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View Full Version : Exhaust stink inside car, Part 3



4bagels
07-20-2010, 09:57 AM
Some more reading for those of you with exhaust fumes getting into your car, and a new discovery...

First, I keep celebrating victory over this problem only to find out that it is still there. Part 1 discusses getting rid of the exhaust leaks themselves. Part 2 was about the air extractor vents in the trunk, which I now believe are fine as long as you find them to be in the closed position.

So on to the new discovery: I found a very unexpected way that fumes from the exhaust tips can make it right back into the car! Believe it or not, it's the frame rails! If you look under the rear bumper cover, where the bumper shock enters the frame rail, it's a wide open entry to the frame rail, which is only a few inches away from the exhaust tip. So when the car has negative pressure (like driving with the windows or sunroof partially open), air is trying to find it's way INTO the cab, and this is one big spot where it sucks air from, and it's got to suck exhaust fumes since it's so close to the exhaust tips.

If you think I'm crazy, here's how I verified it. With the car off but the key on, I turned on the hvac to full speed, fresh air mode (not recirc), closed the windows and doors. I had already plugged up the 2 air extractor vents deep in the trunk. I went under the car feeling for air escaping, as it is now trying to find it's way OUT of the car. I found a few little leaks around the door seals, etc... And a few bigger leaks along the frame rails where there are drain holes, but the BIGGEST air leak was what I mentioned above, the very end of the frame rails under the rear bumper cover. I sealed off the holes with some sheet metal cut to size and some adhesive to hold it on. I just wanted to seal it off, I didn't want to make anything too robust as it could interfere with the bumper shocks in case of an accident.

It helped a LOT, but I want to drive it for a couple of weeks before I celebrate victory (again).

EErie B6
07-20-2010, 10:04 AM
you sure its exhaust, not pcv?

4bagels
07-20-2010, 10:05 AM
you sure its exhaust, not pcv?

Pretty sure it's mostly exhaust in my case. Have you had pcv fumes getting in?

EErie B6
07-20-2010, 10:09 AM
Pretty sure it's mostly exhaust in my case. Have you had pcv fumes getting in?

i had issues with my pcv lines a few months ago, where the line cracked not far off the back of the head the breather air now leaking to the atmosphere would be sucked in the intake for the HVAC system.

its actually a somewhat common problem.

4bagels
07-21-2010, 06:48 AM
Quick update... after a few days driving with the ends of the rear frame rails "capped off", I haven't been getting any exhaust fumes inside the car anymore. I would definitely say give it a try if you have annoying exhaust fumes that you can't get rid of when the windows or sunroof are open. Separately, if you get fumes when the hvac is in fresh-air mode (not so fresh), try replacing the rubber seal that goes along the top of the firewall.