Very strange smell. Stumped

[Waterloo]

(12-10-2022 )Grumpyjoewv Wrote:  Well, I replaced the boot and it definitely helped, but I’m still getting the smell. It only happens at night when it starts getting chilly outside and I’ve noticed now it’s worse while I’m sitting still. With the engine off, it gets worse and worse for about an hour and then it’s gone. I’m thinking it’s gotta be a gasket expanding and contracting.

I was working on my truck a few years ago, and had some of the exhaust off, front and back of the turbo. I found a connection that did not have a gasket, that silver one with the slight concave. I called the dealer parts dept and they insisted there is no such gasket, it is a Cummins part, 5 inch, silver fibery thing... I would start there, from the turbo back. I will see if I have the Cummins part number for that gasket. Odds are, if that truck of yours was in the shop and they touched the exhaust, those gaskets were never replaced. Here is the Cummins part number, 2866337. There are normally at least two, possibly three between the turbo and the first can.

I am currently fixing a bad delete on a truck right now, and found those gaskets missing. Also, in the elbows around the turbo, there are o-ring gaskets at the metal to metal connections. I replace mine every few years, as they do get brittle. I apply anti-seize, the silver stuff, to help hold them in place, and extend their life.

I would get under the cab too, any slip joint connections or flex pipe, and look for holes in the bottom of the cab, especially if you have an APU installed. It could be something as simple as a hole that was cut, not used, and not plugged. Or, one of the factory plugs was removed and never replaced. Look at the firewall too, where the bulk of the wiring enters the cab...

Right now, I would bet it is one of those 5 inch gaskets that has failed, or was never installed if any exhaust work was done.