This may be a bit late in the game, but I have to comment on the notion of the O2 sensor being for control of the catalytic converters. Catalytic converters are passive devices, responding to the amount of unburned fuel by catalyzing it with oxygen (hence, burning it). They are not a mechanical device - they are coated metal that causes a reaction when they come in contact with fuel. Air is pumped into the exhaust at a rate that varies with engine vacuum and rpms to provide the oxygen necessary for the second burn. So to make the statement that the O2 sensor controls the catalytic converter is simply untrue.The purpose of the O2 sensor is to monitor the oxygen content of the exhaust and adjust the fuel ratio accordingly to get the best rate of burn. The more O2 that's present, the leaner the mixture ( not enough gas to consume all the available oxygen during combustion). HOWEVER - the mixture will only be adjusted by the amount the ECU tells the fuel injectors to based upon input from the O2 sensor. Without the O2 sensor, one could program a set map into a Power Commander, but that would negate all the benefits of combustion monitoring that's designed to compensate for changes in temperature (in conjunction with the air temp sensor above the headlight assembly), or air pressure (sensor on each cylinder), etc. The map that is programmed into the ECU basically says at a given signal from the O2 sensor, at a given throttle setting and rate of increase ( hard snap, or steady cruise) then send this much fuel to the cylinders. Changing the "map" changes the ECU response to these variables.So, the bottom line is the catalytic converters are going to burn unburned fuel on their own - O2 sensor present or not. It's merely a function of the mixed-metal oxide coating on the honeycomb metal. The ECU will use input from the O2 sensor to make adjustments in the mixture, based upon the programmed map.To further support this, note that the PC V is available with an Auto-tune, which consists of a wide range O2 sensor, for continuous optimum tuning of the fuel mixture, based upon your map.(or the stock, base map for your setup).Finally, the popping that we hear in the pipe is a result of an overly lean idle mixture, not overly rich. The idle circuit uses a closed O2 loop ( so the sensor does not provide mixture correcting feedback), and the idle mixture is set too low from the factory to help reduce emissions. The pop is unburned fuel that accumulates and ignites in the muffler. This occurs when you roll off the throttle and it returns to idle position momentarily and the draw from the engine is not matched bynthe amount of fuel being sent to the cylinders. So the unburned fuel passes through and collects ( short term) in the muffler. To correct this, use the LinerWiki mod and richer the mixture. I had to do this when I drilled out my cat and drilled out the rear baffle, and the resulting increased flow leaned the mixture (in conjunction with a K&N filter). Hope this helps clear things up for anyone who stumbles across this thread. Not looking to start any arguments or cause any hard feelings - just trying to be sure folks know the truth.