Intermittent bad exhaust smell in cab?

[summit151]

Hey everyone so my friend has a 2018 GMC Yukon that only has 30000km on it and since August she has been getting a intermittent very bad exhaust smell in the cab. She has taking it to severely dealerships and they can not find the problem. It only happens once in awhile while driving it. I recently took it for a drive with my personal gas monitor that reads CO and it it started to read a very large amount of CO when I was test driving it and I could smell it very easily. I the took it back to one of the dealers and took a tech for a drive with the monitor and of course it didn’t get any smells on the cab. I tried to change the setting with the heater controls and recirculating air control and it didn’t help. She now has called me again saying it was very bad on the way to work again. The dealerships said they have gone through everything possible? I mentioned maybe a manifold leak but the said it would be noisy if that was the case. I am wondering what could have been missed that I can look at? And what is the best step going forward? 

[Colossus]

 Wow... This is a head scratcher. 

[silveradosid]

is the smell like rotten eggs or propane

[summit151]

It certainly is a head scratcher. Driving me crazy. She said it smells kinda like rotten eggs. I just smelled a exhaust smell when I got it to act up

[jagabom (Esquire)]

My car had an exhaust leak that I could only smell when stopped.  When driving the air coming through the rad would push the exhaust down the firewall and out so no smell.  Exhaust when stopped would come up the firewall and seep into the intake vent for the heater.  No smell on recirculate but this is a 2007 so recirculate shuts off outside air completely.  Was somewhere by the manifold close to the engine as I could feel hot exhaust if I put my hand down there during a cool day.  Not any nosier though.  This was a 2.4 L 4 cylinder.  Sold the car.  In the old days we would put a potato up the exhaust and if the vehicle stalled then exhaust was sealed.  It is funnier if you just put the potato up there and leave and start the car and rev it up.  Just like a rocket blowing it out. 

Jim

 

Edited December 8, 2020 by jagabom (Esquire)

[garagerog]

Possibly the flex connection after the exhaust banks Y?  Not sure on a Yukon, but typically that would be under the firewall, cab area and would make sense if it's being smelt in the cabin. The rotten egg smell was typical of catylitic

converters of the mid-70's before they were located closer to the exhaust manifolds where they heat up and do their job quicker and more efficiently now.

[Arcterrax]

I have the same thing right now. It smells like exhaust/unburned off gas. Worse when stopped at idle with the cold it being really cold. 2014 Chevy Silverado. Did you figure out the problem?

Edited January 27, 2022 by Arcterrax

[Apexwagon]

On 1/27/2022 at 6:03 AM, Arcterrax said:

I have the same thing right now. It smells like exhaust/unburned off gas. Worse when stopped at idle with the cold it being really cold. 2014 Chevy Silverado. Did you figure out the problem?

I have the same issue in my 14 Silverado, has anyone found the cause to this? Mine started after a transmission fluid change where i needed to get the exhaust out of the way of the pan using a tie down strap and 2x4 so I'm guessing its in the flex pipe or i destroyed a gasket somewhere. Looked everywhere cold and hot, thought it might even be the oil catch can leaking but it's sealed. 

[2015 High Miler]

Have had the same issue in my 2015 and have yet to find the cause.  Mine started after the first trans replacement (122,000).  Had it tested and found no leaks. Only does it when stopped.  As long as I’m rolling it’s not there.