Engine Mount Replacement, Exhaust Issue, CEL
Thread Starter
Newbie
Joined: Apr 2024
Posts: 2
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2011 C300
Engine Mount Replacement, Exhaust Issue, CEL
I have a 2011 c300 which has been running fine but lots of vibrations and rattles at stop from motor mounts.
I had a shop replace the mounts for around $1k, they mention that the exhaust had to be removed in the process and it needed some work from rust, some clamps/gaskets. Great, no problem.
I get the car back and the exhaust sounds much louder, especially at slow speeds. Almost a droning noise that lasts so long as the accelerator is pressed.
I then roll down a hill to a red light and the car starts shuddering with CEL flashing (misfire?) which goes away and hasn't come back.
Before this motor mounts replacement the exhaust and engine were mechanically fine, no noises or lights for over 18 months.
What went wrong here? Car is back at the shop now.
I had a shop replace the mounts for around $1k, they mention that the exhaust had to be removed in the process and it needed some work from rust, some clamps/gaskets. Great, no problem.
I get the car back and the exhaust sounds much louder, especially at slow speeds. Almost a droning noise that lasts so long as the accelerator is pressed.
I then roll down a hill to a red light and the car starts shuddering with CEL flashing (misfire?) which goes away and hasn't come back.
Before this motor mounts replacement the exhaust and engine were mechanically fine, no noises or lights for over 18 months.
What went wrong here? Car is back at the shop now.
Super Member
Joined: Apr 2008
Posts: 766
Likes: 173
From: Walnut Creek, CA
325Ci, 325Cic, C300
What went wrong may be the shop of choice. Who did the work? RWD? Then the exhaust did not need to come off. And if they did that, who knows what else they borked.
If you really want the internet to diagnose this, then read the codes, post it here, and maybe pictures of the general exhaust area from the bottom would help a lot.
If you really want the internet to diagnose this, then read the codes, post it here, and maybe pictures of the general exhaust area from the bottom would help a lot.
MBWorld Fanatic!
Joined: Sep 2013
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2021 GLB250 FWD, 2023 GLA250 FWD, 2013 C250, 2015 GLK350, 2005 ML350SE, 2003 E320
I have a 2011 c300 which has been running fine but lots of vibrations and rattles at stop from motor mounts.
I had a shop replace the mounts for around $1k, they mention that the exhaust had to be removed in the process and it needed some work from rust, some clamps/gaskets. Great, no problem.
I get the car back and the exhaust sounds much louder, especially at slow speeds. Almost a droning noise that lasts so long as the accelerator is pressed.
I then roll down a hill to a red light and the car starts shuddering with CEL flashing (misfire?) which goes away and hasn't come back.
Before this motor mounts replacement the exhaust and engine were mechanically fine, no noises or lights for over 18 months.
What went wrong here? Car is back at the shop now.
I had a shop replace the mounts for around $1k, they mention that the exhaust had to be removed in the process and it needed some work from rust, some clamps/gaskets. Great, no problem.
I get the car back and the exhaust sounds much louder, especially at slow speeds. Almost a droning noise that lasts so long as the accelerator is pressed.
I then roll down a hill to a red light and the car starts shuddering with CEL flashing (misfire?) which goes away and hasn't come back.
Before this motor mounts replacement the exhaust and engine were mechanically fine, no noises or lights for over 18 months.
What went wrong here? Car is back at the shop now.
If the CEL came on there should be stored codes.
Thread Starter
Newbie
Joined: Apr 2024
Posts: 2
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2011 C300
I don't have a scan tool, probably should get one after this.
The car is 4Matic so I think (?) removing the exhaust may be necessary or at least make the job easier.
The shop said the current problem was an exhaust leak and they fixed it, car sounds better and drives well, no issues so far.
I am a little concerned that I was initially given the car to drive with more issues than it went in with - I was just trying to do preventative maintenance.
The exhaust may have been rusty but it was in fine working order afaik, quiet and I passed emissions 2 months ago. So idk what really went on to cause that whole situation.
From what I understand, if the exhaust leak is upstream of certain censors then it could cause the engine to operate under the incorrect conditions and potential misfire on deceleration or stop.
Hopefully it was just a minor oversight reconnecting the exhaust and everything is in working order now but I will be vigilant.
The car is 4Matic so I think (?) removing the exhaust may be necessary or at least make the job easier.
The shop said the current problem was an exhaust leak and they fixed it, car sounds better and drives well, no issues so far.
I am a little concerned that I was initially given the car to drive with more issues than it went in with - I was just trying to do preventative maintenance.
The exhaust may have been rusty but it was in fine working order afaik, quiet and I passed emissions 2 months ago. So idk what really went on to cause that whole situation.
From what I understand, if the exhaust leak is upstream of certain censors then it could cause the engine to operate under the incorrect conditions and potential misfire on deceleration or stop.
Hopefully it was just a minor oversight reconnecting the exhaust and everything is in working order now but I will be vigilant.
Joined: Nov 2016
Posts: 7,847
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From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
