johnlocke

I have an '01 XJ. I don't /believe/ I have california emissions on it.

What I /do/ have is four O2 sensors. To use the terminology that captainwoot gave me, 4 sensors: 1 upsteam for cyl 1-3 above the converter for those cylinders, 1 upstream for cyl 4-6 above its converter, 1 downstrean cyl 1-3 behind the converter but before the catalytic converter, 1 dowmstream cyl 4-6 also behind the converter but before the cat.

I got another O2 sensor code today after having replaced the lower two (downstream two O2 sensors), which fixed my first O2 code.

What I'm wondering, instead of replacing two more O2 sensors, I'd like to replace the headers anyway.

Can I switch to headers that /don't/ have converters and have either /two/ O2 sensors or one or none? Will I also have to re-chip the jeep?

The work to replace the headers back to the cat is pretty simple. I can do that part. It's the going from four O2 sensors to one or none that I don't know about.

Do the converters do anything meaningful? If so, why aren't they on so many other jeeps? If not, I'd love to remove them and streamline the output of the system.

Abovetimberline

If you have four you have ca emmisions,ca is the only state that requires it,if you want to remove sensors you would also need to have the pcm and harness for an xj that does not have four,you have to at least have the other two. Before you change anything I would check with the state you live in on there laws.

johnlocke

Ok, so I finally found another site
http://www.4x4xplor.com/O2-sensor.html

Definitely have four, so almost definitely (as you say) have California emissions on the 2001.

The next part you say, I don't quite understand. I /do/ get that I'd need a new pcm or reprogrammed chip and perhaps a different harness (might no need a different harness if the chip is reprogrammed to ignore some inputs), but I'm also not sure I'd still need /two/ O2 sensors.

For example, the '91 I've been working on with a buddy only has one O2 sensor. I wouldn't imagine that it's so different from the '01 that with a new chip two would be required. Mind ... I wouldn't be /against/ having two, but I wonder at the utility when the two O2 sensors on the systems I've seen have one on a single cylinder and the second on the full bank of that cylinder, and that's it.

As to the legality, yes, it'd be legal, and no, I'm not trying to get around various smog emissions. Smog testing isn't even required where I live (I think both Denver and Boulder require it, but not most of the rest of the state). I'm not going to remove the cat or the muffler or even go high flow on those. I'd just like to improve the headers, and it appears /much/ easier to do that without those mini-cats in there (read: much cheaper), and if they're not required in my state anyway, then why have extra crap to break.

Abovetimberline

The reason you need two is yours is obd2,91s are obd1,in 96 all cars had to be obd2 which means you have a sensor prior to the cat and one after. The one after checks cat efficency and will adjust the one in front which inturn will adjust injector pulse width. if both are not working right you can run rich which will destroy your cat very fast.

johnlocke

Ah, that makes sense.

So here's a /new/ part of the question, then. If I need a sensor both pre and post cat, does that mean to replace my O2 sensors in the /new/ headers (to get down to two O2 sensors and remove the mini-cats /in/ the header pipes), I'd have to install an O2 sensor behind the /actual/ cat, and then get headers that have the other O2 sensor just anywhere in front of the cat (for instance ... directly off one cylinder, vs off one bank, vs after all banks have been combined).

Any idea?

Abovetimberline

To switch over you would need the pcm,harness and exhaust system from a non ca xj for the year that is legal for yours. It is alot of work for very little or no gain.

COSXJFAN

I'd leave it alone. If it ain't broke...yada, yada

jeepxjho

The money needed to swap from CA emissions xj to a non CA xj would cost more money then it would if you replaced all the 02 sensor for the life of the xj.

I checked the local autozone for pices on there o2 sensor and its about $250 for all 4 so unless you can gather the header,exhaust system parts,pcm and harness from the junkyard its going to cost you alot more then just replacing them all a few times.