i just bought a 98 chevy with a 5.7 in it. not much later it started to blow black smoke out of exhaust. cylinders 2,4,6,8 all had missfires also. swiched the O2 sensors around and the miss fire switched sides to the odds. So replaced O2 sensor and ran fine and no more codes popped up. about two days later light came back on and can see black smoke starting to come out of exhaust. the side that is bad has a catalytic converter that has a leak also. please help!!

 

try cutting out/replacing your cats.(magnaflow direct fit dual cats run about $360.)a good options. clean all O2 sensors. check and replace spark plugs with premium plugs. run it and see.

 

thanks i will give that a try