yungone501

iTrader: (4)

Ok, if you own one of the early model 2G MDX's, you've more than likely noticed the heavy scent of exhaust after or during acceleration. If you have kids, this can be especially dangerous not too mention just outright annoying! After reading post after post after post and seeing no slution I decided to take a gander for myself in determining what the problem was. So, on my ONLY day off (Sunday) I came up to the shop and began. I knew that the smell was coming in from somewhere that the exhaust was either leaking from or exiting from. Because I had previously conducted an exhaust leak smoke test I knew it had to of been the latter.

Finding the entry point was pretty easy, I went to the rear of the vehicle and dismantled the rear liftgate area (interior trim pieces) but found nothing that would suggest a ventilation duct. Then, after laying down on my back Rambo style and searching around right behind the rear bumper, I found the "cabin ventilation duct" maybe 1-1.5ft away from thedrivers exhaust tip....yes, it was that damn close.

Here in this first picture, Ive put a circle where the vent sits behind the rear bumper. You can actually see the vent by laying on your back and slightly peeling back the plastic fender well lining.



This picture shows the area of which must be reached in order to access the duct to block it off. You cannot block the duct from the underside as it is a one-way vent and has a flap that prevents anything from entering from the outside.



Here you can actually see the duct but in order to physically reach the duct, you must remove a module thats held in place with two 10mm nuts thats directly mounted below the rear fuse block showed in this picture. Again, the you can see the point of entry for the exhaust that Ive highlighted with the yellow circle.



and another from a little better angle of the duct...



Just to confirm this was my problem, I stuffed about five green microfiber (its what I had laying around, what?) rags inside the duct and then went for a ride to see if the smell had been eleminated. I also recommend temporarily doing the same before permanently capping it off. Btw, I used the expanding foam from Home Depot to give me my final result. Sorry, no pictureswere taken of that.



In summary, Im suspecting Acura thought (or didnt think at all) that the flapper would prevent this issue from occuring but failed to realize that wind gusts, vehicle movement, cabin pressure differences would all be factors in allowing the exhaust to enter the vehicle. This shoulve been a safety issue and atleast made a TSB so that all MDX owners would know how to fix the issue. I have 5 yes 5 kids and dont want them having tobreah in carbon monoxide while taking road trips or just while Dad decided to floor the motor every once in a while...you know? Anyhow, hope this helps anyone who has the issue.

dominik331

Interesting. Although I do have a 2007 X I have never noticed any scent of exhaust, unless it's coming from other vehicles driving near me.. Thanks for the info.

rcy

Maybe not a big deal in Texas, but in colder climates I wonder if blocking that would cause fogging in the vehicle during the winter.

Wonder if there is a vent on the other side as well?

larso1

Hmm, I'm wondering too what the unintended consequences might be by permanently capping off the only fresh air source, if it is indeed the only one. Here in CO it would definitely be a problem with moisture buildup in the cabin during winter. If there could be a way to reroute the termination to another location. We have an '08 MDX and haven't noticed the problem, knock on wood... .

yungone501

iTrader: (4)

No, there was only one vent in the rear. As a matter of fact, a later looked at some Acura factory body diagrams and confirmed this is the ONLY cabin ventilation duct.

As for others not experiencing the issue, be thankful. The heavy smell gives me both a headache and makes me sick at my stomach. I did find two other TSBs that pertained to other "ventilation" issues that could eventually cause this issue to happen over time. One was a seal issue on the liftgate rubber and also an issue that involved the recirculation flap from the windshield cowl to not fully open and close when switched to and from recirculation/fresh air on HVAC system. Either one of these are possible failures that as I said could evolve into allowing the exhaust fumes to be sucked into the cab.

yungone501

iTrader: (4)

Excellent point and I've considered the consequences of doing this but quite honestly, I'd rather endure whatever else that arose from blocking off the duct than have to breath exhaust! :-)

I'm pretty sure that no moisture buildup would occur because when using defrost is turned on, so is the AC compressor which naturally removes moisture from the air...well, technically the evaporator does. This is why you see water dripping beneath the vehicle when AC is being used. I suppose you would be more likely to see issues with cabin pressures when opening/closing doors (especially towards the front of the vehicle) or driving with the windows cracked.

larso1

OK, here's something else to consider.... outgassing of the plastic surfaces in the interior during the summer months. You may notice you have to occasionally clean residue off the interior surface of your windshield, usually from the dashboard. Some people are very sensitive to the chemicals floating around as a result of this, and fresh air makeup is the only source of dilution. Just something to consider. In modern office buildings with sealed windows and unbalanced HVAC systems it can lead to what's called "sick building syndrome." It's a problem either way.. exhaust gas or outgas...

yungone501

iTrader: (4)

Wow bro, youre filled with all sorts of excellent points tonight aren't ya? Lol...

Now, consider this: you can never assume that there is an air tight, vacuum sealed separation from the outside of any vehicle...even if this duct is blocked as it was in my vehicle. It does serve a purpose but more than likely (as most designs on most cars) it's an overkill in its purpose. This overkill is a good things because it gives room for error, that's its purpose after all. I have to respectively disagree in your points made though. Two reasons:

1. The cabin air filter- this is not just ANY old filter by design nor by its effectiveness. These things are made to completely (to an extent) purify the air that's passed through it. It removed many things in that process. Most are actually comparable to HEPA filters. This filter in conjunction with the evaporator (to remove moisture) can be highly effective in preventing any bacterial growth and/or "dirty" air. Besides, the doors are opened frequently enough to prevent the occurrence of a stale air condition.

2. The residue you are referring to left on your window is actually left by the accumulation of moisture buildup and then evaporating and leaving behind the minerals and/or dirt and dust that was in the moisture. That's why you generally see moisture buildup after the car has set overnight or upon warming the car up faster than the window can warm up. This is called the condensing point. The temperature at which the moisture in the air converts to a liquid state and normally settles on the "coldest" surface. That would be the glass due to glass being a poor conductor of heat itself.

In conclusion, you wouldn't risk getting sick for plugging up a small hole that wasn't essential to begin with. I studied the laws and physics of HVAC for over 2 years and that's the profession that actually led me into my current field: Automotive electrical technician. I gained a majority of my electrical background from my HVAC profession. I'm only mentioning that so you don't think I'm blowing smoke about anything said here.

Don't get me wrong here, I love my MDX! Never had a better vehicle in my life!

larso1

"1. The cabin air filter- this is not just ANY old filter by design nor by its effectiveness. These things are made to completely (to an extent) purify the air that's passed through it. It removed many things in that process. Most are actually comparable to HEPA filters."

Actually, that's all it is. A High Efficiency PARTICULATE filter... only removes dust, dirt and pollen. It has no other "purification" capabilities such as removal of gases, odors, etc.

"This filter in conjunction with the evaporator (to remove moisture) can be highly effective in preventing any bacterial growth"

Good luck with that.

"2. The residue you are referring to left on your window is actually left by the accumulation of moisture buildup and then evaporating and leaving behind the minerals and/or dirt and dust that was in the moisture."

No, the residue I'm referring to occurs mostly during hot dry months...... especially here in So. CO. Outdoor air temps over night here typically drop to around 60-deg.F. during the summer, well above the dew point temp. No latent heat of condensation happening here. You can check any psychrometric chart to confirm this fact.

"That would be the glass due to glass being a poor conductor of heat itself."

Maybe on your planet, but here on Earth glass conducts heat very well, from inside your house right out to the cold outdoors. Which is why they invented thermal pane glass with an interstitial air space, to increase thermal resistance (R-value). Ever cook with glass ware? Check out the R-value of glass relative to other materials.

"In conclusion, you wouldn't risk getting sick for plugging up a small hole that wasn't essential to begin with."

"......wasn't essential" is your unqualified opinion. It may work out just fine for you to cap it off, but it is part of the HVAC system for good reasons. The danger of exhaust gasses entering your cabin may very well trump the dangers and nuisance of moisture buildup and outgassing of interior materials. Personally, I would look for a way to extend the duct termination to a point away from the exhaust system if at all possible, so that you could have the best of both worlds.

"I studied the laws and physics of HVAC for over 2 years and that's the profession that actually led me into my current field: Automotive electrical technician."

HVAC engineering/design was a large part of my profession as a mechanical engineer.... 39 years, retired last week.

"Don't get me wrong here, I love my MDX! Never had a better vehicle in my life!"

We would agree with that...

yungone501

iTrader: (4)

Ok, everything you responded to except the fact of glass and it's heat transferring capabilities is a matter of opinion. But I have to say one thing and then I must move on: glass my friend is one of the best insulators in the world to heat. Why is that? It's a poor heat conductor. Its not the best don't get me wrong. Fiberglass is often used in walls of homes to INSULATE homes and protect them from heat intrusion. ;-)

db22

It seems to me that the issue is rare, if was common then carbon monoxide poisoning of all MDX drivers would have created a fair sized stir among the lawyers and Acura would have been bankrupted years ago.
If you accelerate hard then I am assuming that you are moving forward and that the gasses exiting the pipes is being left behind the vehicle. How do the gasses go forward to get inside the vehicle? If the issue existed while standing still then I could understand the complaint better.
OP - have you absolutely concluded that there is not an exhaust leak further forward that manifests under hard acceleration?

yungone501

iTrader: (4)

I explain doing a leak test in the exhaust system on the first paragraph of this thread. I even tried the smoke test with the exhaust both hot and cool just in case there was any leaks made with the fluctuation in the metal...no difference.

rcy

It's not even a HEPA class filter. It's just a basic filter, similar to the one that filters air for the engine - removes dust/pollen. It may or may not have carbon in it to help with odours, but it's nowhere near a true HEPA filter.

http://en.wikipedia.org/wiki/HEPA
______________________________

It's in the evaporator that bacteria and mould develop BECAUSE the evaporator removes moisture from the air. It's this moisture, left on the evaporator after the system is shut off, in a nice dark, warm environment (perfect conditions for bacteria and mould) that is the problem. My previous vehicle (Lexus RX400h) actually had an anti-bacterial coating on the evaporator to prevent this. The only problem was the coating, over time, would start to flake and many 2nd gen RX owner's had dandruff all over the dashboards, clothing etc.

db22

It is not easy to do a smoke/leak test while travelling under hard acceleration so I assume your test was done while standing still. Therefore the exhaust gases must comeout of the exhaust pipe and go in the direction of travel to get into the plenum?

dominik331

I've been scratching my head over this and wondering exactly the same thing.

larso1

I understand from reading this thread that there is a flapper (valve) in the air duct? My question is ...is there a motor operator on this valve? Does the ECU control this? Could it be malfunctioning? I find it very strange that most people do not have this problem, including me. If it is supposed to be closed only during full exceleration, and it isn't, then that would explain alot.

ten15magnet

Thanks for taking the time to figure this out. I have a 2010 Tech & RES and when I get onto the highway I am pedal to the metal. Then the smell comes. I will be taking the MDX to the dealer with your findings and hopefully they can prevent the exhaust from entering the vehicle under full acceleration.

itjbmcp

I was just wondering if the cause and solution would be relavent on a 2010 model?

I have the smell as described and high CO in the cabin when in recirc. I've measured over 100 PPM which is crazy for inside a vehicle at freeway speeds. I've been fighting with dealer and acura and they can't find anything wrong.

I did just look at the access cover at it is full of dust in that compartment so I am guesssing that your investigation of the cause is still correct for me ?

Your thoughts and I am very much appreciative of your wonderful writeup on this.

Thanks

itjbmcp

I was working thru proving the issue as discussed and found two rubber sheet metal plugs that are missing directly in front of the vent that was described. The holes lead directly into the cabin or directly in front of the cabin vent. Huge hole exhaust coming straingt in and also a signficant amount of dirt in the fuse box area. One of the plugs was setting on top of the back part of the splash guard. That is what tipped me off.

larso1

Sounds like you found the REAL problem and solution to the exhaust smell. Congrats! Let us know if it really does fix the problem...

itjbmcp

I've attempted to show the hole this is on the passenger side. You can also see the one way vent that was decribed by the original opening thread. I still am so thankful I found this thread that allowed my to solve this ---- problem.

rcy

That hole is huge...

Could it be any of these parts?

http://www.acuraoemparts.com/delray/...All&vinsrch=no

Or these two at the back..

http://www.acuraoemparts.com/delray/...All&vinsrch=no

itjbmcp

This is for the Body plug described

GROMMET, SIDE PANEL - 2010 ACURA MDX
(74514-STX-A00)

Item 9 on the diagram

http://www.acurapartsnow.com/parts-c...per/grommet-rr



This is for the Vent as described earlier in this posting

Item # 37 in diagram

http://www.acurapartsnow.com/parts-c...nel-roof-panel

lanceb1b

Thanks to op for the vent info, our 2010 has done this from day one, been to the dealer twice, "They could not reproduce problem." Taking a looksee tomorrow.

itjbmcp

Be sure to have them check the body plugs right in front of the vents. They let air directly into the cabin. I have a 2010 mdx both have fallen out. Look at the end of this thread for more info.

lanceb1b

Just an update, missing the body plug on drivers side, ordered part, dealer will call when part arrives, so they can install it. I'll update when it's done.

itjbmcp

Mine is in the shop waiting for me to drive the 60 miles to pick it up.

They had to glue both of my plugs to keep them from falling out again.

I will be testing immediatly after I pick it up with a Carbon Monoxide detector in recirc to see if the entire problem is fixed.

yungone501

iTrader: (4)

Wow, that's crazy guys. Good to see some progress. I actually came here to correct myself on a previously mentioned post. Somebody had asked if there any other vents and I at the time didn't see any. But then just a few days ago, I noticed another vent on the other side in the same damn place. Blocked that one as well and mine is still not smelling as of the first repair.

Glad to see progress, good luck to those at the dealer with this!

rcy

I figured there'd be a vent on both sides.

However, did you check to see that the body plugs mentioned in the last few posts were in place before you permanently sealed your vent? It seems more likely that these missing plugs might be the cause of exhaust entering the vehicle.

yungone501

iTrader: (4)

No I haven't. But sealing both vents seems to have corrected my issue atleast. But, if it reappears, I know what route to take. :-)

Has everyone that tried either fix had success in eliminating the issue?

db22

I still don't know how exhaust gas comes out of the tailpipe at freeway speeds and enters anything ahead of the hole in the pipe unless there is an exhaust leak somewhere ahead of the hole plugs.
If you floor the pedal getting up to speed on a freeway then the car in front of you is probably doing the same. Maybe it's from the car in front and the guy behind you is wondering where the leak is on his car when the smell is coming from you?

itjbmcp

My vehicle has been returned the body plugs have been replaced and glued in this time. I've tested the car with extreme acceleration and high loads and no smell. The dealership is very embarrassed that they didn't check this in the first place. Acura is blaming the dealership even though the dealer was working directly with Acura. It is a shame we had to find the problem ourselves. I am very disappointed in Acura's response to the high carbon monoxide that I reported inside my vehicle.

db22, you should have seen my CO detector when I was measuring in the compartment mentioned earlier above the body plugs and vents. It spiked unbelievably high when accelerating. (>300PPM) Most vehicles’ have a low pressure swirl behind them.

Again I can’t thank “yungone501” enough for getting me looking in the right area.

rcy

Probably the same reason that exhaust can enter the vehicle if you drive with the hatch open..air swirling around etc.

rcy

Looks like itjbmcp had the body plugs replaced and the problem is gone.

I know you solved your problem in a different way, but I'd be concerned about those vents being permanently sealed.

db22

You guys are lucky that the car exhaust stinks because CO is odorless and creates permanent brain damage. If this had escalated then Acura would have been in really deep do do.

itjbmcp

That is my concern as well because if you have the system in “recirc” and are driving against a high head winds, towing, or driving in the mountains the CO does build up. I documented that. The only time it really stinks is when you perform hard acceleration and there is some un-burnt fuel. I did just submit a NHTSA complaint since I see here and other places on the web of similar complaints. I being a father that had a 3600 Mile summer vacation with a 1.5 year old am less than thrilled knowing CO was in the cabin while driving across the mountains.
.

Izzy-Type-S

iTrader: (1)

Ours has an exhaust smell and horrible sound on cold start especially now that nights are getting down in the 30s. Cars are garage kept but on cold starts I get this loud rattle and exhaust smell. Dealer says they can't replicate even when they kept the truck overnight WTF? Local exhaust shop told me it was an exhaust leak by the manifold, have u guys encountere this?

aka

I am in the process of working with Acura to get this very problem fixed in my 2010 MDX. So far the dealer is at a loss to figure this out. The rear plugs are in place - but still getting measurable CO (yes, bought a meter) during heavy acceleration . District rep seems to have never heard of this issue, etc etc.
Can you please point me to the TSBs you mention, youngone - could be very helpful. I really need to get this solved.
I suspect there is a 'forward' cabin seal issue (the windshield cowl recirc flap makes sense) as well as an exhaust leak despite the service guys' claim no exhaust leak...
Very disappointing as I really like the vehicle aside from this major concern.

3rdpig

I've been getting that foul smell after acceleration in my 2015 MDX. I'm going to check if these grommets may be missing too.

vwin8

My dealer just fixed this same issue on my 2012 MDX, there's a TSB for it.