06MonteSS

when reading/logging the stock O2's, which one would give you a higher reading - the sensor before the cat, or the one after it??

edcmat-l1

iTrader: (10)

What do you mean by higher? They act differently. The upstream 02s oscillate rapidly from lean to rich, while the downstream ones when warm tend to stay around .600-.700v at cruise. Upon decel, the downstream 02s will drop to around .100v. Whats happening is the cats are storing oxygen during cruising, the reason they are at .6-.7. And then on decel they release a bunch (of oxygen) so the voltage drops as in a lean condition. Remember, the downstreams DO NOT report MIXTURE only the presence of oxygen. Higher voltage, low oxygen content, low voltage, high oxygen.
Before the cats heat up and start working, the downstream 02s will mimic the upstream 02s. This is also the case if the cats are hollowed out. This is how a an obd2 system can determine catalyst efficiency. I have some multi channel scope shots of upstream and downstream 02s together that will give you an idea of whats going on. PM me if you want or need them. I would try to figure out how to get them to you.

06MonteSS

higher - that's what I mean - LOL... I should have also had "..at WOT" in my original question...

when at WOT, which one would be reading higher, the one before the cat or the one after the cat??

I'm getting a log where one of them reads .860-.870 and the other one reads .890-.915... but I'm wondering if the log headings are reversed... cuz my AFR looks good (12.6-12.8), fuel trims zero out, etc etc, but the excel file log headings show O2 #1 at .866-.872, and O2 #2 at .890-.915.

last week, using my Predator, I upped the PE ranges to be +6% in both of them... then at WOT, the O2 #1 readings were still only at .870-.880...

The O2 #2 readings are always higher than the O2 #1... and it seems like the O2 #2 numbers are right where I want to be at...

so that's why I was asking which O2 gives the higher reading at WOT - the one before the cat, or the one after the cat?

Thanks for any and all info!!

jimmyblue

iTrader: (11)

B1S1 and B2S1 are before cat and B1S2, B2S2 are
after. Be sure which #1/#2 you're talking about.
And then, fuggedaboudit because you can't put a
good number to a NBO2 sensor in that region of
operation. It's more about heat than mixture at
that point and you don't know the temperature.

2001WS6Vert

Even though they are the same part they have different jobs. For tuning ignore the rear 02s. They are really just catalytic converter efficiency sensors. Their job is solely to monitor catalyst efficiency. The rears won't fluctuate any where near like the front because the gases have run through the cat. They will appear way more stable and centered (400-600mv) assuming you've got a good cat. If the cats start to die they will start to read like the front 02s and trip an efficiency code.

06MonteSS

yeah, I don't have 2 banks... just 1 - there's only 1 exhaust comin' out of these '06 Montes, til it splits with a y-pipe at the back for the dual ends.... with 1 O2 before the cat, and one after...

edcmat-l1

iTrader: (10)

As for tuning, ignore the downstreams completely. Now when you are logging, and you see discrepancies between the UPSTEAM 02s, depending on how much, that may be an issue. As was stated above, the rear 02s do nothing but monitor catalyst efficiency . They monitor oxygen content. As far as what they should show at WOT, they should be about 700mv plus. So it is possible for the rears to be pretty close to the fronts under WOT.

edcmat-l1

iTrader: (10)

Is that not a v6? Just looked at a wiring diag and looks like you're right. (I love ALLDATA)
AINT THAT SOME SHIZNIT. I would think like any other OBD2 Vee engine, it would have one upstream for each bank. Damn front wheel drives!! J/K,lol

06MonteSS

ok... the readings I'm getting must be correct then - cuz the O2 #1 is jumping all over the place, while the O2 #2 is pretty stable... so O2 Sensor 1 is the one before the cat...

thanks!

06MonteSS

no, it's not a V6... it's a 5.3L V8 LS4 - yes, fwd ;-) that's why there's only one/single exhaust pipe under there - hence only 1 front O2, 1 cat, and 1 rear O2... ;-) then in the back it splits with a y-pipe out to the 2 mufflers/tips...