Engine Sounds Rough Under Load

[mbenz76]

Noticed this for first time today. Accelerating up a "very" steep hill to 30mph and engine sounds really rough. On flat or revving when idling and engine sounds fine. Did a few laps to check and it is every time engine is put under load.

It is a strange noise to describe. It isn't just a loud version of the usual "drone" of a running engine. It's almost you can hear each individual "fire", and the harder the load the louder the noise, the faster the car the faster the noise.

Tried gearbox in Comfort (which is what it was in when I noticed it), Sport, and Manual. Noise is the same in all.

Had no issues like this with car to date.

Wound windows down and tried and could not really hear it from outside. Could hear a whine though which I suspect is the turbo?

Any ideas what it might be?

I have owned the car from new and have done relatively low mileage until recently. Put about 18k on in the last 18 months and have about 1k to do next week. Car is due A service in February.

Car is under a Tier 1 warranty from MB so hoping any issues are covered under warranty.

Thanks in advance.

 

[stwat]

Blowing exhaust downpipe maybe.

 

[mbenz76]

Blowing exhaust downpipe maybe.

Never thought of that.

Car was only in for new tyres about a month ago and they did a video of underneath it while narrating for me what condition various things were in and never mentioned the exhaust as being on it's way out. In fact I remember thinking it looked in good condition.

Annoyingly an exhaust wouldn't be covered under the Tier 1 warranty I don't think. Suspect it is wear and tear.

I'll have a look at what I can see from above in the daylight tomorrow.

Going to book in with MB I think to get it looked at as I have a lot of miles to do over next 2-3 months.

Any other suggestions most welcome.

 

[mbenz76]

Not sure it is exhaust. Can't really see it due to how well everything is hidden away in the engine bay, but having driven along a quiet road with a wall on one side I pushed it harder to get the noise and it just doesn't sound like exhaust.

I have replicated on the flat by accelerating hard, but it is "much" more evident on hills, and the steeper the hill the louder and more pronounced the noise.

Also it wasn't really noticeable this morning (despite me trying) until the engine warmed up.

It sounds like I have took my V6 diesel out and put a V8 petrol in! It is more "throaty". I actually wouldn't mind if it had always done this but it hasn't so something has clearly changed. When I asked my wife if she could her it, she described it as a helicopter sound - that swish swish swish swish noise - only "throaty". It sounds like I am hearing every turn of the engine.

Luckily the MB dealer in Sheffield I use for service is only 5 mins drive from the steepest hill for miles so I can take a tech out and show them what I mean at least when they get me booked in.

I'd still be happy to hear what others think.

 

[Reading1800]

Did you sort this, i have an odd droning noise when under pressure?

 

[Stratman]

Check for a blowing injector. Remove the engine cover then look and listen for a chuffing sound while the engine's running. while the cover's off take a look for carbon deposits in one or more injector wells.

 

[mbenz76]

Never got to the bottom of it, but it cleared up on it's own. I put it down to a bad batch of fuel making it run rough maybe.

Thankfully no repeat since.

Hope you get yours sorted. I know how annoying these things can be.