Truck is a 1988 d100 with a 3.9 manual. I have had a smeel but hard to say what it smells like. When i let it warm up for maybe 3 mins i get black soot on the ground. Can my converter be going bad, the muffler and converter is original. If it is bad what would the shop do with the smog stuff,still connected but not working. I would want all of the old parts. A guy i work with said use a pipe instead. thanks

 

if it is bad i would just leave it there. black soot on the ground seems normal to me. i would also guess until your truck reaches full operating temperature it could run rich until the o2 sensor starts controlling the fuel to air ratio.

 

If the converter is bad will t affect my mpg or damage the motor?

 

If its just old/burnt out, it won't hurt anything. It just won't pass a smog test. If it is clogged, it will hurt MPG and power. You'd know if it was getting clogged, because you'd be cursing every time you saw a hill coming up. It doesn't sound like its clogged though. If I were you, I'd just leave it be. You won't gain anything from bypassing it.

 

I just replaced the entire exhaust on my 90 D-150 including the cat and 02 sensor and it cured the soot problem. At startup mine was running rich and idling kind of rough until it warmed up and it looks like since the cat was mostly plugged the O2 sensor sooted up and stopped working.