I know black is unburnt fuel, but what could be causing the engine to not through out black smoke, but leave a light amount of black residue above the exhaust, it takes around 4000 miles for it to build and be an official black strip. It is noticeable around 2000 miles. The truck is a 1999 24V auto.. bone stock, even the air filter.

thanks,

Will

 

thats just normal for these diesels, you can shorten the tip a little to keep the build up off the fender