What if I cut the cats out altogether, leave the front 02 sensor, and then they make a rear 02 sensor that will read clean as I understand it...
The ECM will bust you for that...The ECM (Engine Control Module) works like this:
- it bangs back and forth between 1) too lean, where the upstream O2 sensor reads about 0.0V, and 2) too rich, where the upstream O2 sensor reads about 0.7V - the waveform looks like a square-wave.
- The cat is supposed to (very temporarily) store a bit of the excess O2, then a bit of the excess fuel, which then reacts with the opposite condition coming along soon. So...the cat is supposed to sort of "low pass filter" the exhaust gas stream, outputting a gas stream with an average - nearly balanced fuel/air mix. - The waveform looks like a slow triangle wave, or at least a ramped trapezoidal squar-ish wave.
The downstream O2 sensor should read about 0.4V (balanced) at least sometimes. With no cat there, or - effectively no cat, because it has become old / coated with ash residue, then it is essentially a tube and not a cat anymore.
- Then the ECM will throw an OBD2 code saying "catalytic converter efficiency low" (if the downstrean signal also looks like a square-wave).
- You can actually see the waveforms of both upstream and downstream converters and see this stuff going on, and conclusively diagnose these things.
- With an inexpensive plug-in bluetooth OBD2 reader and the "TorqueLite" Android App. I use an iPhone, which, unfortunately has no OBD2 reader App available - I keep a somewhat obsolete Android phone around just for this necessary(once-in-a-while) tool.
Of course - if you have electronics skills, you could build a little "downstream O2 sensor" simulator - if your are really that motivated NOT to simply have it all work the way it's supposed to...I guess.
) 
