Wife's 2012 ML-350 with the OM642 did something really strange. On first startup today it started knocking, with a moderately heavy knock you could clearly hear over the normal diesel sound. I had her pop the hood and I took off the plastic engine cover. I quickly isolated the sound to a silver (aluminum) colored part on the top left of the engine (see attached pictures, the pencil is pointing to the part) I put my hand on the part and could feel it rapping internally in time with the knocking sound.

After the engine ran about 3 minutes the rapping and knocking sound became intermittent, and 5 minutes after starting the sound and internal rapping were both gone.

Can somebody ID the part in question, and tell me how difficult and/or expensive it is going to be to replace it if it keeps acting up?

Many thanks

Attached Thumbnails

   

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Doing some research, it appears the part is the vacuum pump.....can anyone confirm. I'll ask the question in the ML section also. Thanks

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

That is indeed a vacuum pump, however are you sure that is making the noise? Those pump are very simple in design and rarely fails with low mileage.

If you want to check the pump noise better, carefully (oil will filing out from the timing chain) with the engine running open the oil filler cap, you should hear the vacuum pump deep tapping away (its normal), however should not knock as you describe.

Heres a normal vacuum pump sound with the oil cap open and engine running
https://www.youtube.com/watch?v=3cxAyOa0m94

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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

Yep, that is what is definitely making the noise.......and I was able to feel it rapping when I put my hand on the pump while it was running. Funny thing is that with the hood of the car closed it sounds almost like the deep sound in your video, except it was a sharper and louder knock. The wife also said earlier today that the HVAC system in the car was acting a little flaky at times and apparently that is vacuum controlled.

__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

when you have a vacuum leak they will make the noise you are describing. What did you find?

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2014 GL450 76K - Wife's DD
2013 GL350 123K - My DD
2002 ML320 300K hard miles (workhorse)
2001 Z3 105K the 4 weeks a year ride
1995 E300D 189K - Rarer ALL options one ortho seats & all

Past ones
2015 XC70
2008 V70
2003 XC90 2.9 (POS)
1998 Wrangler (sporting a SBC 388)
1995 E300D 500K - Should have kept it!
1985 E300DT
1984 E300DT-T
1984 240D Gray market

It was indeed a failing vacuum pump. Put a new pump on (fairly simple) and the issue went away.

__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)