Hello everyone, I bought a 97 Blazer 6 cyl (4.3 i believe) for my daughter, and we've had some work done to it. One of the main things was right after we bought it the Catalytic Converter disintegrated, so we had it replaced. I have since replace the Distributor also because the previous owner had broken off the tit to screw/tighten the distributor cap down. It's running pretty well now but since the moisture is staying out of the distributor but now it started kicking out the P0420 error. I'm assuming it is the O2 sensor since the converter was replaced my question is which one. From what I understand there is one behind the converter and one on the exhaust manifold.

Thanks for the help.

 

It is most likely the o2 sensor before or after the cat. You can check there functionality with a OB2 scanner. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady.
A code P0420 may mean that one or more of the following has happened:
[ul][*]Leaded fuel was used where unleaded was called for[*]An oxygen sensor is not reading (functioning) properly[*]The engine coolant temperature sensor is not working properly[*]Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe[*]Retarded spark timing[*]The oxygen sensors in front and behind the converter are reporting too similar of readings [/ul]