Hi all,

I am hoping I can get some help with my Upstream O2 sensor. It is currently giving me a static reading of about 1 volt. When I rev the engine it drops a bit to ~0.9, spikes up to about 1.4, then levels out back to about 1. From what I know of most cars, this value should be constantly varying when at idle, like a wave sign.

History:
I've had some issues with my O2 sensors and cat in the past. I replaced my cat not long ago with a Magnaflow, and the downstream O2 sensor wasn't working. So I replaced that and it seems to be working fine now. But I still have that issue above with the Upstream.




Idle



After rev

Do I need to replace the upstream O2 sensor as well? Some other issue? Thanks.

 

The wave sign thing applies to a narrow-band sensor which is very imprecise. That's why it oscillates. The RX8 front sensor is a wide-band, it reads the actual AFR and there is no reason for that to oscillate.

1 on that scale is 1 lambda = 14.7 AFR

It drops to 0 after revving because no fuel is injected while the engine coasts down. All cars do this.

So this is all normal.

 

The upstream sensor is a wideband sensor. The current is measured not the voltage
It doesn't work the same way as a narrowband sensor

 

Keep an eye on that magnaflow cat, they tend to not live long attached to a rotary. You can monitor cat temperature via OBD if your downstream O2 is in working order.

 

That's great news! Thanks a ton guys!