Let us know your results if you do!

 

the key to that would be determining that the o2 sensor is bad, though not so much that it sets a code.. the real discovery is that the down wind sensors are actually in play as far as the trims are concerned.. possibly even igntion timing- though I didn't go into that at all..

my 'learnin about sensors today has led me to believe this about BOTH upwind and downwind sensors, and it may be of extreme value to share:

better keep the outside of the sensor uncovered and uncoated with debris such as road gunk, anti-freeze, oil, grease and the like..

both sensors work the same way: the bitter end of them (that sticks into the pipe) have the obvious inlet probe.. but there is another set of inlets on that thing.. the sensor works by comparing passing air interior to the pipe to air outside of the pipe and by measuring minute voltages in the space in between the inlets..

if the interior probe/inlets foul, there will be a drastic change in the differences- and a code will trip.. If there isn't a huge difference, no code will trip.. meaning, your interior inlets could be clogged, and your exterior inlets somewhat equally clogged, and the sensor doesn't have a chance to determine if it's working properly because the voltages are within acceptable parameters..

huh... maybe the post cat o2 sensor is doing the same thing the pre-cat sensor is doing, but comparing voltage differences between them to determine what's happening environmentally? THAT, just occurred to me.. by doing so, they could determine if one is bad or not..

but anyway- the point I was making, is that the post cat sensor is in play for engine trim.. I don't think there is any way around that now.

 

either OCD, or BORED.. or, both..

I gotta think the non-fouler thing through.. reason:

I know for a fact how the sensor works now.. not how it relates to the PCM and trim (yet), but how the sensor as a stand-alone device works..

the non-fouler basically restricts air to the interior vents/probe/little dang holes... it isn't pulling as much 'sample' on the interior as it is from the exterior vents.. since the interior probe/vents aren't sampling as much of the stream, and in direct comparison to the exterior vents which are disproportionately drawing more clean air since you blocked the interior vents- whah-lah- the air looks like it's been scrubbed by a catalytic converter.. test: if you were to block air passage on the exterior vents, like, with aluminum tape or something, you would lower the voltage compared to the interior vents.. in effect, cheating from the opposite direction, and in effect fooling the sensor into thinking the o2 counts are right, and it telling the PCM the same thing..

if my little theory works, wrapping something like aluminum tape on the outside of a sensor, and blocking the vents will do the same thing as a non-fouler.

 

With my setup I normally get between 12.5 - 13.5mpg depending on driving. One time I saw 14mpg, and I jumped up and down with joy ... well almost did.

Any chance doing live o2 data with LT/ST fuel trim data on my truck would aid in your adventure? I have the reader, and my rear o2 has a non fouler (different from typical install, I didn't double stack).

 

Ah the suspense was killing me. Not sure what I am looking for, but I grabbed a few pics after switching to CL. I will make a note that in the 2 pics that show stft for sensor 2, there wasn't always that big of a difference. Most times it hung around each other, sometimes with only a .02 difference. One thing I thought was interesting was my STFT for sensor 2 % was always 99.2%. Not sure what that means.

 

was the non-fouler in play or out?

the rear sensor held steady at 99.2%?

did you by chance throttle it to see if sensor2 held steady at higher than idle?

 

Non-fouler is always in because I get a cel with the highflow. Throttle does not change the % on sensor two, only the voltage. Actually, this could be correct if our original assumption that sensor 2 only checks for cat efficiency and isn't concerned with fuel trim right? Because it doesn't fluctuate, I think that is the value the computer is giving no matter what the sensor value is. Still doesn't answer your question about why mpg shot up though... Then again, I wish i knew what I was talking about :P

Edit, from what i looked online for bank 1 sensor 2, it seems others have a 99%

 

dude.. you know at least as much as I do.. most likely more.. I'm bumbling through the dark here..

my contention is this, fwiw: that sensor2 reading should alter, but it should stay in a steady relationship with the front one.. I'm thinking when that relationship breaks, and the rear sensor shows less deviation in o2 than the front one is when there is a problem, and a code is set.. I bet a dollar, so long as it doesn't close the gap in o2 content, no code is tripped.. meaning: a whole lot less o2 in the stream is okay- a comparable amount is NOT...

if you look close at your sensor, nearing the back of it (where the wires terminate) you'll see about 4~6 holes around the perimeter of the sensor.. since you have that non-fouler, and seem to want to play too- do me a favor just for craps and grins: remove the non-fouler, and aluminum tape around all but one or two of those vent holes so there is less 'fresh' air comparison for the sensor.. I bet you DON'T set a code.. I bet it brings the voltage difference between the two ends closer, and I bet that registers as more o2 in the stream.. in other words, you've done the same thing from the exterior of the sensor as you did to the interior of it with the non-fouler.

but anyway:

I pulled bank2's downwind o2.. I've only ran it for a few miles.. It closed loop w/o setting a code, but I didn't notice any funky readings.. the cross counts didn't change on that bank, and it still roughly matches bank1..

so, maybe the downwinds don't affect fuel trim.. but, maybe a CEL does- which plops the engine back to open loop no matter the environmental conditions.. I don't know yet.. I still can't explain the increase in economy and perceived power..