My friends car will barely idle. It is hard to rev it at all. The exhaust has black smoke and there are pieces on the ground after its sits idling and the attempting to rev it some. I think cat but maybe someone has a better idea. Thanks in advance. It appears to be running rich if this helps.

 

Sounds like the rich condition has clogged the cat.

 

your cat(s) sound to be clogged and breaking appart inside and firing off into your muffler,disconnect your y-pipe before the cat and see if it runs better

 

Get a soft mallet and lightly tap on the cat to see if it rattles like there are alot of little pieces in it. This happen to me but it only rattled and did not spit out chunks. The guy that replaced my cat said that since my car was lowered the cat gets splashed by water and it is very hot so this heat/cold breaks down the material inside and it was the orginal cat, so he said. Good luck

 

No cat. I thought that too until i looked under the car.

 

Was the cat recently removed because it was plugged? If so, chunks of the cat could have blown back into the exhaust. This happened to me.

 

Well i looked under the car and could barely see anything. Its 3" off the ground and noticed nothing. I then jacked it up and found the cat. The thing is not where it was from the factory so i was looking in the wrong place. I had cut the exhaust pipe in the rear right before the muffler and started the car. I got chunks as big as quarters! I then stuck an old FMU on that i had for my car and ran it with that. The difference was night and day. It would not run unless you kept the gas pedal down. It now runs at 1500-2000 rpm but it idles 5 times better without any gas. I figured the fmu was stuck close and no fuel would return to the tank. No black smoke at all and it sounds smooth. It is still on the rich side so i will replace the cat and muffler and go from there. Thanks all for the help