Hapa88

So my wife has a 2017 C300 Coupe with the 2.0L Turbo motor. Lately she's been complaining about intermittent knocking/pinging sound that happens when she does a moderately aggressive acceleration (like getting on the freeway or passing someone, about 3/4 throttle). I drove her car the last week and tried and tried to get it to do it and was only successful once.

It basically sounds like engine knocking to me. You get on the accelerator and it immediately starts to sound like rocks are flinging around in the motor. As soon as you let off on the gas, and get back on it the sound goes away. Has anyone else had this problem?

Couple of notes: Car is a 2017 C300 Coupe, 2.0L Turbo motor, about 4500 miles. Uses 91 Octane gas (highest available in Tucson, AZ). Tucson elevation is ~2400 ft above sea level. Outside temps around the 80 degree F range. Car is in "Comfort" mode when it happens.

MASSC450

Personally, I'd get the car to a Mercedes dealership ASAP and have them look at it.

That's what your cars warranty is all about.

GerritKw

I would also check wich octane number she filled the car with and what is specified. A too low octane number could cause this also.

applehaus01

Does the engine seem loud in the morning like valves are loose then after few mins it goes away? Kinda hard to describe in writing but almost like a diesel warming up.

Hapa88

As stated, we use 91 Octane (which is the minimum required but also the maximum offered in Arizona).

Hapa88

No, car sounds fine when it starts. It doesn't sound like it needs a valve adjustment, if that's what you're referring to. Everything sounds tight and controlled.

removedCFGaccount

The underlying problem is that wheezing little four: pure crap in my opinion

Mikey53

Mine runs just fine, plenty of acceleration available when needed. IMHO of course.

removedCFGaccount

Makes the world, twirl.

GerritKw

Sorry i missed the octane numbwr. Still that is quite low for European standards.
Here 95 is standard and you can get 98 optionally.
Less then 95 is very hard to find here. I guess the US built cars are adjusted for a lower octane number. Might be the tuning has been a bit critical or the sensor detecting the pinging is malfunctioning.

Hapa88

It's actually the same octane level but the number is calculated differently in each country.
Europeans use the Research Octane Number (RON) standard. US uses the AKI standard which is an average of the RON number and the Motor Octane Number (MON).
For that reason, a RON number will always be 4-6 points higher than the US's AKI number.

As an example:
European 95 RON is about equal to US 91 AKI.
European 98 RON is about equal to US 93 AKI.

GerritKw

That is good to know, thank you.
As mentioned also, this looks like a defect then.

removedCFGaccount

Gosh, I'm sorry. The problem is the engine. It simply can't be made fully smooth.

There are many inherent design limitations which can only be mitigated or concealed. http://www.nytimes.com/2010/08/15/au...es/15FOUR.html
http://wikicars.org/en/Straight-4_engine

You can't make chicken salad out of chicken ....

Thlian

This might be poor attempt to put out a fire with gasoline, but what is your freakin point? It's useless! Because you don't like the number 4, doesn't mean i automatically will break. I have a four cylinder car, you know why? Because having six or more would have ment I had been a milioneer, but I'm not. So apologize to everyone less fortuna than you and stop bombing threads with useless piece of crap! Have fun but don't intensionally insult people.
​​​​

dieseldoc

I have 2 4 cylinder Mercedes and a 4 cylinder Audi. I am pleased with all of my cars. They are not pieces of crap!

removedCFGaccount

Diversity makes the world go. I had my last one years ago. Your mileage may vary, as will the commentators' opinions. The laws of physics don't have feelings.

Hapa88

Thank you for that. You could of given us help, but you've given us so much more!

removedCFGaccount

It's a fact I can't change: the design is inherently rougher.

Mr. J

That's completely true, it will be rougher than a 6 or an 8. It shouldn't ping or knock though. I just drove a C300 loaner 2 weeks ago while my 450 was in for service A and a tire swap. The C300 did sound like a 4 banger for sure, but there was nothing in the engine note that resembled knocking or pinging at all. It just sounded like a high-strung turbo 4.

Happa, either you or your wife accidentally got a tank full of 88 or you have an engine problem. If I knew for sure that the fuel was good, I wouldn't hesitate to take it in and request that the tech ride with you while you demo the noise for him.

marmutz

I have the same problems.. it only happens in the morning first hard acceleration.. problems solved after i change fuel.. i usually use Shell 95.. and change to Pertamina 98 or Total 95 ( thats the fuel brand in my country )

i m drivin w205 c250 2015..
definitly about the quality from the fuel.. strange knockin happen only at first hard acceleration..

Shadow5501

I have head this sound in loaner c300 sedans when getting my car serviced. It's normal noise for a direct injected engine. Kinda sounded like the engine was munching gravel when overtaking. DI gasoline engines all sound a little bit like an old diesel. It's the trade off for the extra efficiency of using direct injection. I have a Ford with their 2.0 turbo DI engine. It's a bit more diesel sounding at idle and quieter in the midrange, but makes similar sounds as the MB motor.

Hapa88

I would completely disagree that it is normal noise for direct injection. I have a 2008 Mazdaspeed 3 with a 2.3L Turbo Direct Injection engine with 118,000 miles and it has never made that sound.

Hapa88

While I agree it's rougher, it does not explain the intermittent pinging/knocking that causes it to be rougher for a period of less than 2 seconds on hard acceleration. Like I said, it doesn't happen all the time.

Over a 20 minute drive of me constantly hammering it off the line or hard passing, I only experienced it once when I drove it.

I'll quadruple check with her to make sure she's using Premium gas, because that was my initial thought as well.

removedCFGaccount

Many compromises went into the design, which, if not fully in concert, make some more obvious than others. Mercedes did what it could, within the limits of known engineering principles.

cenzo86

Can you take a video so I can hear some audio of the sound? Most modern direct injection engines do have a very constant ticking, like a sewing machine during idle. The ticking is from the high pressure injectors. Your engine is designed to run on premium, but if lower octane is detected, the car's ECU will go into knock protection mode, lowering power output to prevent detonation. If you are experiencing detonation your CEL will go on.