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Discussion Starter #1
I have an 98 s10 ext cab 4.3L pickup with 305k miles. I got this code two weeks ago. I cleared it twice and it still comes back. I hooked up a scanner after driving for 45 minutes at highway speed to warm up the cat. Here are some of the parameters:

STFT B1 - cycles between 0 and 3 but stays primarily between 0 and 1
STFT B2 - same as above.
ECT - 90 Celsius
Oxy Sensor B1 S1 - cycles between 100mv-800mv
Oxy Sensor B2 S2 - same as B1 S1
MAF - 5 g/s
MAP 34 kpa
Now the interesting value that has me perplexed: Post Cat O2 (B1 S3) sensor cycles between 50mv-75mv. From everything I've read the post cat O2 sensor is showing that there is nothing wrong with the catalytic converter. I've heard that the cat converter is designed to last the life of the vehicle if the engine is properly maintained. What are the chances that the cat converter is really going bad. I'm the original owner and I've replaced plugs, wires, distributor cap and rotor, o2 sensors, egr and pcv valves every 50k miles. Mobil 1 every 3500k-4000k miles.
 

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1997 S10 5.3L
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You need to look at the cycling speed of the post cat O2S. It's even better if you have a graphing scan tool. It should be long swooping sweeps back and fourth. Much slower than the upstream sensors. If it's switching rather quickly, that would be an indicator that the catalytic converter isn't gathering oxygen as it should and could be clogged.
 

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Discussion Starter #3
You need to look at the cycling speed of the post cat O2S. It's even better if you have a graphing scan tool. It should be long swooping sweeps back and fourth. Much slower than the upstream sensors. If it's switching rather quickly, that would be an indicator that the catalytic converter isn't gathering oxygen as it should and could be clogged.

I replaced the post cat O2S with a new AcDelco part # AFS 105. The old sensor was a Delphi part. Not sure how many miles maybe 60k. I also replaced the EGR valve which had over 150k miles on it. Knowing how these engines have issues with carbon build up on the EGR valve and pipe. Cleared code for the fourth time and drove 200 miles. So far so good. No codes.
 
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