Vehicle is a 1999 GMC Envoy 4x4 130k. When starting the vehicle and upon heavy throttle, some liquid brown chunky shiit shoots from the tailpipe. What could this be??

 

Are you loosing antifreeze? Or Could it be just rusty water? New fuels with ethanol will create more moisture in the exhaust. I believe the factory muffler has a very small hole drilled in the bottom rear to drain this moisture but if it gets clogged it will build up and come out of the tailpipe.

 

Overnight water condenses in the warm/hot tailpipe. When you start the vehicle it blows out. It should stop when the engine is warmed up as the water then turns into steam instead of blowing out as a liquid. Unless you are losing coolant it is nothing to worry about.