2004 MCS - 136,000 miles. The mileage may be relevant.

I was driving home from work on Friday night when I noticed that the BMW in front of me had an unusually 'sporting' tone to its exhaust. The BMW turned, and the sound came from an Accord, instead!

Wised up, windowed down, and it was clear that I was the noise maker. Within a block or two, it sounded like I had no exhaust at all. Another mile or so, and the sound was nearly back to normal, but with an extra 'burr' to the sound.

In the old days, this meant the muffler was going. Nowadays, who knows? The sound seems to be coming from up front, but I am notoriously bad at localizing sounds.

Yesterday, I had to drive during the monsoon and it did not sound too bad until I drove through standing water that was a few inches deep. The sound immediately went from slightly louder than usual to almost no muffler at all!

I parked for an hour or so, and when I drove it again, the sound was nearly back to normal. Would someone with more of a clue than me (which may be almost everyone) care to offer a guess as to what is going on? I live some distance from a dealer, and have very little free time on my hands during the times that good mechanics are open for business, so I'd like to try to get it to the right place on the first try if at all possible.

My thinking is that something is pulling apart, then sliding back into place, hence the dramatic rise and fall in noise levels, esp when driving thru standing water. What might that be, and what should I expect to do about it?

The car has 136,000 miles, a stock exhaust, and has received no maintenance to the converter nor the O2 sensors, if that helps.

 

Jack up one side of the MINI, please use jack stands, then take pics and post them of the WHOLE system. I bet someone will see something to give you a place to start.

 

That flex joint in the stock header might be torn.

 

I live in DC proper, so doing that on the street is gonna be difficult, if not impossible.

I drove the car again today. I usually drive with the windows up, and it is amazing just how much louder it is with the windows down.

I heard a distinct metal rattling sound on a couple of occasions when I put it in reverse. More fuel for my loose part theory. Wish I knew how these parts went together, or if there even is a part that can come loose like that. On my prior car, back-pressure in the cat system caused the whole connection to pop off, but even that is possible on this engine, I know it can't have happened the same way here, given the way the noise level comes and goes.

 

Here's some pics to help, but sounds like you need to get in on a rack and let a wrench look at it soon.

Here's a link to pics of the system. http://www.realoem.com/bmw/partgrp.d...id=48021&hg=18

If you do need a replacement let me know I can get you most of the the after market catback and header systems.

 

Thanks for the diagrams. Anyone have wrench suggestions in DC or MD suburbs of same? The dealers and Lucky Dog are all a bit of a haul from my current job in Rockville.

 

Obviously something is coming loose with the exhaust. When you hit the water, a hot part gets cooled real quick & contracts. Used to see this happen with older cars where the tailpipe leading to the muffler is just clamped over the header pipe. Hit a big puddle and the rear pipe just comes right off. [FONT=Arial]
[/FONT]You might try a muffler shop. At least they could get it up on the rack & take a look. Might be loose at that flange where gasket #4 in the pic is.
If you are lucky, maybe all you need is a new gasket & to have your #5 nuts cinched down.
If not? Let us know.

 

That is the sort of thing I was hoping was wrong, but my mechanic has other ideas. Things are broken at the juncture between the exhaust header and the cat converter, with the result I get to replace both, for upwards of $2K. I've decided to do a bunch of other stuff at the same time, with the result that I could be looking at my first $5,000 repair bill!

 

Whoa! Slow down.... Do NOT spend that kind of money on an OEM header/cat. There are MUCH less expensive and MUCH BETTER options available (like, less than $1000 for a better header... Revolution Mini Works...) There are also probably used OEM ones available from folks who have taken them off to replace with aftermarket if you really want OEM... post on the "wanted to buy" on the marketplace forum here!!!

 

That's just way out of hand. I agree with BlimeyCabrio. Or, .. can't someone weld this stuff back together? Thousands of dollars for an exhast just seems crazy to me. Your money, I guess.

 

PM Sent, $2K is way too high.