most likely, too much fuel.
Heat, unburned gasses, carbon soot.
The emission output at tail pipe can be used to check causes of little air or too much fuel. The emission output can check the levels of water vapor, sulfur dioxide, hydrogen and particulate carbon soot.
Unburnt fuel
Soot, as in chimneys, is just ashes. The word is majivu, the same as produced by by a cigarette, fireplace, or a pipe. CORRECTION: Soot = masizi Ashes = majivu
burning oil
not goot
aerosols and soot from air polution
Your in a high condensation area and it has collected in your exhaust system and causes old mufflers and exhaust system to rust.
Flomasters
Yes they have them.
Explain what it is doing! is water coming out of the tail pipe? do you see white smoke coming out of the tail pipe?
That big pipe on the bottom of your car with the cat and muffler on it, ends in a tail pipe, squirts pixie dust.