HELP!! O2 Sensor bypass!

[240SX.SK]

I drive a '95 240 and I'm starting to do the exhaust. Ran into a little bit of a problem however when I went to get the cat cut out. First of all, i'm an idiot and thought there was only one, second I didn't think there was a rear O2 sensor after the first cat. So, I need to find some sort of bypass for this O2 sensor so that I can cut everything out. I live in Canada and we have no emissions laws! So, I have no need for the cat's. Does anybody know where I can get an O2 bypass/cheater so that I can get on with my exhaust mods. Please let me know of any solutions you guys can think of!!! Essentially I want header back to resonator then out to muffler but I don't think this will happen because of that sensor.....

[navysnail]

just unplug it and you should be fine. the only thing is that the ecu will say you have a bad cat, which you wont even have so just ignore it.

[240SX.SK]

If I just unplug it won't it cause more problems than just saying I have a bad cat? Like you can't just unplug an intake sensor and everything will be peechy keen, the engine won't run properly. And I'm sure if it was as simple as leaving it unplugged my guy at the muffler shop woulda said that, no??

[navysnail]

if i have my facts right, the first o2 sensor tells the engine if it is running rich or lean. the second just tells the computer the cat is working b/c there will be more o2 sensed by the first than the second. if the 2 readings are the same, then the comp. says bad cat.the guy at the muffler shop PROBOBLY doesn't have alot of experience with the sensors that feed data to the ecu, that would be an electricion or computer guy.

[240SX.SK]

Okay this sounds like it may work but, where or who would you recommend I go to in order to find out for sure if this is going to happen. I'm nervous about messing with the ecu and sensors so I want to make sure this is done properly. Have you done this already? Do you know someone who has done this?

[Darius]

Isn't there a way to jumper (or maybe disconnect) the sensor plug? I remember seeing this on a honda board a year ago when I owned an integra. I would imagine that if that second O2 sensor was not sending any voltage, the ECU would:

A) interpret it as being lean exhaust condition or B) interpret it as being a faulty sensor

"Under normal conditions, the rear heated o2 sensor is not used for engine control operations." (1997 240XS FSM) Whatever normal conditions are??

Either way I think you'll still get the Check Engine light to come on.

Someone has to be more knowledgeable on this than me...

[whoflungpoo]

The CEL will come on, but it won't adversly affect your driving. The second O2 is definitlely just there to tell if the cat is working properly.

the first O2 is the one that if faulty will make you run pig rich...

I believe you can buy a cheater for the second o2 sensor that tricks it into thinking there is a cat if you can't bear to have the CEL on.

[navysnail]

or you can just use a piece of black electrical tape, lol

[240SX.SK]

When I took out the resonator box on my intake last year, the CEL came on. All I did was unhook the battery and hook it back up and it reset and the CEL never came on, everything was good as far as the ECU was concerned. Maybe this would work for the sensor too? Take it out and then undo the battery? Would it reset it, maybe making the ECU think that everything was normal?? I can't imagine the second sensor haveing anything to do with the engine either but which cat will it detect? There's one before and one after it, so the cat after the sensor could be removed and nothing should change right? As long as that sensor isn't reading backpressure or anything it won'tt know the difference. Any arguements?

[DGA]

I had a '01 GTI that had two O2s. You could run a test pipe and the CEL would come on because of the missing cat. No loss in power just that little light shining from the center of the instrument cluster. I am not sure of what kind of value the ECU is looking for from the second O2. Some guys wired on certain resistors to the second O2, and got the light to go out. Check out forums at http://www.vwvortex.com if you are very curious about this.

[navysnail]

and btw i think there is only 1 cat, the other "cat" is just a pre-muffler to quiet it down.

[whoflungpoo]

It's definitely not a pre muffler, I looked straight into through mine on my 95 when i put my header on .... me thinks it's a fitment thing for when the added em in later on. My wifes had the 2nd cat on her 97.

[RoBS.]

First off...I was in the same boat with u..Nissan messed up bigtime and cut the 95 year model in half...Bosch made the sensors and no longer makes them..I made the same mistake and messed up my rear 02 sensor..But i just took it off and my engine light doesnt even come on..Its a Temp only one so it doesnt make a damn..Just take it out.

[RoBS.]

btw if u somehow broke the sensor or somthing or stripped it so it wont come out of the old exhaust..just go to an auto parts store and get a spark plug to fit in..its the exact same thread size and everything so itll work fine...Sensors suck..i hate them..

[240SX.SK]

Yeah I know it's definetly not a "pre-muffler". After the header, it goes, cat, sensor, cat, RESONATOR(for making it quieter) then muffler. I'm glad everyone pulled through for me here, it sounds like the second cat is coming off and maybe even the first cat, I'm gonna check once more at my Nissan Dealership and make sure, but thanks again to everyone!! It's been a big help, well from almost all of you!!

[navysnail]

o, i see now. sorry for the mis-understanding