W124 320 Coupe Exhaust smell in cabin

[Mercky]

Hi, New here! I have a 1994 W124 320 coupe sportline with low miles (40k). A noticable smell of half combusted petrol/exhaust enters cabin only when window or roof are open whilst moving, this happens for about 3 mins after start up then vanishes. Also when travelling at speed, say 70 to 80mph, especially after kickdown, a heavier smell enters cabin, more oily and a bit "eggy", again window or roof must be open. Do exhaust gases enter cabin even at speed due to aerodynamics?? No smells apparent with window and roof closed. Is the CAT suspect? car runs well otherwise with good mpg etc. All suggestions welcome!! Thanks.
Mercky.

 

[190]

cat

Catalyst converters do give of a smell of rotten eggs sometimes try putting in a catalyst cleaner and giving it a good run. hope this helps.

 

[Mercky]

cat

thanks for the advice but I think my garage already tried that to no avail. Incidentally the car did pass all it's emission tests in its recent mot.

 

[flyingtech55]

Hi Mercky

I had a car once which had a slight exhaust smell all the time which was stronger when the windows were open (no sunroof). However the car ran fine.

Eventually turned out to be either a hairline crack in or a distortion of the exhaust manifold. Whatever it was I eventually changed the manifold (old car so plenty of cheap bits in the scrap yard) and the gasket (which looked OK) and the smell disappeared. The engine was quieter afterwards as well but the sound of the exhaust blow wasn't noticeable before and it was only after the manifold change that it was apparent. It must have been a very small leak but the smell was noticeable. There was no emissions test in those days!

This might be a place to start your search.

Hoping this helps

 

[Mercky]

smell

thanks Gliderman, the interesting thing is that if you drive the car in 2nd at high revs of say 5000rpm to simulate high speed the smell is not apparent, it's only when the car is actually travelling fast that it enters the cabin, I can only guess this means that it's been forced in the window or roof due to airflow over the car. Someone mentioned to me that the aerodynamics of a car behave strangely at speed and exhaust can actually be blown back around and over the car, not sure I believe this but it's a theory. Anyway getting the whole exhaust checked carefully is certainly an option....cheers.

 

[Ade]

Hi Mercky and Gliderman

Interesting bit from Gliderman about the hairline crack in the exhaust manifold. I've noticed one in mine (230TE 124) about 20mm long by pot no. 3 which I believe is making an annoying ticking sound that, as Gliderman suggests, isn't something you'd immediately associate with the exhaust system. Haven't got the smells though which is suprising because of this combined with recent problems with my cat.

I didn't realise you can get cat cleaners, how do you administer them and where are they available from?

Ade

 

[Spike]

Another common place for exhaust fumes to enter the car is through the plastic vents on each side of the boot behind the carpet around the wheel arches.

The vents are like louveres and can get stuck open with crud from the road.

Opening a window at speed will cause low pressure in the cabin and can draw exhaust fumes in through these vents as one is vent is near exhaust outlet on the nearside.

Worth having a look and maybe even temporarily tape the vent up to see if this is where the fumes are getting in.

 

[Mercky]

exaust smell

thanks spike, I've always wondered about the pressure issue with the windows closed/open so it's interesting you mentioned it. I'll have a look for those vents, are they on 320 coupes aswell?

 

[Spike]

Re: exaust smell

thanks spike, I've always wondered about the pressure issue with the windows closed/open so it's interesting you mentioned it. I'll have a look for those vents, are they on 320 coupes aswell?

Yep, they sure are.... look under your rear bumper on each side behind the wheels. The vents are in the bodyshell hidden by the bumper.

 

[43622]

Hi fellas,

just a note on the vents...I recently changed the aerial on my 420se (1992) and spotted these vents which were full of mud, dust and 'fluff'. on finishing the areial job I gave them a good clean down, and a wipe over with Auto glym bumper care( basically a rubber conditioner) after which I noticed that the car tended to smell much fresher, and less of the 'outdoor smog'. I'm guessing that the vents werenot closing properly because of the dirt.

It's certainly worth having a look. I would suggest removing the side wall carpet in the boot where the small luggage 'well' is, you will clearly see the vents.

good luck !

 

[robert.saunders7]

My C220CDi has the same issue - quite a stink if driving, especially at higher speeds, with window open. Obviously, don't always drive with window open, seems pointless as the climate control is so good, but interesting all the same. I will check the vents too....

 

[190]

My C220CDi has the same issue - quite a stink if driving, especially at higher speeds, with window open. Obviously, don't always drive with window open, seems pointless as the climate control is so good, but interesting all the same. I will check the vents too....

Why not buy a 190 they don't smell (if you wern't possers driving with your windows down tou would not smell the smell.) I bet you it goes away in the winter when your windows are closed

 

[Mercky]

exhaust smell

Thanks Spike, you were absolutely right! I removed the trim in the boot well and found the vent on the nearside had actually fallen out! On replacement the problem had fairly definitely vanished, even double checked and removed it again and smell reappeared. Interesting to note the back side of the trim was all blackened. What are these vents actually for? Anyone know? Anyway thanks Spike and to everyone who left helpful replies!!!

 

[Spike]

Just goes to show that its often the silliest things that cause problems.

I do wonder how long it would have taken a MB garage to diagnose the problem. You can picture the scene... Sorry sir we cant seem to diagnose the fault. There are no errors coming up on the star readout. We could change the ECU to see if that will fix the problem only about £495 + 2 hours labour. :twisted:


As I understand it, the vents serve 2 purposes.

1. To stop/reduce dampness in the boot.
2. To make sure you dont get a vaccum lock in there if the bootlid was last shut in higher ambient tempreratures.



Still a potentially fatal design if it allows the cabin to fill up with carbon monoxide tho

 

[azmi]

wow,

thanks for the info. What happened if i closed the vet altogether ... i once thought that these wholes(vents?) are source of road noise and in my quest for better audio listening, i actually plugged the whole and covered those with dynamat!!

i now wonder if i should re'vent' the boot area.

As I understand it, the vents serve 2 purposes.

1. To stop/reduce dampness in the boot.
2. To make sure you dont get a vaccum lock in there if the bootlid was last shut in higher ambient tempreratures.