Exhaust in Cab on Mountain Descents

Drove into the Sierras last weekend and rediscovered an exhaust smell in the cab that only seems to show up on mountain descents. I pulled the cover expecting black death and all is well, the injectors are looking great too. Thankfully.
It seems to happen when the van decides to apply some engine braking going downhill.
Many Thanks,
Michael
2003 T1N 140 Wagon

Do you have any leaks in your cabin filter housing/cover (there is a foam seal). Any holes in your floor or firewall?

how are the weather seals on the rear doors? Is it possible that a tail wind was blowing exhaust through a gap in the rear rubber? I’m assuming that you popped the hood and checked for obvious exhaust leaks in the engine bay and checked the integrity of your exhaust underneath. If not pay close attention to the point where the down tube goes into the cat. The weld is known to rust out. Vic has a fix for this in his cheap tricks thread, if that’s the case

MPW said:

...
It seems to happen when the van decides to apply some engine braking going downhill.
Many Thanks,
Michael
2003 T1N 140 Wagon

Click to expand...

I'd check very closely for exhaust system leaks.

I've delayed some exhaust repairs at times. At those times I've noticed what you describe on downhill runs. My theory is that the catalytic converters load up a bit and create the smell. If the exhaust system is tight it isn't noticed.

As BrennWagon mentioned, the connections between the Flex pipe to Cats and Cats to muffler will rust out at the welds much before the other main parts deteriorate.

vic

Added:
Further reflection.
I still believe that the catalytic converters load up a bit. Another factor is the low flow through the exhaust system to concentrate the mixture during longer engine braking. The concentrated exhaust "seeps" out of the leaks into the turbulent outside air vs blowing out at pressure to be thrown further out.

Some leaks (like at the manifold) may only show up hot or under pressure. But the shop vac pressurization method works quite well.

The Sprinters (that have MB-built rear bodies) all have vents hidden in the lowest rear "quarter" (sixteenth?) panels.
They're there to create a partial vacuum to flush air through the van. They louvered, but i don't know if it's an active "seals when not moving" system.
They could be providing an in-road for gasses accumulating in the rear.

This is the T1N, the NCV3 is very similar:



--dick

The vents have a rubber flap which helps to prevent ingress. Whenever the vehicle is moving at speed, these pull air out of the body and interior. There are also drain holes along the bottom of the body.

The spare tire access bolts in the rear threshold are not sealed either, these can let dust and odor in at low speeds.

Thanks for the insight gentlemen. I'll give the Shopvac method a try and find that leak.

1.) Make sure your fresh air system is set at “fresh air” and that the motor to close or open the flap is working.
2.) Turn your fresh air FAN to HIGH, so it’s pushing fresh air through the vehicle, where it will exit at the vents.
3.) Make sure your windows are closed.
4.) Make sure the rubber seals on all your doors are tight.
5.) Get that exhaust system “tuned up.”
Confession:
I neglected my 2004 Sprinter Passenger Wagon’s exhaust system. 143,000 miles on original exhaust system. I had to make a SNAP lane change on the expressway, when a panel truck and I were both attempting to occupy the middle lane of three. THAT abrupt maneuver caused the exhaust system to SNAP IFF , just below the exhaust manifold. I saw the catalytic converter and muffler rolling across the highway to the shoulder.
By the time I exited, and drive around to that location, IT WAS GINE! Ha! Ha! But not funny ha ha. Tom