Greetings all,

My o2 sensors bank1/2 sensors 2/4 show low voltage at idle. Doesnt really jump back and forth between .3 and .9 like the upstream sensors, itll sit very low at .05-0.15. is this a sign of old sensors that need replacing? They will jump in voltage if i rev, but its not a good pattern of back and forth switching, itll sometimes float at .8ish and slowly drop then go back down, sometimes switches for a bit, but overall not a good pattern.

No vacuum leak in engine bay, i going to check for exhaust leaks when i can. No engine codes. Idles smooth. This isnt normal though right? Mpg is maybe 20ish on very light driving, worse otherwise.

Some info:
2004 g35 coupe 140.000ish miles
Fuel trims show +10-20 most the time on those sensors bank 1/2 at sen2/4.
Fuel trims show +/- 8ish on bank 1/2 sensors 1/3.
Either short or long trims, rear o2s show a positive amount stated above roughly.

K/n filter and motordyne 5/16 spacer.

 

since its the downstream sensor the cats may be going bad, is it running rich?

 

Ah took another reading, O2's float around .2v or above to .8wish volts. I've researched its pretty normal for downstream sensors to act this way. But they arnt really supposed to switch back and forth like upstream sensors. Had me puzzled for awhile, but all seems good.