so I have a WS mandrel y pipe, car sound high-flow cat, and mandrel b-pipe all from WS....anyway, my factory O2's all were running pretty well for being the originals (mind you I have 130K miles) when I got a muffler installed and wanted it aligned properly in the cutout of our bumpers...being a lazy guy for once, I took it to a recommended muffler shop near my house by a friend with a z....anyway, the driveway into the shop is a very steep grade of which I had to pull over to get into the shop (imagine a muffler shop having a really high grade slope/driveway into their garage area...how stupid is that?) anyway, on the way in, I heard a bad scrape...and thought nothing of it at the time...after the work was done, the mechanic who worked on it pulled it out onto the street for me, again I heard the scrape (i am lowered on eibachs right now)...once again I thought nothing of it...so with my pda auterra obdII software, I checked my O2's graphs a week later for fun to see if I was running lean or rich and sure enough, my rear O2 sensor (ie. the cat sensor) was completely dead...took it to another shop, had all my O2's replaced with bosch and the front two are fine...the rear one in the cat was killed by the scrapping incident courtesy of the O2 bung on the carsound cat being at an angle towards the ground...anyway, is the rear (cat) O2 sensor on our cars supposed to look just like the graph of our front O2's...cause the shop reassured me it's fine, whereas...on the graph and testing the resistance, the O2 measures minimum voltage for 30 seconds, then it switches to maximum (completely rich) for 30 seconds....almost regardless of how I am driving....

my questions to you guys are:
1. how is the rear O2 supposed to act? (should it be alternating very rapid like the front O2's)?
2. how is the rear O2 effecting performance?
3. has anyone else experienced this with brand new bosch O2's?
4. does the rear O2 greatly affect emmissions?
5. could it be the cat that is bad or just the O2?

 

1. The rea O2s should act the same way as the fronts in an OBD2 environment.
2. The rear O2's do not affect performance in any way, shape or form.
3. No
4. They don't affect emmisions as in make changes to your fuel mixture and such, but if they're acting fishy they might flag at emmisions. (They are there to make sure the cat is doing it's job).
5. Swap the front and rear O2 (use an extension) and see if the issue follows the o2 sensor.

Disclaimer: The above info is pertaining to what I know about OBD2 on my 99TA, but the idea is the same.

You could always just take your cat off, swap your rear o2 sensor with an o2 sim and gain a few hp.

 

what is an O2 sim....how does it properly simulate the correct resistance?

so only fronts change the A/F eh?

where do I get or an O2 sim? and if the rear O2 doesn't affect performance, than why would an O2 sim gain me some HP?

 

The o2 sim does not give any hp per se, it only allows you to toss your catalytic convertor without having to worry about thrown codes. No cat= more hp.(Off road use only, of course )

Here are some examples of o2 simms. I would check Jegs first to see if they have one for your application. Otherwise, if you have the square OBD2 connector on your sensor, then a GM one might work, which can be found on th TByrne site halfway down the page.

EDIT: The emmisions test stuff only applies to an OBD2 equipped vehicle, OBD1 equipped vehicles are usually "sniffer tested".

http://www.jegs.com/photos/182104033.jpg

http://www.jegs.com/cgi-bin/ncommerc...28&prmenbr=361

http://www.kteller.com/store/product...roducts_id=208

http://www.tbyrnemotorsports.com/ls1catalog.html

 

This is assuming your oxygen sensors and catalytic convertor is working, the vehicle is warmed up and you are off idle. The front 2 sensors will be switching from 0-1 volts - going from at least .2 to .8 volts regularly. The rear sensor will be different because the cat is changing the amount of oxygen. 02 is chaning into co2. At steady throttle, the rear reading should be steady lower than .4 volts.

The rear sensor will not affect performance or emissions. Its signal is only for the ecu to test the cat. I'd only worry about it if it is causing your mil to come on, since you can't pass the smog check with it on.

 

so the rear 02's voltage on a graph per say should hold steady as lean when I hold the rpm's at say 2K rpm? around .4 volts or less? mine is alternating between minimum voltage and maximum voltage every 30 seconds....does this mean there is something screwy with the carsound cat I have? what if I have a tiny tiny exhaust leak about 2-4 inches back from the cat? would that change the cat O2 reading or would it not because the leak is rear of the cat?

 

bump bump bump bump

 

Looks like your cat is going to the crapper. I'n not a fan of the high flow cats after my own experience with a rt and others on the forum. Your exhaust leak shouldn't change the readings. It's small and behind the sensor. Just remember to change the cat before you do your smog inspection.