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01 XJ w/1 O2 sensor!?!?!?

K

krakhedd

NAXJA Forum User
Location
Buffalo, NY
Ok, it seems very fluky, so I have to ask. I *SHOULD*, according to many posts I've read, have 2 O2 sensors - 1 pre-cat, and 1 post-cat. I know what they look like, and have looked several times, thinking I overlooked something prior, but have still only found the one stuck in the header.

Why do I have only 1 O2 sensor? Is is the state that the Jeep was delivered to? It doesn't make sense, and I don't have a trouble code popping up that it's missing, either.

Thanks guys!
 
With a 2001 (4 litre engine) you should have 4 oxygen sensors, due to the split exhaust manifold design. If stock, you have a single header for the front three cylinders, and another for the rear three cylinders. It works like this, for each three cylinders: manifold, upstream oxygen sensor, precat, downstream oxygen sensor, then the two pipes come together into a single exhaust pipe and go to the full-size cat. I just confirmed this on my 2001, in my garage.
Now I'm not exactly impressed with this design. Another case of bless the Chrysler engineers with a brick. I have no intention of endlessly replacing oxygen sensors. I wonder if I could put on a header and use one upstream sensor spliced to both circuits, and one downstream header- anybody done this?
 
I can tell you that wouldn't work. Simple electronics. You'd double the resistance, which I think halves the voltage......anyway I'm not sure of specifics, but you'd have to splice in another resistor. Ask Dino Savaa about it, he's a whiz with that stuff.

Anyway, I am going to check this out later on tonight/tomorrow. I know I have 2 separate headers, collected into 1 (thinking about getting true duals......it would be f****** PHAT - "but I digress") . The only place I've ever seen an O2 is in the cylinder #4 header, near the collector, but I haven't really looked between that one and the exhaust ports. I assumed there would not be one, much less 3 more.

I guess the thing that amazed me is that I don't have a post-cat O2 sensor? My 99 did, but not this one.
 
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1.) Ohms law works out differently when the resisors are in parallel rather than series.
2.) Lambda curve oxygen sensors aren't resistors (on most models). It is a type of battery a small voltage when it gets hot and there is a difference in O2 content between one side and the other side of the sensor. Renix XJs did use a resistor type sensor but ChryCos should have 4 wires, the battery + its - and a 12v circuit that heats the sensor on startup.

Possible problems include: the O2 sensor not making enough amps to satisfy the 2 computer inputs even if voltage is equal and or the computer controlled heater circuits bieng spliced together or throwing codes if left open all together. (not quite sure about this)

So my conclusion is that it doable or at least try it unless anybody comes up with another objection.

There are eliminator circuits for second oxygen sensors. What is their point anyway?

Edit: krackhead are you sure you don't have an export XJ, ECU or aftermarket exhaust?
 
00-01 XJs will have either 3 or 4 o2 sensors. If federal specs it will have one cat (in the usual place) and 3 o2 sensors. Two at the manifolds, and one after the cat. If cali spec it with have 4 sensors and 3 cats. One cat in teh usual place and two coming off the manifolds. 2 O2 sensors before the cats and two after.

-Chris
 
I checked it out yesterday, looks like I've got 4 of them total. I wondered why there was additional heat shielding on the headers - I guess these are the pre-cats? WTF.......as if having 1 isn't bad enough, now I've gotta have 3........
 
If I replace them with real headers, won't that affect the readings coming out of the post-cat O2 sensors? IE, the O2 sensors mounted near the header collector.

Do you feel you would lose too much low-end tq to go with duals, or just not of interest to you to do so, or whatever? Are those custom-fabbed headers???
 
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The downstrean O2 sensors, from my understanding don't really "do anything" they just throw codes if they sense the exhaust coming from those cats (or pre cats I guess) isin't as it should be. So, I guess they (downstream sensors)could be relocated to after cat or eliminated using a downstream O2 sensor simulator which I think I mentioned. It looks like he included bungs into the header for the 2 upstream sensors. Those are avaliable on summiracing.com and I believe elsewhere (for less). Basically, the simulator is just provides voltage thats in spec with what the computer wants to hear, in a similar way that the MAP sensor adjuster does and you could probably build one using the same type of circuit if you knew what youre doing.

Look at those fugly things good I haven't seen them up close like in that pic, if you live here in CA buy your cars in Arizona or Oregon. Header looks nice though.
 
Duals? Doesn't do anything for the 4.0 and it would be difficult to route and not worth the cost.. plus it would look dumb... anyting less than a V8 has no need for duals. I especially like the 2.0L 4 cylinders with duals.. thats cute.

Those down stream O2 sensors (post-pre-cats) do nothing but tell the copmuter that the cats are there and working. You can either relocate both sensors to after the third cat (may not work) or get some sims to replace them.

The header is a Doug Thorley, but I had the O2 bungs welded in. Most exhaust shops have the O2 bungs to weld in. The particular place I put them on the header has more than ample room to put the sensors there.

I don't live in Cali, and the Jeep was never in Cali. It was orginally sold in NJ, so I don't know what was the deciding factor which got the federal and which got the Cali package. Although I think 00 was a transition year, as all 01s i have seen have the 3 cats. The O2 sims were about $60 each. I had tried to use a cheaper one ($25) but it didn't work and at that point I didn't have time to fool with teh company to get another one to see if it works.

-Chris
 
bajacalal said:
BTW by fugly I meant the 2 bulbous things on the old manifold not the bungs on the new header.
Click to expand...

Yeah I know that. Hopefully I can unload that POS on ebay. The bungs aren't attractive either, but are pretty necessary.
 
Pretty much all an O2 sim would have to do is put a constant 1.0V to the computer, right? That's easy enough to do......I may not have time until summer.....not like I'll have money til then anyway!

Duals on the 4.0 would look freaking awesome, at least IMO, also would be a little hard to route and might have to put some add'l heat shielding on the gas tank, but basically it would just be a mirror image of the factory location. I don't know if it would do much for a stock 4.0 - probably lose some low end - but I want to build a turbo'd stroker eventually, and dammit, it would just look cool! I hate to sound like a style-before-substance kind of person, which I'm not, but sheez, duals on a Jeep....who'd have thunk it? Who has ever seen true duals on a 4.0?
 
krakhedd said:
Pretty much all an O2 sim would have to do is put a constant 1.0V to the computer, right? That's easy enough to do......I may not have time until summer.....not like I'll have money til then anyway!
Click to expand...

Nope, that is not all it does.


As for the duals, it would look stupid if you put small enough pipe to stop a loss of low end torque. I.e. if done properly it would look dumb.

-Chris
 
Yeah it would. I'd probably go with dual 2.5"s - I don't have big enough tires to need to worry about low end at this point anyway. Plus, there's always the 2.72:1 reduction or whatever it is for the low range, in case I really need the torque back!
 
Cuz I'm going to eat them alive with a lifted Cherokee sitting on 33s with a turbo'd stroker, eventually! Again, I really am not concerned with the loss of backpressure (read my last post). I already have a Borla cat-back, and my cat housing is hollow anyway. Driving my Jeep back-to-back against my brother's stock 99, he has a little more tq off the line, but as soon as I hit 2500 revs (still fairly low), I am making WAY more.

Anyway, this is getting off the original topic, and I am done with the thread - thanks for helping me through my laziness in actually looking at what I've got hooked up to this thing guys! (I'm glad I asked, cuz I may never have realized I have 2 pre-cats I now have to get rid of.......)
 
Ok, ok, youre done but I have further questions for Talyn.

1.) Why did you not have the sensor bungs put in the downpipe (like earlier cherokees) right after the header was there something like not enough clearance or not enough wire?

2.) Any ideas what else does an o2 sensor simulator need do (the downstream one not upstream) besides provide a steady voltage in spec with what the computer expects?

thanks
 
1) I placed them there because the front up stream was monitoring cylinder 1, 2, 3 and the rear up stream o2 sensor was monitoring cylinder 4, 5, 6. I'm not sure if the computer actually gives diiferent fuel trim to those two sets of monitored cylinders, but I don't see why it wouldn't. So I duplicated the lay out on the header.

2) As for the sim, http://www.mr2.com/TEXT/O2_Sensor.html has a section on how O2 sensors work. Basically it alternates between a voltage. The O2 sims do not need to cost $60 each. I had one from here which I was testing prior to the need for a header: http://www.o2simulator.com which was a dual output, which simed two sensors for all of $30. The thing is that it worked great for 123 miles, but it crapped out after that. I checked all my wiring and such, but I didn't have time to 1) try some suggestions from the company or 2) get another one from the same company to see if I had a faulty one. It would have been a great deal if it worked, and I have heard that they work on XJs. However, I needed a good solution then and there.

-Chris
 
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