happens when climate is off, but will have a look at it because some cars activate the compressor for a while at start. However, it doesnt sound like it is in that area...

 

Hi guys. Here is the promised video file, I hope you can listen to the audio.
Please note that the noise suddenly appears approx 1-2 secs after engine start up and it gradually fades away.

 

Very difficult to hear, because ur exhaust is no more standard and very loud.

01. Do place the mic at engine bay, have someone start the car for you.

02. Do not do recording in such a place where echo from the building make your exhaust even noisier.
Get a more open space, but not noisy of traffic.

 

Oh, yes, my exhaust IS STANDARD, in fact it doesn't even have the rear fancy tails, but the two standard pipes pointing down.
But it is true that the noise is reflecting in walls, etc. and it sounds even louder. I will try to make a better recording.

BTW: I had the TSB coding applied yesterday and I have to confirm better, but I think that the raspy noise when traveling in the city is no longer there (once car is warm).

 

Wow, standard exhaust.....or maybe because yours is W207 which is a Coupe. Maybe you get sport exhaust ... ? Can't be leaking exhaust right ? I mean you would know

Mine sedan, there is zero exhaust sound up to 3,000 ish RPM..... as it should, being a 4 door.

 

Well, remember it is cold, when warm it is much quieter (still some diesel-like sound at the engine at idle). It is not a sport exhaust, I doubt it is different from Sedan.
Yes, the issue could still be from the exhaust, have to do a proper check WHEN COLD (when warm I couldn't see anything wrong with engine running with the car on a stand and looking under the car)

 

That kind of sounds like the chain rattle to me.

 

Thanks, I understand that the audio is not too clear due to the phone recording it, reverberation in the walls, etc. but to me it does not sound like chain rattle (in fact it doesn't sound as a rattle at all).
At this point I really don't know where it comes from but after replacing engine mounts I expect to have more information.

 

Hi all.
I already posted this in another related thread, but it seems that we have found the cause of the rattle noise at cold startup. The left catalytic converter seems to be loose inside.
I am looking for alternatives but the most reasonably priced one seems to be sending mine for repair (they exchange the core/s by default, they don't "tighten" or repair the existing ones, although I am sure it must not be very bad, as the noise disapperas when hot).
Anyway... does anyone know whether these catalytic converters have 1 or 2 cores inside? There are two O2 sensors, one at the front pipe of the catalytic converter, and another in the middle of its large section. Must I assume that there is one core before and another after the O2 sensor? The repair price changes (the expensive part is the core, around 250 euro each).

Unfortunately it is difficult to get a replacement part, too few 400's here, and only the W207 are equivalent, not even the W212, at least for the left side (which comes as a single part until the middle muffler, stupid design!)

All information will be welcome.

 

Based on mine E400 W212.065 M276.820 , it is 2 core.
Engine---->>>Core 1 and the rear or 2nd 02 sensor hole in the empty middle and then core 2


Boroscope into the CAT 02 sensor hole. See two cores.


I cant remember which photo below is front or rear core, sorry.



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2018 archive for below:

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Many, many, many thanks, Prihadi for your photos! They are extremely useful to me!
That confirms that you have the same exhaust setup as mine, with that stupid distribution of left catalytic converter plus middle muffer in a single piece, while the right one can be separated. Why??? stupid design.
I have found a company here that can repair mine for around 550 euro, I don't know if they are fully aware that there are two cores inside, I will make sure to avoid surprises.
Why did you disassemble your exhaust and examine your catalytic converters inside? Did you have similar issues with them?

Thanks as always!

 

Indeed, I have always wonder WTF was the engineering thinking when they/him decided to do that ? Why why why ?
It is extra leak point if only one side, if both sides at least I have greater flexibility when removing exhaust system.
Must be some real good "weed" beside the drawing board of the engineer.

 

Yes, estupid design. The CLSs, C, etc. of that age, with same engine, have fully removable catatytic converters, however.
I am asking in some shops around to try to get a reasonable quotation for the operation, but first I will put the car on stands and make sure myself that it's only the left catalytic and that the failure is clear, as the operation is not cheap and I don't want to throw the money to the dustbin as I did with my engine mounts, and also don't want to be repairing the right converter next because it is also bad. I have already invested good money on the car.

 

Good luck on the repair.

 

So absolutely no benefits of this design?

 

Come to think about it.....
Maybe that single joint its for vibration control, like resonance control thingy. Maybe. MB wont waste money for no reason.
That extra joint cost $$ in fabrication, gasket and the unique clamp.
Exhaust systems are tuned to be smooth in the vibration sense.

There is a rubber with weight on my exhaust as vibration damper. I am sure all W212 get this.

 

Hmmm, I mean if true then makes sense, being an E class.

 

Well, I took the car to a Catalytic converter expert. I already had a quotation by phone to repair it there, but when I took the car there to make sure, the guy was honest and he said that the sympthoms didn't match his experience: a loose converter core doesn't fix by itself when hot, it continues rattling. Also, a loose core lets some air passing around it without restriction, so it is impossible that the car would pass MOT gas inspection, as it did. He recommended NOT to replace or repair the catalytic converters without further inspection.
He lifted the car and punched the cats a bit (hot, that's true), and he couldn't notice any signs of looseness. So he suggested me to leave the car there one day, let it sit overnight on the elevator and check the noise again when cold, and even remove the middle O2 sensor to put a camera inside and check the condition of the cores. What we DID see was an exhast leak back at one of the joints from the center muffler to the rear section (one of the rings was black all around). So that's the first thing to correct.
On one side, I am relieved that I don't need to exchange or repair the cats, but now, I don't know again where the raspy sound comes from when cold...

 

Have you replaced all of the rubber mounts of exhaust system ?

Our exhaust expands a bit when hot, so when cool it may not "touch" xyz , but when hot it may.

I have replaced all of mine. : https://mbworld.org/forums/e-class-w...r-hangers.html
First half of the video in the post shows how much work the rubber hangers are exposed to.
The video in the post shows exhaust expanding when hot at 1/2 last of the video.

 

Wow! I see in the video that the mufflers progressively go to the rear of the car by several cm!!
I don't see how this can affect my noise, however. The noise, when starting, goes from more or less normal (having in mind the accelerated idle when cold), then suddenly raises after a couple of seconds, and it stays there and then progressively quietens during the next 30-60 seconds and gets even lower after several minutes.