I replaced the cat and both o2 sensors and cleared the codes and I am still getting the p0420 code on my 99 ex coupe. She is also bogging out on me every morning when I leave the driveway. It does this when I go into second but if I push the clutch in and rev it it goes away. I am trying desperately to get rid of this.

Please help!!!!

 

Look carefully for an exhaust system leak around or between the primary and secondary O2 sensors.

 

Will do. Should I inspect the exhaust system upstream too? Would this affect the readings?

 

If your primary O2 sensor is located in the exhaust manifold, then it is as upstream as you can get. If not, you should theoretically not have to look upstream of the primary O2 sensor as P0420 is determined by a comparison of readings from the primary O2 with those from the secondary O2 sensor.