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abnormalmonk 11-02-2012 01:06 PM

Exhaust Issues
My girlfriend has an 01 7 Series, and when it is running, the smell in the car is very strong of exhaust, almost to the point you can't breath. Turning on vents and rolling the windows only makes it worse. Also sometimes the car will stall, and while it's running it sounds as though it is struggling.

My thoughts were a clogged catalytic converter, because when it turns off the car turns back on just fine. Any thoughts?

BMWFatherFigure 11-02-2012 10:11 PM

Start witha careful check for exhaust leaks. We will go on from there..............

mgoods50 11-05-2012 03:33 AM

There's a very easy way to test for clogged cats

remove o2 sensors- install bung / low pressure gauge. anything over about 2psi - you're clogged up.

cats clog for a reason- there's an underlying issue.

here's a link for setup and procedure :

I know the person who designed / tested this setup from online forums-- reputable source.

abnormalmonk 11-05-2012 04:55 AM

Does that sound like it could be a Cat clog? I only thought so because of the location that the smell is the strongest and it seemed possible that the backed up pressure from the engine to the converter caused the engine to stall, relieving the pressure, and letting the car start again.

Okay, I will check for an exhaust leak first, I'll try to find a good guide to do so, but if you should have a good thorough one you could post, it would be very helpful. Thanks for the info though!

mgoods50 11-05-2012 10:48 AM

Anything is possible, but I would first look for leaks as BMWFatherFigure suggested. The procedure for checking the o2 sensors is on the link. For leaks, generally speaking, an exhaust leak will at least make some additional noise and is best diagnosed on a rack with a funnel type mechanics stethoscope-- if not apparent enough to be clear from where the leak originates. That same tool will be useful for finding any future vacuum leaks as well. Where are the tail pipes on this one? Factory tucked under the rear bumper cover, or does it have tips showing. I ask because if the trunk ventilation flaps are malfunctioning, exhaust gas is basically sucked into the car. Is the HVAC control set to recirc or fresh air when the smell gets worse?

abnormalmonk 11-06-2012 10:21 AM

The exhaust pipes are factory, its a stock car. It seems to be worst when pulling outside air in i believe, I'll have to check again to be sure. Does that sound like a match? Also some of these devices are quite foreign sounding. Will I be able to get them at a local auto parts store?

mgoods50 11-06-2012 10:43 AM

Here's a link to a the most comprehensive set for $20: This is a cheeeep price too, they go for about $40 on ebay. Oreillys' I think is about $30

Not sure how much of a DIY'er you are- but if you got this one, you wouldn't need another- it has it all. Heck, I might even be interested in buying it from you used if you don't want to keep it, my set is a bit old anyway.

The O2 stuff is like finding a needle in a haystack. I don't know where Thomas (the guy from meurosport site) pieced it all together-- nobody keeps the stock of misc. fittings on hand that they used to. His is built right, he machines it-- and the part is compact. I'd look for a low pressure gauge (off the top of my head) on eBay-- something like would be used for ATV tires-- anything that would read 0-10 lbs should be just right, as it would indicate smaller increments more accurately.

I would definitely check the recirc / fresh air button-- see if that makes a difference. The fresh air is right there on top of the hood-- and shouldn't be pulling in exhaust fumes. If it's stronger when in recirc, I'd be more inclined to think perhaps there's something going on with the flaps in the trunk. By the way, in the rear deck-- right below the rear windshield-- that vents directly into the trunk, where those flaps are-- a "stuck" flap would allow exhaust fumes to creep into the trunk, and right into the passenger compartment. A really easy way to test this would be to sniff around as best you can near the rear deck with the doors closed, engine idling. If strong, I'd head into the trunk area to sniff around-- but that's not going to be as accurate since the exhaust is right by your shins-- and rising into your face and trunk area.

abnormalmonk 11-06-2012 12:59 PM

That flap stuck thing sounds most likely, after we ran it for a few minutes, her sister opened the trunk and said it smelled extremely strong in there.

mgoods50 11-06-2012 01:20 PM

Glad the diagnosing is revealing clues!

Next step is to check out the vent flaps. I don't remember exactly where they are off the top of my head- but if you carefully pull back the trim on the sides near the bumper you will likely see them right along the bottom / side area of the fender walls.

You'll need a flashlight- you're looking for something like this:
picture hosting

Don't spend too much time sniffing BTW- carbon monoxide will sneak up on you quickly--- AMHIK!

abnormalmonk 11-07-2012 08:46 AM

Okay and are these behind the trim in the trunk or where exactly are they located on the car. Or would I be better off going under it to find them

ALSO, would this cause it to stall at times?

mgoods50 11-07-2012 09:31 AM

Sorry about that, after I re-read, I realize I wasn't clear---

Inside the trunk, along the sides, close to the back of the car is where I believe the vents are located.

Would NOT cause it to stall-- that's why you'll need the O2 sensor pressure measuring thing.

abnormalmonk 11-11-2012 08:20 AM

I've been poking around in the trunk, and I can't seem to find the vent flaps. I tried googling it, but to no avail. Any tips on where to look more precisely?

mgoods50 11-20-2012 03:32 AM

Haven't been on here in a while-- did you ever find the flaps? Issue resolved?

Sorry, short of pulling the panels on my own car-- which I HATE to do because of some nerve problems with my hands, I can't remember exactly where they are. My gut tells me they are just beneath the rear-most trim in the trunk, along the sides-- if you pop the trunk, and start removing panels-- you can't miss them.

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