Cuck350

Hello I drive a 2014 C350 m276 engine

Went to a Mercedes dealership 2h away to get spark plugs changed plus a few other things not related to the engine. Come home and the next day there is this chirping noise as seen in the attached video coming from the back driver side. This noise happens when the engine warms up and is RPM related (quieter but faster).

Went to a local shop and they said the noise was coming from there and did nothing to diagnose/fix it just charged me $80 and told me to go back to the dealership. I go back to the dealership and they said they found a vacuum pump leaking and has a reed valve leaking and needs to be replaced for $1200.

I found this video with the same engine and issue talking about a bad vacuum

You Tube

they remove the oil cap you hear a pressure noise and the problem was fixed thus indicating bad pressurization. I tried this on my car and it did not fix nor lessen the noise but there was a very light suction to the oil cap (I think this is normal)

I researched more online and found a few forms here talking about a loose/improper spark plug causing this issue and that's what made sense to me since this issue happened after their spark plug work and the sound is coming from the around around the back driver side spark plug

You Tube

You Tube

I go to another local German automotive shop and they downplayed that spark plugs could cause a noise but they will look. They said the spark plugs were tight (not sure if they checked if they were seated properly) but they do not believe the issue is coming from the vacuum pump and are trying to figure out where it is coming from.

I am now asking you guys what you think this might be from because after 3 mechanics, I am not sure what to do.

JettaRed

iTrader: (1)

That sounds pretty bad. If it happened immediately after servicing, I'd have a conversation with the service manager and then MB corporate. What vacuum pump is back there and what is its purpose? Changing the spark plugs is a labor intensive process that requires removing the intake manifold. The plugs also require torquing to a very specific setting. I know because I have done it on my 2014 C350.

If I remember correctly, there are some vacuum hoses that need to be temporarily disconnected. Also, there are seals between the intake manifold and the head (see green seals in picture) that must not be pinched or misplaced. Not sure if that would cause the noise, plus I would think you'd get a CEL due to unmetered air entering the engine, but suddenly a leaking vacuum pump seems very suspicious.




Mercedes Ignition Service Kit - Bosch 0041598103 | FCP Euro

JettaRed

iTrader: (1)

The torquing of spark plugs for the direct injection engine is to insure proper positioning of the ground strap. If not positioned correctly to the high-pressure fuel injector, the engine could be damaged.

Odd Piggy

That’s definitely not the crankcase vent valve noise, and your finding of minimum vacuum at the oil filler cap bears that out.

I didn’t remember the non-turbo versions of the M276 even having a vacuum pump for the power brakes, but there is one listed for GLK350 2012-2015. So maybe. It’s a $535 part at dealer prices. But there would be a vacuum line from it to the brake booster that may be the source of the noise. Ours went 155k miles without so much as a peep from it. Try disconnecting the brake booster line with the engine running to see if the noise goes away or changes pitch.

The spark plugs would have to be very loose to cause this noise.

ctf011

Hi, did you ever get to the bottom of what the noise was coming from? I am having the same exact issue right now. Sounds like it's coming from the vacuum pump area.

Cuck350

The issue was a vacuum line from the vacuum pump to the intake manifold. The side that attached to the intake manifold was torn/cut which ultimately caused the noise. It is a hose that is to be dethatched when working on the spark plugs so that explains why it happened after the spark plug work.
-1 for the MB stealership for severely misdiagnosing my car and trying to charge $1200 for this issue and $700 for another issue (that other issue was only a $150 fix) when this noise issue was like a $10 hose.
+0 for Volkswagen because they did find what was wrong with my car but in the process they messed up other things leaving me without a car for a week :/

TimC300

It does look like a pain to work on.

Moto_Guzzi

These wild European over engineering trend of vehicles has to stop, look at how much money & resources were wasted for a simple issue.

ctf011

Wow, thanks! Just found that mine has a cut in that same vacuum line as well. Hope no further damage was done.