CatalyticConverterDeath

If you are getting a catalytic converter efficiency error code, there is a chance that your cat is no longer working properly. It could also be a bad sensor, wiring, etc.

What kills your cat? Usually it's excessive unburned fuel exiting the engine and heading down the exhaust to the converter. So before you replace the cat, find out what was killing it. These GM 4.3 engines can run poorly longer than most other engines run. You may not be getting a misfire code, but if your cat died, something caused it to die and it wasn't suicide.

Biggest failures are in the secondary ignition system. Plugs/wires/cap/rotor/distributor drive gear(pancake distributor disease). A lot of times you might not get a code until it's too late, or you might not even get one at all. Either way, if your cat is now dead, find the cause before replacing the cat, or else you will destroy another one, and the replacements generally aren't as fault tolerant as the originals.

If your cat has somehow gutted itself due to failure, or the rear most o2 sensor isn't seeing exactly what it wants to see, you will get a code about it.

To prevent the computer from setting the code, some people move the o2 sensor slightly out of the exhaust stream(for offroad use only):

Dorman # 42009 Spark Plug Non-Foulers http://amzn.to/2p4VsdD ($6.19 advance auto, can be had cheaper) work great on an o2 sensor if you take a 1/2inch drill down the center of it.

The tap on the left is for tracing the threads for a hitch. Just ignore that ;)

A quick drilling down the center and you can fit the o2 sensor in there, for off-road use only.

If you are having problems removing an already installed sensor, you don't need a special socket, just trim the connector a little bit and a standard box-end wrench will fit over it.

What if I am replacing my Oxygen sensor as well?

In that case, see the o2 sensor page as well.