AC system drawing in exhaust

2015 High Miler · February 12, 2022

I’ve been having this issue for some time. Probably 80-100,000 miles. (I feel like it started after the dealer did a transmission replacement but can’t get anywhere with them.)

The short of it is when I stop at a light, I’m getting exhaust smell in the cabin through the AC. Doesn’t do it at all going down the highway but as soon as you get off and stop at a light or whatever, the smell starts. When I took It to the dealer, they said it was an exhaust gasket leaking and cracked manifold and needed to be replaced at $3400. F that BS.

I now have long tubes, stainless ORY pipe through an X to dual mufflers and tail pipes out the back. I started with the headers and Y pipe and progressed on back. None of this helped the smell.

I like this truck a lot and don’t really want to go buy an overpriced truck right now. I’d like to figure this out.

I'm fairly knowledgeable about mechanical stuff but I cannot fin where this is coming from or how to fix it. It really only does it after driving, then stopping at a light or stop sign.

I’ve posted about this before and did not get a lot of response but the site has grown and I am hoping someone has some ideas on what to check.

thanks in advance

shakenfake · February 14, 2022

On 2/11/2022 at 7:38 PM, 2015 High Miler said:

I now have long tubes, stainless ORY pipe through an X to dual mufflers and tail pipes out the back.

Well there you go just found your exhaust smell lol

2015 High Miler · February 14, 2022

14 minutes ago, shakenfake said:

Well there you go just found your exhaust smell lol

Thanks for the bump, but I guess you missed the part about it doing it prior to those changes and that is why I made the changes... It started after I had the trans replaced at the dealership. The dealer said it was exhaust gaskets and a cracked manifold. Neither was bad when I removed them. The dealer doesn't know what it is or "how it could happen" but I think they just dont know and are throwing guesses out. So I am trying to diagnose it myself.

It's Tim · February 14, 2022

If you know anyone that does HVAC see if you can borrow a combustible gas detector.

newdude · February 14, 2022

Exhaust smell in the cab from your truck = leak under the hood or near where the HVAC inlet is picking it up.

You should smoke test the exhaust system via the tailpipe and see if smoke starts pouring out somewhere.

shakenfake · February 14, 2022

Ah I misunderstood the dealer portion. I thought you took it to the dealer once for the transmission as well as for the exhaust leak at the same time. Didn't know that was two different issues.

2015 High Miler · February 14, 2022

2 hours ago, shakenfake said:

Ah I misunderstood the dealer portion. I thought you took it to the dealer once for the transmission as well as for the exhaust leak at the same time. Didn't know that was two different issues.

yeah, it was initially taken in for the trans replacement, then it was getting exhaust gasses in the cabin after that and they said that the exhaust manifold "donut" had come loose. They fixed that and then about 20,000 miles later, it started again and that's when they said it was a cracked manifold, bad gasket etc. $3500 fix. From there, I put on the headers, y pipe and exhaust. Still smells in the cabin when stopping.

IDK WHY I have not thought to smoke test it... will do that asap. Thanks!

2015 High Miler · February 18, 2022

I had the exhaust system smoke tested and no leaks were found. Back to square one.

I dont know how else the exhaust can get in to the AC system other than the air intake.

lolpops · October 1, 2022

Hi

lolpops · October 1, 2022

I've got the same problem ! Did you fix it ?

Thanks

2015 High Miler · October 4, 2022

no, it still does it at 237,000 miles.

movario · October 4, 2022

Have you tried to block the exhaust tip when idleing and have another person "hear" for leaks?

Edited October 4, 2022 by movario

2015 High Miler · October 5, 2022

I had mine smoke tested and there were no leaks found.

I have changed my whole exhaust system: long tube headers, ORY pipe w X pipe and dual exhaust out the back. No better and no worse.

Edited October 6, 2022 by 2015 High Miler

2015 High Miler · March 12, 2023

I bought a 20 19, 2500 HD last March. In October or so of last year, I started getting the occasional exhaust smell in my air conditioner as well. This truck has 74,000 miles and has zero modifications. It really is aggravating that no one can figure this out. I can’t imagine that I’m alone and have the only two trucks that have this problem.