Exhaust smell with AC on?

944jeff · 10-12-2001, 06:50 AM

OK, first I've been putting up with a rattling in my exhaust, which is most noticeable at idle, for quite some time.
-Sounded like it was coming from under the drivers seat area and I figured it was a baffle that came loose inside the pipe. Just recently I'm getting a faint exhaust smell with only the ac on. (This is running in no traffic.) Any ideas?? I'd rather not fall asleep behind the wheel!

scottewid · 10-12-2001, 07:23 AM

I don't think running the a/c in itself would cause exhaust gasses to leak in when they otherwise wouldn't.

Turning on the a/c does, however, automatically engage the air recirculate i.e., the dampers in the fresh air intake under the windshield shut and block off outside air. You would think this would actually lessen the chance of exhuast gas getting in, but maybe it somehow affects air flow in and outside the car so that you get negative pressure in the cabin and suck exhaust in through a leaky rear hatch.....I'm out on a limb here, but stranger things could happen!

My 84 944 had a leaky gas cap and on hot days, you could easily smell the fumes when standing by the fuel fill door with a full tank. You didn't smell it when driving with windows open or shut, but if you closed the windows AND tilted up the sunroof AND had the cabin fan on low or off, you could smell it. Somehow that combination allowed the fumes to seep into the car when driving.

944jeff · 10-12-2001, 07:37 AM

I'm pretty sure it's only with the AC on. I've tried just the fan on or off and can't replicate. I will see if the air recycle button makes a difference. I usually run with it off. When I run home for lunch I will determine for sure. Thanks!

AFJuvat · 10-12-2001, 07:07 PM

Though I don't get it with AC, I used to get an exaust smell when the fresh air blower was on - turned out to be a small crack in the header ($30 weld job)

Another possibility - the rear hatch is notorious for not sealing properly - and letting in exhaust gasses.

AFJuvat

944jeff · 10-15-2001, 10:55 AM

OK, this is weird. Stills seems to be just with the AC on!! Nothing with just the fan, recycle button makes no difference. But... my hatch has started to rattle. This might be the problem. I'll have to search on the hatch fix and do just that.