Upstream O2 Sensor Test Confusion... Please Help!
 

First post. Been a lurker for a long time.
I am trying to determine if my upstream O2 sensor is beginning to go bad. I use the Torque App with a generic OBDII bluetooth scanner. It shows the voltage of the upstream sensor. I think it shows 4 frames per second, so I assume it refreshes at about .25 seconds.
Anyway, the voltage is not a nice, consistent variance between +/-.1v and +/-.9v, which I would expect. The readings I get make no sense. Sometimes it reads .2v and sometimes it goes up and down like it should. However, it never gets above .7v.
I tried injecting propane into a vacuum hose to simulate a rich condition (off brake booster). The sensor would spike at .9v everytime, but not stay at .9v, no matter how long I injected the propane.
Do these results condemn the sensor? Any other ideas of tests I can run?
BTW, the truck is a 1999 Ram 5.9L with 161K miles. It has the original cat but these are not original O2 sensors. Kegger modded, throttle body ported, Hughes plenum gasket kit, otherwise stock.
TIA for any help!

Well, that sounds just like an O2 sensor is supposed to operate. When it slows down the changing voltage or not at all then it is time to replace it. My '99 V10 still has all of the oxy sensors still operating. I check mine with a digital volt meter.

Sounds like it is working as advertised. The the sensor sees the rich condition, the pcm will pull fuel. You should be seeing short term fuel trims going down at the same time. However, if you have over 100K miles on it, probably time for a new one. NGK or Denso please, skip the bosch. Our trucks don't like 'em.

Part number
 

Does anyone have a part number for the NGK or Denso upstream O2? I have a new Bosch in but I suspect this is part of the issue. I've rebuilt most of the truck and this is the only code I'm getting now which is affecting a few other things.
1999 2500, manual trans, 5.9 gas, 4wd. Even the dealer is confused. I've ben lurking the forums for a few months and you all are very helpful so far.

Advance auto has this one.

that one seems to have worked. Put it in tonight. Thanks again

Wow, that was quick..... Did you just go get one?

I did. Welded the y pipe into the new cat to make sure no leaks and ran to advance to pick this one up. Nobody could tell for sure if this was the right one and even the dealer was confused.