So I got my smog renewal notice and used my obd device to be sure monitors were all good, and catalyst was incomplete. So I have done about 5 drive cycles and nothing has changed. And I do not recall disconnecting the battery in over a year and no trouble codes.
So I checked the the downstream O2 sensors.
Normally they both should have similar traces like in the first pic. I blipped the throttle twice. In steady state throttle position I believe there should be a straight line.



So without touching the throttle I also saw this.



I think that sensor may be going bad? comments?

 

Here is monitor information

Anyone know what the oxygen sensor monitoring does ? Could it detect what is happening?

 

So I will swap the two lower O2 sensors and see if it is truly the sensor.
I reviewed all the posts on how to remove the sensors. I could not do it until I just used a pickle bar against the 22mm crowfoot and wacked the pickle bar with a 5 lb sledge.

Now where do those connectors go to? anyone?

 

The mount bracket is on the top of the gearbox just aft of the bellhousing.

The connectors are square Grey (S1) and Black (S2).

Sometimes the connectors are 'dangling' and NOT put back on the mount bracket.

 

From memory, the "secret" for the early car is that the lower O2 sensors can be reached through the A/C drain plugs in the foot wells. I have a later car, and getting the lower sensor out meant taking the cat out (no enough room to swing the breaker bar. There was no checking/swapping sensors for me, too much work. I just changed it.

Best of luck, keep us posted.

 

I replaced all 4 O2 sensors and within two drive cycles the cat monitor was okay, and the car passed smog. 115K miles.

 

Well done....