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Discussion Starter #1
Hey everyone!

I am more interested in ideas how to stop the smell from getting into the car and I wonder more if it is an aerodynamic or an interior/exterior pressure difference type of effect - and can this be stopped? Fast forward: My ideas to stop this nuisance are extending the muffler tip and/or sealing up the trunk area or rear part of the car somehow. Maybe even replacing weather seals? Or lining some of the gaps with a silicon or resin?

I will start by saying I have read the handful of other threads about getting exhaust smell in the car and I can summarize those conclusions quickly...

PREFACE:There is a "common" smell produced that is much like rotten eggs and people have established it is because:

(1)Stock catalytic converters going bad (replace cats)
(2)high(er) sulfur content in the fuel (low quality or particular brand of gas)

and usually happens when running WOT and/or car hasn't fully warmed up.

OKI can agree with this summary because I was experiencing this same problem with my stock exhaust manifold (very rotten egg smell, and getting worse) and recently when I switched to dezod green headers the smell changed to more of a "burnt hairspray" type of smell - most likely due to different/newer cats that come with the headers. This hairspray smell was worse at first but the more I drive the car it is going away (now just exhaust smell) -- BUT -- the WHEN of the smell still occurs under the same conditions (higher speeds at WOT). And Yes I properly broke in the cats EXACTLY per DEZOD instructions.

What I want to know is WHY does the smell even make it into the cabin? So let me be more specific...

I don't get the smell when the windows are up and the moon roof is closed. But if the moon roof is lifted/tilted or opened I immediately get the smell and it's 10x more noticeable in the back seat than anywhere (even with windows up). Roll the front windows down and it's a little better, roll just the back windows down and it gets much worse. Again... it's more common at higher speeds and heavier on the gas.

The reason I wonder if it is aerodynamic/pressure because how quickly it gets into the cabin when just the moon roof is cracked. Much like an airplane wing, I suspect we have high pressure under the car and lower above the car and pressure moves from high to low. With the amount of airflow past the car at 70-80 mph one would think the exhaust would be blown away by the passing air (unless it was a leak under the car), but it seems like it could be a "back draft" or counter flow driven by delta Pressure, enhanced by removing the restriction to the flow (cracking moon roof). Plus it gets into the back seat first, thus it's traveling inward from the most likely source (exhaust tip).

I have considered leaks but I have found NONE in my system. Plus I have no reason to suspect an improper install of the new headers - Vband sealed portions line up perfect, no gaps, and the gasket at the front of the BPipe is new and lined up well. No strange sounds coming from the exhaust. If it was a leak, where would be the most likely source?

Sorry for the novel, but I refuse to settle for "this just happens" without considering a few ways to keep this from happening. I may not be able to stop my car from running pig rich and making the smell for now, I CAN accept that..... but while I feel sorry for the guy behind me who smells my exhaust, I would like it better if it was his problem and not mine :lol:
 

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It is probably the rear cat... Check for any holes in the exhaust system.
 

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^^Op already said he checked for leaks. There are numerous body plugs under the car from front to back, I wonder if you're missing any. Another thing you can check if there is no exhaust leak is your fuel trims to see if you are running a bit rich. A defective/lazy oxygen sensor, a leaking fuel injector, or even a defective pressure regulator can cause a rich condition and basically flood the cats will unburned fuel. Even a bad coolant sensor can trick the ECM into sending too much fuel as it is a primary sensor. The rotten egg smell can be common during open loop when the car is running very rich but should fade once the car warms up. So it might be a good idea to see how your engine is running. Just a thought...
 

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PREFACE:There is a "common" smell produced that is much like rotten eggs and people have established it is because:
It's normal for cats to smell when they run rich, like they do when you're WOT. Typically when you're WOT, the 02 sensors aren't used. Instead, it uses the MAF to measure air and an open loop table in the ECU. If you watch your scanner when you're WOT, you can see that the ECU goes into open loop mode. One reason is that our narrow band 02 sensors don't react fast enough. It might be interesting to see what your mixture is WOT. Maybe the headers are so much more efficient, you're throwing the stock tune off.

Is everything else stock? You haven't change the injectors have you?

If you're not smelling exhaust with the windows closed I'd say it's normalish. Is your muffler sticking far enough out behind the bumper? I wonder if when you were messing with the exhaust, you managed to pull the muffler farther under the car.
 

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I had a similar problem a couple years ago. The rear quarter air vent behind the bumber has a flap door that had fallen off mine. I taped it off until the one I ordered came in, solved my issue 100%. They are kind of a PITA to get too, but worth checking.


 

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Savage_, ever firgure this out? I have the exact same issue w/exhaust (gas) smell w/windows down &/or moonroof tilt/open. The moonroof throws me for a loop too. It IMMEDIATELY comes in the car as soon as I open it. The smell literally completely fills the car on instant opening/tilting of the moonroof.

And you're right, the majority of the smell occurs in the rear of the car (backseat). Because letting the front windows down afterwards to get the smell out takes 30 seconds or so maybe. But if you put the rear windows down with or w/o the fronts down, the smell IMMEDIATELY leaves the car.

I plan on replacing all 4 O2 sensors when I order my Dezod headers. I hope that helps.

Q: You ever figure it out or get rid of the smell?
 

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Discussion Starter #8 (Edited)
I never completely solved this and the problem still occurs but it's not as bad.

I put the car on a lift and went to re-check the exhaust and found one of my v-band connections not quite tight enough. There was a bit of soot on the flanges at that connection that I didn't see on any of the others. So I have to retract my original statement: I did check for leaks and didn't find any but I probably had a small one (sorry dudes).

At the same time, I double checked my install to make sure I didn't re-position the muffler. No other configuration allowed the connections to seat properly so I assume it is correct. I would say the tip is more flush with the rear bumper than it is poking out past it.

This work helped but didn't solve. I had the car on a dyno recently and my open loop AFR was pretty rich (~11:1) so it makes sense there would be more odor but how it creeps into the cabin still puzzles me.

My best guesses would still be:
leaks in the remaining stock exhaust components
Missing underbody panels messing with airflow into/around the car (the large one beneath my motor ripped off during a polite and gentle road trip :rolleyes:)
muffler tip (EKB918 suggested)
rear quarter vets (JSB8096 suggested - probably a really good one to check but I admit I never made the time to do it).

As Jason said, there are reasons WHY it would make the rotten egg smell. I am running rich but I have done the 90K service, replaced o2 sensors and thermostat. The dyno shop also suggested fuel pressure regulator or fuel injectors as a cause.

Once I find a new job I want to get a whole new exhaust from the end of the dezod's back and have the shop ensure the muffler tip pokes out a little. And another underbody panel. Then try to figure out why I'm running rich. I do think these are 2 separate problems. One causing the odor and the other letting it into the car. Just because the exhaust smells better or worse doesn't mean it's "OK" for it to be in the cabin.

Will do my best to get back on and update my findings. If you want to help get results faster you can help me find a job :grin:
 

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A "rotten egg" odor would point me in the direction of burning oil. i.e.: sulphur. It could still be indicative of burning fuel though.

I can smell a farm or landfill when I drive by with all windows up and recirculation vent closed... in multiple vehicles and various times of year. Smelling your own car inside the cabin doesn't mean anything. Pinpointing the cause of the smell is what's important.
 

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Discussion Starter #11
^ I agree it's important to address the cause for best performance and reliability. This is the first car I've driven that I've ever encountered this problem though.

Also, blkdout, I've been following your build and it looks amazing so far. Just let me know if you want to swap cars for a month and take on my car as a project! lol
 

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^ I agree it's important to address the cause for best performance and reliability. This is the first car I've driven that I've ever encountered this problem though.

Also, blkdout, I've been following your build and it looks amazing so far. Just let me know if you want to swap cars for a month and take on my car as a project! lol
High mileage vehicles will definitely do that.

haha, my car still has so much to be done. Maybe you can finish it for me.
After the initial turbo install, it just wreaked like gasoline inside and out no matter how or where I was driving :lol:
 

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Discussion Starter #13
If by finish it you mean take it to the tuner and then drive it, NO PROBLEM!!

Hopefully some exhaust work and body fixes will stop the smell. I know a landfill or papermill will stink no matter what but I feel that exhaust stink should disappear into fresh mountain air when you're going 70mph, not back into the car. My 95 Accord is at ~150k miles and smelled terrible when the cats went out but it didn't come in the car the way the Lex does.

I may have to consult the project civilize thread for some creative ideas.
 

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I never completely solved this and the problem still occurs but it's not as bad.

I put the car on a lift and went to re-check the exhaust and found one of my v-band connections not quite tight enough. There was a bit of soot on the flanges at that connection that I didn't see on any of the others. So I have to retract my original statement: I did check for leaks and didn't find any but I probably had a small one (sorry dudes).

At the same time, I double checked my install to make sure I didn't re-position the muffler. No other configuration allowed the connections to seat properly so I assume it is correct. I would say the tip is more flush with the rear bumper than it is poking out past it.

This work helped but didn't solve. I had the car on a dyno recently and my open loop AFR was pretty rich (~11:1) so it makes sense there would be more odor but how it creeps into the cabin still puzzles me.

My best guesses would still be:
leaks in the remaining stock exhaust components
Missing underbody panels messing with airflow into/around the car (the large one beneath my motor ripped off during a polite and gentle road trip :rolleyes:)
muffler tip (EKB918 suggested)
rear quarter vets (JSB8096 suggested - probably a really good one to check but I admit I never made the time to do it).

As Jason said, there are reasons WHY it would make the rotten egg smell. I am running rich but I have done the 90K service, replaced o2 sensors and thermostat. The dyno shop also suggested fuel pressure regulator or fuel injectors as a cause.

Once I find a new job I want to get a whole new exhaust from the end of the dezod's back and have the shop ensure the muffler tip pokes out a little. And another underbody panel. Then try to figure out why I'm running rich. I do think these are 2 separate problems. One causing the odor and the other letting it into the car. Just because the exhaust smells better or worse doesn't mean it's "OK" for it to be in the cabin.

Will do my best to get back on and update my findings. If you want to help get results faster you can help me find a job 😁
 

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I have an is and they just did a recall on the low pressure fuel pump which in turn can stop the cats from working properly and not convert the gasses proper which in turn can push the sulphur smell up into your cab. This stated going on around 3 years ago with my car when I became sick. I have seen specialist and drs no one can tell me what’s going on with me and every symptom I have points directly at sulphur dioxide poisoning.
 

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I have an is and they just did a recall on the low pressure fuel pump which in turn can stop the cats from working properly and not convert the gasses proper which in turn can push the sulphur smell up into your cab. This stated going on around 3 years ago with my car when I became sick. I have seen specialist and drs no one can tell me what’s going on with me and every symptom I have points directly at sulphur dioxide poisoning.
First generations do not have issues like that. You are talking about a later model. Try talking in the right year section. Tose members may be able to be helped with that info.
 
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