I think I how to get rid of that pesky CEL from having a test pipe, and I want to see if you believe it would work. I say, put a resistor inline with the 2nd O2 sensor--Since the ecu checks for different voltage between the 1st and 2nd sensor, so if you vary the voltage between the two, it will send this signal to the ecu that the cat is working. Any thoughts? Or am i really off and this has been done?

 

It's not the voltage, it's the wavelength. If you look at the signal on a scope, the amplitude (voltage) is the same but the wavelength is different. It is shorter on the first O2 than it is on the 2nd O2.