Passed the smog test...barely

[sgtsandman]

My understanding of the system is that it is comparative. The system looks at what is going into the catalytic converter and what is coming out of it. So both perform a function.

A higher octane does help to a point in some situations but is a band aid and costs you more money in the long run than addressing the real issue or issues.

 

[RonD]

O2 sensor's generate their own voltage by a chemical reaction with Oxygen
0.1volt is High Oxygen
0.9volt is Low Oxygen

O2s are also Heated, so have a 12volt and ground wire, those are the 4 wires
O2s can't work until heated above 600degF

Upstream O2's(closer to engine) are the main feedback sensors for the computers "on the fly" STFT, Short Term Fuel Trims, in fact the ONLY feedback, so if they are off/old then computer will be off, there is no backup sensors for these
Computer tries to keep upstream O2 voltage at 0.4volt, by varying the Open Time of the injectors

Downstream O2s(after Cat Converters) check if the Cats are burning up the extra Oxygen in the exhaust, which they will if they are working
Computer tries to keep Downstream O2s at 0.8volt

If an O2 starts to run out of the chemical, voltage goes down
On upstream O2s this causes a FALSE LEAN, so computer will run the engine Richer than needed costing you MONEY in wasted fuel, also false lean codes if old O2s are left in too long

On downstream O2s, a similar thing, Cat Converters are heated up by unburned fuel in the exhaust, ain't much but there will always be some otherwise engine would overheat from running TOO LEAN
If downstream O2 is running out of the chemical then it drops to 0.7volt and Computer starts running the engine RICHER to try and get the Cats Hotter so they can stay working, and this is also costing you money in wasted fuel
Downstream O2 showing lower than 0.8volt ALSO causes Long Term Fuel Trims(LTFT) to go up
LTFT is saved in computer memory so computer doesn't have to re-learn the engine system on each start up
So it "remembers" the lower voltage in the downstream O2 and runs engine Richer on start up

Change ALL the O2s, 12 years or 100k miles, for best gas mileage and no False codes
And just FYI, by the time a worn out O2 will set a code, you could have bought 10 or more new O2s with the money you have wasted on fuel

 

[racsan]

A year ago I put in a new O2 sensor when I replaced the complete exhaust system, manifold to final pipe and Ive noticed quite a difference in fuel useage. Its quieter too, which Ive finally gotten used to. As far as I know it had the factory original sensor in it, I wasn’t about to try & remove it although the sensor in my replacement fleabay manifold came out ok.

 

[scotts90ranger]

If I remember right a '92 should only have pre cat O2 sensors but it likely has two of those on a V6, one per bank of cylinders

Higher octane makes the fuel burn slower which makes it burn a little cooler which as explained earlier could lower the NOx output

 

[rubydist]

Correct, 2 oxy sensors, one for left bank and one for right bank, both before the cats.