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Downstream o2 sensors
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shearinfinity Offline
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Post: #1
Downstream o2 sensors
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.

I have a digital quad efie, but before tuning, want to make sure all is right.
03-27-2012 10:07 PM
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shearinfinity Offline
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RE: Downstream o2 sensors
Yeah so after more specific searching, im reading this is normal for the sensor to float around. I somewhat knew it was used for cat efficiency, just not exactly how. So what i gather is if the cat is not hot enough, it reads low voltage to dump fuel to heat the cats? Is that why my fuel trims show positivie numbers on the downstreams? Then when cats are hot enough it shows the floating .8ish volts? Is there any way to steady this? Most the time fuel trims show +10to20ish on the down streams when driving/cruising. I havent checked voltage while driving yet (hard to reach) but for the main part been looking at fuel trims.

If i were to set analog efie to anything above like .120mv, when it jumps, it would hit near/over 1v. But for the most part i believe it sits at like .1v dumping in fuel(when left unmodded). Is it ok to have downstreams set higher at .3v with the chance of it jumping over 1v? Would throw a cel right or no?

Theory?
My engine does run really cool most the time (water/meth) which i believe is exhaust causing cats to be cooler than normal causing the .1v reading? Or would that not matter? Any thoughts, or suggestions?

Sorry for so much typing but thinking outloud heh. Been a long time forum browser, nearly done with project, just down to tuning for results.
03-27-2012 11:55 PM
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mike Offline
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RE: Downstream o2 sensors
You got me. You'll have to tell me about this one so I'll know. I'm not familiar with the situation. I can tell you that the downstream sensor always floats around like that, at least on a vehicle with a good cat. It floats kinda low, then goes up and floats higher for a while, etc. Its that behavior that made us not use digital EFIE on downstream sensors.

All I can tell you is you have to play with that downstream EFIE. Also, I can tell you that .2 or .25 is the more normal setting for downstream sensors. It doesn't hurt if the total voltage goes above 1.0 volts. Real sensors go over 1.1 volts. The computer doesn't detect how high the voltage goes. It only checks to see if its above or below .45 volts. It most definitely won't hurt anything if higher voltage is on that wire. I've put 5 volts on them before. Nothing will be harmed. It may throw a code, and not work well, but nothing will be harmed by it. Don't worry if you go over 1 volt.

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03-28-2012 03:52 PM
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shearinfinity Offline
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Post: #4
RE: Downstream o2 sensors
ahh very nice to know, this way I can at least push it above .45v I hope, it may have been a bit lower during reading if my HHO cell was on (cant remember exactly if it was or not).

I can't wait to get good results, I have a feeling my car may be a bit more difficult seeing how as I haven't seen 1 person use HHO with my car with electronics. Actually most nissan/infiniti forums laugh at the idea. I aim to prove them all wrong lol.
03-28-2012 09:56 PM
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mike Offline
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RE: Downstream o2 sensors
You should do fine. They're laughing only because they don't know what hydrogen does. There's no reason you can't get good gains on an Infinity.

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03-30-2012 02:47 PM
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