Article on how to diagnose bad cats:
http://answers.yahoo.com/question/index ... 830AAzOPz0
The front cats are the two to be concerned with (there are 4 total) but the front two cats are between two O2 sensors. FYI, Advance Auto and Auto Zone are no help. Advance was going to sell me a rear cat and it wasn't labeled front or rear. When I asked them why that seemed to be the part # to the rear cat made by Walker they just told me they were sorry they had no more information.
Walker, Eastern Catalytic, and Davico are three reasonably priced brands I've been able to find (Magnaflow are expensive).
Here are links to front and rear cats from the Walker website and a few links to buy the cats. I would make damn sure my O2 sensors were all good, have my plugs replaced, and check for vacuum leaks before putting cats on. One way to check if a cat is functioning is to point an infrared thermometer on the front of the primary cat and on the rear of the primary cat and their should be about 100 degree difference in temp.
Front Driver
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE
Front Passenger
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE
Rear Driver
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE
Rear Passenger
http://catalog.walkerexhaust.com/catalo ... tus=ACTIVE
These Davico are the cheapest I've found from a reputable dealer:
Davico Front, Driver Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 18218.html
Davico Front, Passenger Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 18219.html
Eastern Front, Driver Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 40710.html
Eastern Front, Passenger Side Catalytic Converter
http://www.autopartswarehouse.com/sku/N ... 40711.html
Here's a site that also sells Walker cats (cheapest on Walker rear cats):
Front Driver
http://www.woodys-auto-supply.com/auto- ... =WAL-16468
Front Passenger
http://www.woodys-auto-supply.com/auto- ... =WAL-16467
Rear Driver
http://www.woodys-auto-supply.com/auto- ... =WAL-16400
Rear Passenger
http://www.woodys-auto-supply.com/auto- ... =WAL-16399
Article on how to diagnose O2 sensor problems:
http://www.aa1car.com/library/o2sensor.htm
A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor output to drop to its minimum (0.1v) value. If the sensor does not flip-flop back and forth quickly enough, it may indicate a need for replacement.
My issue is my primary cats both show the 100 degree difference between front and rear leading me to believe one or more of my O2 sensors are bad but there are specific codes for bad O2 sensors which I'm not seeing leading me to believe I have a bad cat. It's a very tricky thing to diagnose if you don't know what you're doing. I wouldn't even know where to begin to hook up an oscilloscope like recommended in the article above.
I bought an OBD II code reader/diagnosis tool to record readings from my O2 sensors and this is what I saw. I was parked and gave throttle up to about 3k~4k RPM and back down to idle repeatedly for about 30 seconds and this is the readings of my O2 sensors.
If I'm reading this correctly, Sensor 1 bank 1 (drivers front O2) and Sensor 2 bank 1 (drivers rear O2) have bad readings.
To add to my confusion is I believe if the ECM senses that the motor is running too rich in the case of a bad cat, the ECM will lean out the air/fuel ratio which would also affect the readings of the O2 sensors. That seems to me to make it even harder to tell whether an O2 sensor or cat is bad when the O2 sensors could be self-adjusting for a bad cat.
Furthermore, my vehicle gets the same MPG it has always gotten and doesn't run poorly or idle roughly.