Exhaust smell in cabin: Looking for ideas

[JustPlaneChris]

Hey guys!

I've got a weird issue, hoping the brain trust here can give me some ideas to pursue.

I get an exhaust smell in the cabin when I run up through the gears to ~ 80 mph, say merging onto the tollway.

The first time it happened I thought it was someone in front of me going "open loop" getting on the highway, but then it happened when I was alone on the road. Things I've noticed:

• It isn't super strong smell, and it doesn't last long
• Doesn't have to be full throttle (but it usually is LOL)
• Can't smell it if the AC is on recirculate
• Smells "post cat" to me
• Can't hear any evidence of an exhaust leak when idling
• Dealer "could not replicate" (naturally)

Any ideas of things to check? I even wondered if it was speed-related, maybe somehow pulling air in from the rear of the car in the low pressure zone that's there at speed. But that would mean a very leaky trunk seal, or some sort of air intake at the rear (neither of which I think are likely).

[jimrobbington]

I never smell my own exhaust in this car. Kinda miss the test pipe smell of my oils A4. I would look at the flex pipe.

[JustPlaneChris]

Is the flex pipe visible without putting the car up on a lift? Unfortunately I have no way to get it off the ground myself.

EDIT: I found a drawing of the exhaust system over in the x-pipe thread that shows where the flex section(s) are located. I doubt I'll be able to see much from above or below, but I'll get a light and see if I notice anything obvious.

[mr shickadance]

a <2 year old car should not be having exhaust leaks due to rust, so my next line of thought would be if you banged the exhaust on something in the road at some point? or during the install of your brace?

could you describe the smell? is it a sulfur, almost farty type smell? if yes that's your cat, and it's normal if it's not warmed up and you go WOT.

[JustPlaneChris]

I got the car used, so no telling what happened in its first life, but since I've owned it there hasn't been any incidents. The CR-15 brace is just a strut tower brace, so that's nowhere near the exhaust.
The smell is not the same as "cold car exhaust smell", and this happens well after the car is at normal temps. To my nose it just smells like when a car ahead of you puts foot to the floor and goes "open loop". You know, just slightly rich but still cat-treated exhaust.

I've been searching the forums more, and some have had cracked flex pipes from bad motor mounts. Mine was just in for 25k service, you'd think they might have noticed something like that if it were the cause.

[JustPlaneChris]

Well, I'm still getting this smell in the cabin after spirited driving - unless the AC is on recirculate. I called the dealership again and they want me to bring it in and take the shop foreman for a drive and duplicate it. That means (to be safe, I guess) I'll be pulling my intake tube off the car and returning it to stock configuration before going in. That's a PITA, but call me paranoid.

I did shoot a couple of photos from underneath of the flex pipes, but I don't know what they are supposed to look like. <shrug>

[BABurgman]

The flex pipes look good from that angle. They will need to look at the manifolds, the flex pipes and where they connect to the manifolds to see if there are any leaks.

[JustPlaneChris]

Thanks Brian! I will be sure they do, when I take it in.

I've decided I'm not going to put my stock intake hose and filter back in, since I have documented evidence it had this issue when it was all stock and they cannot logically blame an exhaust leak on an aftermarket intake hose. Yes, I'm lazy.

[chet.rowles]

My guess is it's just a bit of oil burn off when mashing it.

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[JustPlaneChris]

My guess is it's just a bit of oil burn off when mashing it.

Hey, another Austinite!

Now that you mention it, maybe it does have a slight oil-ish aroma....
But burn off from what? Where? And how would it be entering the cabin air intake?

[BDP]

I've got the same thing going on but I have an AWE exhaust. Seems like over time (2 months) it's moved around and shook something loose and I have a leak somewhere. I need to get it up on a lift and start to tighten things up.

The stock exhaust liked mentioned above leaks a lot at the clamps that connect the downpipes to the exhaust...mine did.

[JustPlaneChris]

The stock exhaust liked mentioned above leaks a lot at the clamps that connect the downpipes to the exhaust...mine did.

Do you mean at the top where they connect to the manifolds, or at the bottom beyond the baby resonators where it connects up to the rest of the system? Because if it's the latter, I'll just go ahead and take it in to the exhaust shop and have those babies cut off and a Magnaflow X-Pipe welded in.

[BDP]

Do you mean at the top where they connect to the manifolds, or at the bottom beyond the baby resonators where it connects up to the rest of the system? Because if it's the latter, I'll just go ahead and take it in to the exhaust shop and have those babies cut off and a Magnaflow X-Pipe welded in.

It's this piece here that leaks...

https://www.ecstuning.com/Audi-B8_S4...aust/ES315746/

You will have two of them, one for mating the end of the downpipes to the rest of the cat back. Mine had visible black exhaust marks from the leak and you could smell exhaust on hard accelration. Now I have the same smell probably the same issue elsewhere on my AWE exhaust. Hope this helps.

[JustPlaneChris]

Yes, that does help! I will see if I can stick my phone up under the car and get photos of those clamps. Thanks!

[chet.rowles]

Low pressure behind the car if your hvac is on in any capacity

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[JustPlaneChris]

Low pressure behind the car if your hvac is on in any capacity

That was one of my early theories too, especially since it seems stronger when you acellerate to speeds-one-should-only-do-on-Texas-130, if you know what I mean.

I discounted that theory when I could find no path for incoming air to get inside the car from the aft end. Unless I've missed something obvious!

[chet.rowles]

YES, good old 130. The Area at the front of the windshield is also a low pressure area, IIRC, which is where hvac would draw from. I wouldn't worry about this.

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[JustPlaneChris]

Looks like I may have some leakage around one of the clamps? Either way, they are going away as soon as I do the x-pipe mod. Beyond that, I'm not going to fixate any more. It's not a strong smell, and there are no obvious leaks that are going to kill me with CO.

[JustPlaneChris]

Update: Because we are going to be doing some road-tripping this fall, I wanted to get eyes on the exhaust system. Took it to the dealer this morning, they gave it the once-over and found nothing leaking, no obvious problems. Took the service manager for a drive and of course I couldn't get the smell in the car. Dammit! On the way back to work, I gave it a blast (with windows down, this time) and got the odor. <sigh>

They did notice that both cats appear to have been replaced (the paper p/n sticker was still on them), and also the dealer I bought the car from had hosed down the engine with that shiny detail spray crap. They think perhaps I'm just getting smells from those items, but that makes no sense because it would be constant and not just when I'm wailing on it. I dunno what to think now.

[14S4GWM]

I had a similar issue with my WRX, could only smell it with the windows down. Turned out it was my trunk seal. The vacuum that was created with the windows down pulled the exhaust into the car. Might give it a look.

[JustPlaneChris]

I pondered that as well, since I know there's a low pressure area back there. I'll give it a good look, thanks!

[PSUGOLD]

I have it in my with the Borla. I am getting new front pipes next week under warranty as they were leaking from the flex joint from one of the photo posted above. I also have carbon buildup around the clamps as you can see from these photos, going to bring it in next week to replace the front pipes that were leaking and also readjusting the other connectors. I also wonder if the noise I hear when I turn hard left is air shuddering from the exhaust leak. I was also told these black marks from small leaks are common with systems that are not welded together as the gas will escape a little from the clamps at times.

[JustPlaneChris]

The service manager told me the black stains on mine (which are MUCH less than yours) were actually water stains, from the moisture that condenses in the system when it starts to warm up, and it then seeps out before everything heats up and expands to seal tight. I guess that's a reasonable explanation, but it still doesn't give me a lot of confidence in having a leak-free system over time. No mention was made of any leaks from my flex joint(s) when they had the car on the lift.

I will have the muffler shop give it a close look when I take it in for the "X-pipe mod" in a couple of months.

[PSUGOLD]

Mine MAY be water related too somehow. I remember about a month ago driving through a massive storm and thinking my exhaust was going to fall off. I kept hearing noises from under there when I went through puddles, so maybe the water + the heat + some small leaks led to that. The mechanic looked at it last week for me though and cleaned off the flex pipes, soaped them up, revved the engine and saw the soap bubbles coming from that area showing the leak. Should have them by next week to get installed and then HOPEFULLY it will fix the damn noises when I turn left too.

The service manager told me the black stains on mine (which are MUCH less than yours) were actually water stains, from the moisture that condenses in the system when it starts to warm up, and it then seeps out before everything heats up and expands to seal tight. I guess that's a reasonable explanation, but it still doesn't give me a lot of confidence in having a leak-free system over time. No mention was made of any leaks from my flex joint(s) when they had the car on the lift.

I will have the muffler shop give it a close look when I take it in for the "X-pipe mod" in a couple of months.

[MagnaFlow]

cleaned off the flex pipes, soaped them up, revved the engine and saw the soap bubbles coming from that area showing the leak.

We'd recommend giving this a shot, too. Its an oldschool method but works well! Any exhaust shop should be able to do the same thing if you arent able to get under the car for any reason.

[JustPlaneChris]

We'd recommend giving this a shot, too. Its an oldschool method but works well! Any exhaust shop should be able to do the same thing if you arent able to get under the car for any reason.

Thanks! If it is the flex pipes leaking, I want to get that fixed under warranty before I have one of your products welded in at the local muffler shop.

[juniorcruzer]

Anyone been able to get to root cause on this yet? I noticed the smell something terrible after going through a car wash the other day.

Jon

[Sivill]

Maybe one day we will find rhe issue. My 6 year old complained of this issue in my car. I noticed it was on start up only. Past week it's become super bad. Looking for ideas. I hace 8.5k miles and i am wondering if it's vacuum/ Intake related

[SwankPeRFection]

This is usually an issue with the flex joints in the downpipes breaking down. You don’t see it unless you take them off and then you’ll see they twist too much and generally are worn down and rusted from the inside out and breaking apart.

[BrokeBichB8]

I got one of those carbon air filters from china for "pollution" and it made a drastic difference in my opinion. 8KD819439.

No root cause but a help.