Black powder coming from car?

[ZEEM3R]

Hey guys, so I have a somewhat weird problem and Im not sure whats causing it. Ive recently noticed that the rear of my car gets dirty VERY quickly due to some black dust/powder that accumulates rather rapidly. Today, I noticed that the same black dust is also on my driveway and from the way I park, it seems like its coming from underneath the car. Theres no fluid leakage.. just black dust/powder.

A quick history on my car: the primary and secondary cats that were originally welded together were cut so I could match and mix them with aftermarket test pipes and/or x-pipes. Few months ago, I welded them back together and put them back on. So, the only current modification is a CNT exhaust. I have an AA drop in filter to round up the performance mods.

I have a few theories on where so much powder is coming from but hopefully someone can help me:
1. The body shop that welded and put the cats back together didn't do something right and so the powder is coming from a leak in the exhaust system..
2. My CNT exhaust is responsible (would explain why the rear of the car is getting dirty so quickly) but I noticed some of the powder on my driveway was where the front of my car usually is so idk...
3. This one right now makes the most sense but also not the most sense. I parked my car parallel to the areas where the black powder was and I noticed that the areas of most accumulation seem to line up with my tires.. Im currently still running Bridgestone winter tires cause I just haven't had time to put summers back on. The rims are black rims which I assumed were painted black. Could it be that driving winter tires in summer weather is causing the powder to form?
4. Or.. is it just excessive brake dust? If it is, how do I stop it from turning my car into a half-white, half-black M3?

Thats all I can think of right now.. hopefully someone can help cause Im tired of washing the car and my brand new driveway is turning from orange to black smh.

If anyone would like pictures, let me know. I noticed all this at night so in the morning Ill investigate some more.

[roastbeef]

its a crap shoot until you get under the car on a lift. maybe have it idling while on the lift? not sure.

i saw a newer (2014ish) 335 that appeared to be stock at the dealership service bay. it sounded rough as it idled, and the tail pipes sputtered out black soot/powder every few seconds. i'm not sure what exactly happens when catalysts fail, but if i had to speculate, i would say they were probably the culprit.

[Tracyis300]

It would help if you could show pictures of it?!

[ZEEM3R]

Originally Posted by roastbeef

its a crap shoot until you get under the car on a lift. maybe have it idling while on the lift? not sure.

i saw a newer (2014ish) 335 that appeared to be stock at the dealership service bay. it sounded rough as it idled, and the tail pipes sputtered out black soot/powder every few seconds. i'm not sure what exactly happens when catalysts fail, but if i had to speculate, i would say they were probably the culprit.

If the catalysts failed, do you know if the CEL light would turn on? The car is not tuned.

Originally Posted by Tracyis300

It would help if you could show pictures of it?!

Haha give me a break.. Its 1am in NY and I had a long day!

[Nixta_72]

I've always assumed this to be brake dust build up. The entire car rear of the front wheels accumulates it on mine. I just want to know a safe method to clean it off...standard touchless car washes don't seem to do the trick.