Hello all.
I have recently purchased a E400 coupe, M276 engine 3.0L biturbo (333hp). It has 215.000km on the clock.
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!!!

 

Sounds like the oil check valves for the cam shaft chain tensioners have gone bad. Similar to other MB enignes, the cam shaft chain tensioners are powered by oil pressure , there are check valves in the galleries that are supposed to maintain pressure after the engine stops. There are huge threads on here regarding this including MB recalls to rectify the issues.

Best advice is to get this checked out ASAP. If left alone, other issues can crop up including timing issues, poor running , check engine lights even loss of oil pressure to the main oil galleries with catastrophic bottom end results.

You might also check into the oil pressure control solenoid thread ...the ECU controls the oil pressure via the oil pressure control solenoid to reduce drag from oil thereby allowing MB to improve gas mileage and use lighter weight oil. ..AND ....that goes bad with severe consequences....

 

Thanks for your help!
To be sincere, although I have read about that issues with timing, too, I tend to discard that, because:
a) In the TSB for installing the check valves and revised tensioners, they all fall well before the serial number of my engine, so that's supposedly corrected in mine.
b) The noise is not tap-tap-tap, but more a rubbing noise, varies with load and disappears progressively. I have listened to other videos about the problem you mention and sound different, more like a ratchet for some seconds.
c) The engine sounds normal for 1-2 seconds when I power up, and then starts making noise. If the tensioners were discharged, that would not happen IMHO.

 

Most likely the wastegates. Try to remove the vacuum line to the wastegates before you start it next time

 

Thanks! I already tried that, no change. I even forced them closed with a vacuum pump before starting the engine, no change either.
However, relating to this, I also have some wastegate noise at partial load. This afternoon I will get the car to the dealer to apply the infamous TSB which "cures" that issue by means of SCN coding. Will comment on the results.

Returning to the cold start noise, I am starting to suspect that it may be either transmission related, or exhaust related. When I lifted the car to do an oil change, I inspected the exhaust line and saw one of the brackets at the rear before the silencer had been replaced, while the other was not. At that time the car was warm so no noise, but perhaps during cold start there is a leak in the one that was not replaced. I have to get under the car when it is cold and make someone start it while I listen.

Parts 412 / 415 in this diagram:
https://www.ilcats.ru/mercedes/?func...=4&language=en

 

I would suspect motor mounts causing whatever to make noise. Mine caused the left tail pipe to make a nasty noise as the cold idle freq resonated it.
You can do a power brake check to see how loose the mounts are. Otherwise you can record and post the noise so we can get a better feel for it.

 

Thanks. With 215.000km on the clock, the mounts must have known better days for sure. So they are next in my list. This weekend I will first replace transmission mount, I expect some improvement there in vibration and feeling, but the engine mounts are next.
I tend to think that this particular cold start noise is not caused by bad mounts because it disappears in less than 1 minute or so, but who knows?
Also, to me it remains unexplained why the engine noise seems clean for 1-2 secs after engine start and then the nasty sound appears. My engine mounts are not active, btw. I have learned that some diesels have electrically controlled pneumatic mounts to become softer then during crank and engine stop, but this is not the case as this is a proper gasoline engine :-)

Thanks, guys for the replies, it means a lot to me not to be alone in this investigation.

 

Imo it's the way the eng idles at cold start. It goes through steps, so the first 30 sec or so is extremely retarded spark and high rpm, then it will transition to normal spark but it may take a little longer if it's colder. Rpms drop slowly as it warms up and mine was resonating the tail pipe during a specific rpm range during that time. Once warm it runs smoother so it wouldn't resonate at that rpm again. When I pulled the mount it was obvious it was metal to metal with the mount support bracket :o The mount and bracket are very close so it doesnt take much to hit. Of course my idle, rez freq and whatever parts make noise will be different than yours, but if it's going to vibrate anything I think that cold idle is when it's most likely.

 

I had that done too and I did not make a difference. For me, removing the cable for the oil solenoid made a big difference in the way the car responded at low rpm’s. Did you check out the vacuum pump check valve?

It would help if you can post a video with the sound. Maybe you can lay down your phone under the spot you suspect and start the car.

 

Here is the video I promised. I hope it can be heard. Please note that the noise increases after 1-2 seconds from engine power up, and it gradually lowers.

Another update: yesterday I had the turbo TSB applied at the dealer. I have to test it a bit more, but it seems that the noises from the wastegates when traveling slow in the city, etc. have disappeared. The cold start noise unfortunately remains.

 

I can't tell fom the vid. The spark timing in the first couple seconds is more normal btw, to fire it up, then it goes extremely negative as mentioned, which is "cat heating mode". As an experiment, if curious, you could try putting it in gear which will lower the rpms and change the freq. I'd imagine the noise will then stop. I'd assume spark is still very negative in gear but I can't recall ever checking it.

 

Thanks. The information you provide is quite useful to me and gives me an idea.
Perhaps I can do a test: locate the engine coolant temperature sensor (I assume that's what the ECM uses to determine that it's a COLD start) and provide a false reading by connecting a fixed resistor to fool the ECM and make it think that the coolant temp is, say, 50ºC (so "warm" start).
If I am correct, that will void the extreme cold start timing and higher rpm, and if that doesn't produce the nasty noise, I can maybe discard mechanical damages (chain slack), lack of oil somewhere (chain tensioners, transmission, crankshaft...) and think about a minor exhaust, etc. issue. If that's the case, I can try to find it or simply go to a remapper and ask them to modify the cold start maps.
What do you think?
Any information about the temperature / resistance curve of the engine coolant temp. sensor would be very helpful here. I will try to determine if it's accessible, too, as it seems to be at the back of the engine.

 

I was just giving my opinion on why it's making noise at that specific time. Imo you simply have some part somewhere that is making noise because of it. Like how my tail pipe was, which never made a peep until the motor mount died. So I would replace the mounts first, but you could also find whatever is making the noise. Eg; my tail pipe went silent when I pushed it a bit to the side.If I wanted it to stop altogether I would probably kick the muffler really hard. Yes that's redneck, and yes it works. So my guess is you have some part, that if tightened or smacked with a hammer, or bent a bit, would stop making noise, but you need to find it.
And yes you can change the rpm and spark timing to fix it as well, because I changed mine. I did it because it's too loud on start, and not good for the engine. It also cost me ~$900 for the hardware to program it. I would not try to tamper with the sensor, for tew reasons: One is that will upset normal temps unless you use a switch to turn you hack on/off. Two is it uses the O2 sensors because the point of the obnoxious cold start is to heat the cats, so it's the cat temp you'd need to trick. The end temp hack will lower idle when not in cat mode, but will it do anything during cat mode? It may also trigger a check engine light. It's a lot of work to find out, so if it were me I'd swap the mounts and/or find the part making the noise.
Fyi the hardware I use to program it is HP Tuners, which is 800, and I wouldn't use that until I backed up the ECU, which I used KESS for and is ~60 bucks. The software for each is free. Btw I didn't buy that to adjust the idle, but it can, so I did.

 

Thanks for your thoughts and sharing your experience.
I mentioned the coolant sensor trick only for a test, just to have all things at the same temperature as when cold, but making the ECM avoid the warm up cycle.
Anyway, my next item in the list was already changing the engine mounts, so after that I will investigate further.
Today I have let the car cool down a bit, and at at 60ºC it started normal (low idle) and didn't make any strange noises. Will go down to see how "cold" it can be without noise and without warm up cycle in the meantime.
Of course I'd rather fix the rattle than void warm up cycle, but if I don't find it I will definitely go to a tuner that, here, for around 350 euro can do it for sure (and perhaps give it a bit more boost at low revs :-)

 

Sounds like you like to tinker? I'm hardwired that way and have trouble leaving well enough alone. HP Tuners is awesome for tinkers.
If you go to a tuners shop it might only be 350, but I don't really know. I think most people buy whatever hardware, like a MyGenius, to load the tune themselves, which is emailed to you from the tuner. The MyGenius allows you to revert to stock come smog time. If you go to a tuner in person, then you may need to go back to make it stock for smog, then back again after. The dealer may also wipe the tune if you take the car in for service.
So imo it's better to have the equipment to load tuned/oem yourself. With HP Tuners you make whatever changes yourself, as often as you want, whenever you want. Eg; power, rev limits, speed limits, spark, fuel, reduce temps, reduce turbo lag etc. I even made engine braking much better. If you use a tuner, each adjustment will cost you, and takes time, maybe days. With HP you can drive, stop, make a change, repeat over and over all day if you wanted. A lot was just playing around to see what does what, tinkering, but mosty it was fine tuning misc things a tuner would not normally do. Plus HP is an outstanding data logger to watch live and/or play back later. It would be much more difficult to dial it in if you can't see what it's doing and how it responds to your changes. That's why I know what the spark timing is doing on cold start, I simply play it back, including recordings from when it was stock. I also learned that retarding spark at full load can make more power, at least with my eng and I doubt yours is different. Just something to consider is all.

 

Yessss, I do like tinkering!
It is definitely worths considering, will have a look to the gadget, thanks!

 

I have some updates about this issue.
First, I had my motor mounts replaced. It made no difference at all, in any sense. The old ones looked very nice (and they are 218.000km old!!). So 650 euro less in my pocket. Snif!

Yesterday I took the car to a exhaust garage and had them sit overnight on the elevator and start it up this morning, when fully cold, while they observed from below. They say the left catalytic converter is a bit loose or worn inside and it produces the noise, also noticeable when tapping it. It can be repaired (the core has to be replaced), and now I am waiting to hear the price of that operation, to decide whether it worths the money or not.

At least I am relieved as the issue is not related to engine or transmission internals, timing chain, etc. and driving it shouldn't make any harm (as soon as it heats up, it sounds ok indeed).

 

Given it's age and mileage, that's not surprising. At least you have a baseline now for your motor and tranny mounts, as well as your exhaust.

 

Hello
there is little knock when I start moving the car as if there’s something loose that knocks, it sound s if the knocking underneath the car
the car w214 e400 cope

 

Almomen, ideally you should make a new thread for a new unrelated question, but we're here so here goes:
Ideally include a video so we can see the car move and hear the noise. Even more ideally have one person make the noise, repeatedly, while you try to locate it with the phone recording to narrow down the location.
Plus details like does it do it when moving forward, reverse, or both? Any other time, like speed bumps?
One knock, multiple, constant? Or maybe every time you give it gas from a stop?
How old is the car.
Are you in, or was the car ever in a rust belt?
Noise comes from the front, middle, back? Left, right, center?

My first guess is the motor mounts. You can easily test this with the hood open, hold the brakes hard, and give it a little gas in drive. The left side of the engine will rise up. If you can give it about half throttle and it only rises maybe 1/2" you're likely ok. If it rises up a couple inches then not so much. You can google this and see videos of people doing the test to see the before and after to see what shot out mounts look like compared to new.
If this is the case then the knock sound is likely when the eng falls back down just after you give a little gas, but you just have to do it and see. And of course there are a variety of other things that can cause a knock sound, which is what all the questions were for, to narrow it down.