93 H22a civic exhaust smells like fuel

I smogged my car and barely failed a few hydrocarbons over the limit. Then I had someone weld a cat on to my car with an electric welder. They grounded the unit to the exhaust. Next day I drove smoothly to the smog place and smogged it again. #43 (fuel system malfunction or bad O2) engine light came blinking and i failed horribly. CO 7% and hydrocarbons like 300. So I am dumping lots of fuel.

Do you think these symptoms are caused by a bad oxygen sensor? Whats the best way to test the sensor without replacing it?

 

bump

 

check youtube i believe there is a way to test the sensor because i saw it not too long ago. i think u need some kind of device though to read it.

 

OK I'll check it out..thx