Exhaust smell after going downhill

barge1914

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Pegaso, Euro 6C1, auto, 17000 miles. Age 2.5 years.



I have occasionally in the past noticed a smell of exhaust after long downhills.

Today after coming down Stelvio Pass it was particularly noticeable when we stopped at the bottom.

But oddly no smell after the long hard climb up.

The smell is that of ordinary diesel exhaust fumes not the usual polite whiff of a Euro 6 with cat and adblue. Smelly but enough inside to get the CO alarm excited.

No noticeable extra noise from exhaust or engine.

No noticeable change in performance or other signs of anything wrong.

Not sure what it could be.

Is it perhaps some phenomenon whereby insufficient adblue gets injected during engine braking?

Any ideas?

Any idea whether exhaust issues are covered under third year warranty bought through Fiat dealer?
 
This probably won't be much help but my ancient 1996 2.5td Kontiki has done this for as long as I can remember. 14 years I have had it. Worse than that at the bottom of a huge pass like the Tourmalet when you finally give it some throttle the backed up smoke is like the funnel of a battleship at full chat. Looks horrendous but it drives fine. Five minutes later it's clear and fine. Nobody has ever been able to explain it to me.
 
barge1914 said:
Today after coming down Stelvio Pass it was particularly noticeable when we stopped at the bottom.
But oddly no smell after the long hard climb up Any ideas?
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I,d out of choice never stop after a long descent better to drive for a way to clear the engine/exhaust and give the brakes a chance to cool. I,ve seen brake discs glowing at the bottom of descents when people stop to let them cool
 
www.feoa.net

Smoking out tailpipe after going down hill

My daily commute takes my trough the mountains and after coasting down the mountain for about 5 miles my cars smokes very bad once I hit the gas again. It's a large and embarrassing plume of smoke out the tailpipe that continues until I reach cruising speed of about 65 mph. I smell oil when it...
www.feoa.net www.feoa.net
 
Fisherman said:
www.feoa.net

Smoking out tailpipe after going down hill

My daily commute takes my trough the mountains and after coasting down the mountain for about 5 miles my cars smokes very bad once I hit the gas again. It's a large and embarrassing plume of smoke out the tailpipe that continues until I reach cruising speed of about 65 mph. I smell oil when it...
www.feoa.net www.feoa.net
Click to expand...
No obvious smoke, but maybe because it’s synthetic oil. However engine is fairly new, so wouldn’t expect much ring or piston wear. Certainly it doesn’t normally use much oil. However with prolonged engine braking the high vacuum created in the cylinders could maybe suck more through comparative to the small amount of combustion fuel being used.
 
There should be no vacuum on a diesel with an open air intake, sounds more like a leaky injector on the common rail, or if some oil is vanishing it may be a worn or leaky valve stem seal, maybe not worth bothering about if it passes the ex test on mot.
 
Strangely enough after the following couple of days after the Foscagno, Livigno and Bernina Passes the whiff has gone away, perhaps it was just burning accumulated crud out of the exhaust system?
 
barge1914 said:
Strangely enough after the following couple of days after the Foscagno, Livigno and Bernina Passes the whiff has gone away, perhaps it was just burning accumulated crud out of the exhaust system?
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Normally a hard fast run does this not going downhill. 🤔
 
Spent some time in Fiat Professional garage in Domodossola today. Very willing and helpful, but try as they might they could find no problems with combustion or exhaust gasses. However they came up with one point of interest. The exhaust pipe is as standard for a Fiat panel van chassis. The A-Class body however is a fair bit wider with the result exhaust gasses instead of being disharged clear of the side, are discharged under the van some 250mm or more back from the perimeter so that when stationary exhaust can in the absence of air movement hover around beneath the van in all those additional side cavities, and find it’s way inside.

Why it happens mostly after long mountain pass descents and not ascents however is still subject to debate. Perhaps something to do with accumulation of crap from incomplete combustion with engine braking?

Has anyone else had a similar issue with an A-class, and more specifically a Roller Team Pegaso? Do other A-Class models have extended exhaust discharge pipes to avoid the problem.
 
barge1914 said:
Spent some time in Fiat Professional garage in Domodossola today. Very willing and helpful, but try as they might they could find no problems with combustion or exhaust gasses. However they came up with one point of interest. The exhaust pipe is as standard for a Fiat panel van chassis. The A-Class body however is a fair bit wider with the result exhaust gasses instead of being disharged clear of the side, are discharged under the van some 250mm or more back from the perimeter so that when stationary exhaust can in the absence of air movement hover around beneath the van in all those additional side cavities, and find it’s way inside.

Why it happens mostly after long mountain pass descents and not ascents however is still subject to debate. Perhaps something to do with accumulation of crap from incomplete combustion with engine braking?

Has anyone else had a similar issue with an A-class, and more specifically a Roller Team Pegaso? Do other A-Class models have extended exhaust discharge pipes to avoid the problem.
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There is no fuel being squirted in with the throttle closed, so nout to combust.
 
Whilst descending the air pressure outside the vehicle is greater than inside so whilst equalising exhaust gases discharged below the vehicle may enter the vehicle. Opening a cab window might prevent this occurring.

Whilst ascending the converse is true with pressure inside greater than outside so the problem will not occur.
 
Canalsman said:
Whilst descending the air pressure outside the vehicle is greater than inside so whilst equalising exhaust gases discharged below the vehicle may enter the vehicle. Opening a cab window might prevent this occurring.

Whilst ascending the converse is true with pressure inside greater than outside so the problem will not occur.
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Above 12000 ft and down maybe, unless he has gone supersonic LOL.
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Put a exhaust tip on which clears the van sill. Had flexible exhaust to attach to land rover when sited to clear fumes when vehicle was running to charge batteries.
If it's not being forced away from your van, it could eddy into pockets and seep into cab.
 
argoose said:
Put a exhaust tip on which clears the van sill. Had flexible exhaust to attach to land rover when sited to clear fumes when vehicle was running to charge batteries.
If it's not being forced away from your van, it could eddy into pockets and seep into cab.
Click to expand...
That's what I did with my Exsis, exhaust is on the same side as fridge vents. Does help, as did using winter fridge vents (when appropriate) and resealing around the fridge
 
Canalsman said:
Whilst descending the air pressure outside the vehicle is greater than inside so whilst equalising exhaust gases discharged below the vehicle may enter the vehicle.
Click to expand...
Good Point reminds me of the Pop when trying to open the toilet cassette on our first Col always leave it slighty cracked open now when driving mountain Cols
 
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