Cats? 
Black soot on rear end
"AlohaC5" Senior Member
Joined: Jun 2003
Posts: 3,562
Likes: 44
From: Madison, AL
I have the same thing going on. I know my new 383 is running richer than my previously stock LS1, which is fine. However, I'm not sure if the "black soot" is coming from something else or not. Makes a mess of the exhaust, rear end and garage floor where I start it up.
Safety Car
Joined: May 2003
Posts: 3,814
Likes: 105
From: Dearborn Heights Michigan
My guess, and I am not totally sure, is that much of this is brake dust. My 00 Yellow Coupe gets this black dust behind the front wheel openings, behind the air vent on the front Fenders, behind the rear wheel openings and all over the back especially the tail light depressions and license plate area. Most light colored Vettes I look at have the same patterns. I have given up trying to stop it and just wipe it off every time the car goes out.
Fred
Fred
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,625
Likes: 1
From: Rhode Island
I watched it today when it was cold. I let it idle and it is from the water that is generated from the cats. After running it hard there is a lot of carbon in the exhaust. When the water goes through the pipes, it takes some of the carbon with it. I could see little black droplets of water shooting out the back. After it warmed up, the water stopped coming out, at least while it was idling. I just had it dyno tuned and it also did it before H/C and dyno tune. I have a catch can and a valve cover vent.
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Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,625
Likes: 1
From: Rhode Island
Originally Posted by FKING1
My guess, and I am not totally sure, is that much of this is brake dust. My 00 Yellow Coupe gets this black dust behind the front wheel openings, behind the air vent on the front Fenders, behind the rear wheel openings and all over the back especially the tail light depressions and license plate area. Most light colored Vettes I look at have the same patterns. I have given up trying to stop it and just wipe it off every time the car goes out.
Fred
Fred
Drifting
Joined: Nov 2005
Posts: 1,406
Likes: 0
From: Dallas Tx
The same thing happens on my 99 but i'm not running cats. Usually the exhaust gets cleaner at idle after the car is running off of sensor data. Before that point i believe i heard somewhere that it's running at somewhere near 10 or something as far as how righ it is. Which is why it puts out more noticable exhaust moisture and black smoke when you're on it. You'll get carbon build up there no matter what. The only thing that will minimize it is to get your car tuned leaner and to keep your foot off of it. Niether of which i reccomend. I just say keep cleaning it and have fun driving it like you stole it 
Shane
Shane
Melting Slicks
Joined: Feb 2001
Posts: 2,804
Likes: 358
From: Northville, MI
I bet if you were to hook up scanning software you would find your are running rich and timing is being retarded. The only way to know for sure is to scan. Find someone near you who has it and find out.
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,625
Likes: 1
From: Rhode Island
Originally Posted by FKING1
If it's not brake dust,where does the black dust on the front fenders and fender air ducts come from?
Fred
Fred
Le Mans Master
Joined: Dec 2000
Posts: 9,918
Likes: 1,879
From: Hot Springs AR
How long are you driving your car on a given trip? With that much water coming out (and this is the season to see it), I'm wondering if you're driving your car long enough to get your hi-flow cats up to temp. If they're cold they won't do their job very well and you could start seeing that carbon sooting.
It would be interesting to see how bad it gets if you go run your car for 15 minutes or so, leave it running, wipe the rear off then go drive again. If the soot goes away then we can start aiming at the startup enrichment/cold cats scenario.
HTH, and have a good one,
Mike
It would be interesting to see how bad it gets if you go run your car for 15 minutes or so, leave it running, wipe the rear off then go drive again. If the soot goes away then we can start aiming at the startup enrichment/cold cats scenario.
HTH, and have a good one,
Mike
Thread Starter
Melting Slicks
Joined: Sep 2005
Posts: 2,625
Likes: 1
From: Rhode Island
Originally Posted by Cajundude
Did you rub it? Is it soot or oil? Could be one of the covers/side seals on the diff.