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Bypass O2 Sensor

Fastdemise

NAXJA Forum User
Location
Beaverton, OR
I would like to play around with the idea of replacing my 0331 Head with a later model one. Was wondering if I could just still use 2 out of the 4 o2 sensors. Something like I just splice 2 into 1. Maybe could trick the computer into thinking it still has the pre cats since it will not notice a difference between the output of the o2 sensor and still be able to adjust the Air/fuel mix. Doing this should net me a few ponies and I still have my main cat so I can still be street legal and earth friendly. Yay/Nay?


I have a 2001 XJ Sport
 
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its a PITA. You can get an o2 simulator for the two upstream. The two downstream feed directly to the engine management system. Your engine will run without them, but poorly. The engine will have no way of analyzing the fuel mixture. The theory of combining two into one sounds like it may work.
 
Do the older style pre-99 exhaust manifolds have o2 sensors on them??
The other cool thing would be it leaves you with 2 spare 02 sensors. That's a good thing since they are so darn expensive.
 
Interesting idea.
Nobody here at NAXJA will ever promote anything that adversely effects the air we breath.
The Cherokee's I own are all either Renix era or '96 model year rigs. Neither of those have o2 sensors on the intake. The '96's have two, one off of the header and another after the cat, and they don't run worth a crap with a malfunctioning sensor.

Some of you late model guys will need to chime in here.
 
its a PITA. You can get an o2 simulator for the two upstream. The two downstream feed directly to the engine management system. Your engine will run without them, but poorly. The engine will have no way of analyzing the fuel mixture. The theory of combining two into one sounds like it may work.

No, the Up steam O2 sensors are the two that the PCM rely on for the AFR in closed loop. The down stream (after cat) are just there to check the condition of the precats. The engine will run fine with the down stream sensors sim'd out.

And the PCM will not like them being spliced together.

If you want to use an older head you could sim out the two after pre cat sensors, get a pre 00 header and have two o2 sensor bungs welded on to the header (must still have input from bank 1 &2 separately)..or I have heard that the 00-01 after market headers work on an older head, but have no verification of this.
 
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Hallo. You have to deal with 12 Volt which is going to the O2 sensor for the internal heating element and the voltage that is generate by the sensor (0-1 Volt) and is going to the ECU. That's why the Zirconium types do have 4 wires.
If there is a malfunction in this information to the ECU, the engine will run crappy or there is an enginelight on. :confused:

'92 XJ
 
Interesting idea.
Nobody here at NAXJA will ever promote anything that adversely effects the air we breath.
The Cherokee's I own are all either Renix era or '96 model year rigs. Neither of those have o2 sensors on the intake. The '96's have two, one off of the header and another after the cat, and they don't run worth a crap with a malfunctioning sensor.

Some of you late model guys will need to chime in here.

With all due respect, I don't think he was talking about completely gutting his main cat or doing anything to adversely affect the air or emissions (aka "PurpleCherokeeing your XJ"). He simply wants to use a different head, which means a different header, which means a different downpipe, all of which can lead into the larger cat that will still do its job (and a better one), just need to combine 2 upstream and 2 downstream O2 sensors into one upstream and one downstream. I have considered doing the same thing to my '00, but I'd hate to put in all that head/exhaust work to find out that the sensors get all screwed up....
 
Interesting idea.
Nobody here at NAXJA will ever promote anything that adversely effects the air we breath.


I personally do not recommend running cats. Although I would never say that on here.... oops....
 
With all due respect, I don't think he was talking about completely gutting his main cat or doing anything to adversely affect the air or emissions (aka "PurpleCherokeeing your XJ"). He simply wants to use a different head, which means a different header, which means a different downpipe, all of which can lead into the larger cat that will still do its job (and a better one), just need to combine 2 upstream and 2 downstream O2 sensors into one upstream and one downstream. I have considered doing the same thing to my '00, but I'd hate to put in all that head/exhaust work to find out that the sensors get all screwed up....

If you want to use an older head you could sim out the two after pre cat sensors, get a pre 00 header and have two o2 sensor bungs welded on to the header (must still have input from bank 1 &2 separately)..or I have heard that the 00-01 after market headers work on an older head, but have no verification of this.

That pretty much tells you how to make it work.

Two options:
1) 0630 or 7120 head, two O2 sims for the two down stream O2 sensors. One earlier header that has the 1,2,3 cylinders into one pipe and 4,5,6 cylinders into another pipe. two O2 sensor bungs. Have the O2 sensors bungs welded into the exhaust header at the junction of 1,2,3 cylinders and the other at the junction of 4, 5, 6 cylinders. Install the upsteams O2 sensors in these bungs. Install the O2 sims where the down stream O2 sensors use to be. Cut off the down pipe right after the precats and have an exhaust shop attach the remaining down pipe to the header.

2) Try an after market header for the 0331 head on a 0630 or 7120 head, which already has the spots for the O2 sensors and connects to the stock down pipe. Swap in the head, install the O2 sensors, install the header. I don't know if this route works 100% but I have heard on good authority that it does.
 
why cant you jut weld some bungs on all associated piping, and stick the sensors back in?
 
why cant you jut weld some bungs on all associated piping, and stick the sensors back in?

The two upstream cat sensors are on cylinders 1,2,3 and 4,5,6 I don't know what that would do to the AFR if they were placed in the same spot. I wouldn't want to find out either. If you want to relocat the down stream O2 sensors to after the main cat I don't see a problem with that except possibly at startup.
 
heh, didn't think about just installing all 4 sensors. Though I kinda like the idea of just installing 2 O2 bungs and keep the other sensors as backup if I went with the sim route.
 
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