Touchy Subject...

[VanillaGorilla]

I realize the legalities involved and would never attempt this terrible feat...but hypothetically if one wanted to remove the Cat. converter on a '96 beast...with the O2 being behind it...how would one bypass or hack the computer into thinking the proper heat was being sent? -hypothetically ofcourse. Thanks to any replies. !!!1

 

[balloo93]

You could look into the MIL eleminators that a lot of the mustang guys run when they run offroad H or X pipes.

Not sure how they work, I assume they feed back the optimum readout to keep the O2 sensor feedback happy on the ECU.

Not that you ouwld do that kind of thing.

Something like this:
http://zx2racing.com/pages/articles/mileliminators.htm

 

[Love2Ride450]

Well, as long as your XJ is a trail only rig, it doesn't matter.:lecture:

It would only throw a code if the computer has a catalyst efficiency monitor. I am not familiar with the XJ ECM, but I put a header on a Neon once (for a customer, I wouldn't own one of those pos) and the header replaced the first cat. OE had a O2 pre and post cat. I drilled a hole in the exhaust pipe, welded a O2 bung in there and ran the O2's with only a 10" long piece of pipe between them and it never threw a code.

 

[Starboard M]

Well, as long as your XJ is a trail only rig, it doesn't matter.:lecture:

I believe technically to be in parks and forest service lands a cat is required.

 

[87manche]

I believe technically to be in parks and forest service lands a cat is required.

most likely, since most of those are considered federal roads.

 

[Love2Ride450]

That may be true, which is total BS, but do you need current registration to be on these trails? (Not roads) If you don't need registration, and this beast is a trailer queen, then you don't have to worry about inspections. No inspection=no need for cat. Hence the name "offroad pipes" for Mustangs.

 

[Wil Badger]

That may be true, which is total BS, but do you need current registration to be on these trails? (Not roads) If you don't need registration, and this beast is a trailer queen, then you don't have to worry about inspections. No inspection=no need for cat. Hence the name "offroad pipes" for Mustangs.

see here is Utah you have to register a trail rig like you would a quad.now that vehicle doesn't have to have a cat as far as i know once registered for off road only.it only has to pass a visual inspection for safety .

they make eliminator boxes that plug into the harness instead of the O2 sensor.now if they make one that will work on the Xj i don't know.

 

[Love2Ride450]

Here in OR, all you need to do is go to a Motorcycle shop that sells the OHV tags, give them a VIN and Year make model. They charge 10.50 and give you a OHV tag. NO inspection.
Anyway, try pulling the O2 out,(leave it plugged in) plug the hole and drive it. see what it does. The rear O2 generally doesn't affect fuel mixture much, so you shouldn't have any running problems, just watch for a MIL illumination. you will most likely have to go down the highway, because if it has a cat efficiency monitor, it will only run the test at cruise.

 

[MisterFubar]

The truck might throw a code but it will not effect how it drives or fuel economy at all. The downstream sensor is only there to monitor the efficiency of the CAT, it DOES NOT have any input on fuel or timing.

I drove with my downstream sensor disconnected for about a month and it never even threw a code.

 

[lancey3]

The truck might throw a code but it will not effect how it drives or fuel economy at all. The downstream sensor is only there to monitor the efficiency of the CAT, it DOES NOT have any input on fuel or timing.

I drove with my downstream sensor disconnected for about a month and it never even threw a code.

i think it will totally affect his mileage. the after cat sensor is there to make sure the precat one is doing its job, if it shows its not it might screw with the mixture.

 

[rmm727]

I'm not sure if this would work but what about disconnecting the plug from the o2 sensor and getting the vehicle up to operating temp then reading the resistance through the o2 sensor. Find a resistor of approximately the same value and put it in series with the plug (replacing the sensor for a resistor)

 

[Rev Den]

Why?

No benefit in pullng the cat....none.

Rev

 

[lancey3]

maybe if you were running a stroked and blown sbc it would help but on the 4.0 you won't notice any power increase.

 

[XJ Beater]

get a bung welded in, then get a pack of spark plug anti-foulers from the local autoparts store, drill one out with a 1/2 drillbit, screw it into the other one which you leave alone, o2 sensor screws into the drilled out one, small hole one screws into the o2 bung, essentially its a spacer for the o2 sensor, moves it out of the exhaust stream more=less crap it senses, makes it think all is well, worked for me, found it on a mazdaspeed sight or some crap

 

[Love2Ride450]

Why?

No benefit in pullng the cat....none.

Rev

Unless of course his cat is plugging up or plugged already.

 

[1996cc]

I believe technically to be in parks and forest service lands a cat is required.

No, they require a spark arrestor (i.e. muffler). Cats are actually hazardous off road - dry grass + HOT Cat = :flame::flame::flame:

 

[Love2Ride450]

i think it will totally affect his mileage. the after cat sensor is there to make sure the precat one is doing its job, if it shows its not it might screw with the mixture.

Not so much. As far as I know, the downstream sensor's purpose is to make sure the cat is doing it's job. If the upstream sensor isn't doing it's job, the ecm will "know" because the sensor will not react to changes in fuel trim.(mixture) The ECM will perform tests on the system while you are driving under low load conditions. One of the tests is to intentionally provide too much fuel to the system, and see that the O2 sensor "sees" the increase. Another one of these tests (that not all systems perform, not sure about the cherokee)is to monitor the readings from the pre (upstream) and post (downstream) O2's, and see that there is a drop from the front to back. This tells the ECM that the cat has a sufficient OSC (oxygen storage capacity) to perform it's job within specs. I have heard that the post cat O2 has some effect on fuel trim in some vehicles, but am not sure about that. The upstream O2, MAF/MAP, ECT and TPS have the greatest influences on fuel trim.

 

[hillbillyhell]

Not so much. As far as I know, the downstream sensor's purpose is to make sure the cat is doing it's job. If the upstream sensor isn't doing it's job, the ecm will "know" because the sensor will not react to changes in fuel trim.(mixture) The ECM will perform tests on the system while you are driving under low load conditions. One of the tests is to intentionally provide too much fuel to the system, and see that the O2 sensor "sees" the increase. Another one of these tests (that not all systems perform, not sure about the cherokee)is to monitor the readings from the pre (upstream) and post (downstream) O2's, and see that there is a drop from the front to back. This tells the ECM that the cat has a sufficient OSC (oxygen storage capacity) to perform it's job within specs. I have heard that the post cat O2 has some effect on fuel trim in some vehicles, but am not sure about that. The upstream O2, MAF/MAP, ECT and TPS have the greatest influences on fuel trim.

That is all correct. In addition, the downstream o2 sensor IS one of the inputs that determines long term adaptive fuel trims. The easiest way to describe a long term adaptive.....it's as close as the PCM can come to writing it's own program for your specific vehicle.

Unless you have a radical change in running condition that requires new adaptive maps, fuel mileage would never change noticeably with the downstream disabled.

All taht said, I'm still a pro cat guy.

 

[xjjeeper19]

The down strean 02 is responsible for catalyst efficiancy, and it is also responsible for long term fuel trim...long term is factored in during closed loop to help keep fuel trim in it's goal range.

 

[Love2Ride450]

The best way to monitor cat efficiency:

















Count the field mice left at the front door, and under the porch.
Sorry guys, couldn't resist.