O2 sensor fluctuating

So im new to tuning and i was doing data logging and i noticed the o2 sensor at idle and cruising it drops to 0mv on a regular basis. It goes from around 900mv down to 0mv back up is that normal?

it's totally normal. basically, an o2 sensor just reads 'rich' or 'lean'. it never truly indicates how rich, or how lean, except in a very narrow (and totally unreachable) 'narrow band'. that's why it's called a narrowband o2 sensor.

around 500mv somewhere is 'perfect' (stoich or 14.7:1 on gasoline) but it's impossible to actually reach it for any period of time, so the ecm in a proper state just tries to get to a point where it can switch between rich and lean as many times per second as possible, to reach 500mv AVERAGE.

depending on how other closed loop systems such as BLM and INT are working, the switching might be super fast and never hang, or it might have sloppy moments where it sticks at 0v or 1v for a bit. that's also normal.

I've found that under normal cruise conditions if O@ voltage hangs on one side of stoich and/or the other for a while that it's due to a bad or failing O2 sensor. Under transitional periods, or WOT then yes staying at one extreme or the other is normal.

Ok cool. Thank you guys for the quick replies. I have another question about emulating with the APU1 from moates i get a code 51 every time. It idles for a second then CEL flashes and the motor sputters almost dies then the CEL turns off and it idles for a few seconds and does it again. Im using the Autoprom from moates and TunerPro RT and followed the directions for emulating and no luck. My eeprom chip tune works fine just not the emulation

Are you setting the mask ID to AA in the bin you are using to emulate with?

Not sure what that means so no i am not haha

Here is a screenshot of what you change in $0D mask for emulation. Other masks are similar. Screenshot is from TunerPro.

Would it be the same for $8D?

Edit: I can only find the prom id no mask id in my files unless Chip Code Mask is the same? mine says 8D Hex at the moment

I'll load up an 8D bin and get a screenshot of it

Here is what $8D looks like with the XDF I use. Change the 8D to AA and save the bin to the APU1.

You use the exact same xdf as me. Alright sounds good is there anything else i should know about emulating and logging?

Try one thing at a time. Make one change at a time when tuning and check the results. Otherwise you may help one problem and cause another. Make some logs and notes on what drivabilty issues etc you have. Take it one step at a time.