PumpinIron

I have a 2001 Cherokee and I recently purchased a set of Banks Torque Tube headers. In the process of installing them I plan on replacing all 4 oxygen sensors on the car as well as replacing the pre-cats in the stock down pipe. I don't have any error codes but the car has 131k on the stock cats so I figure that they're due to be changed anyways. Besides that, I just replaced the entire exhaust system with an aftermarket one so the rest of the exhaust system ought to be updated as well.

I had planned on purchasing the Walker pre-cats / down pipe that is sold on Amazon and at most auto part stores here...


However, upon reading more about that part it seems that it's a genuine piece of crap. The welds are horrible, the O2 sensor holes are not aligned correctly, etc. (just read the review on that page and you'll see).

Anyways, it looks like my options are limited so I'm curious to see what other people who own a 2000-2001 Cherokee have done to replace the pre-cats.

To top this all off, I'm confused as to why the 00-01 Cherokees even had these pre-cats to begin with. I mean I've already got a cat downstream before the muffler so why on earth do I need the ones in the down pipe?

I really wish I could just get rid of the cats in the down pipe and keep the one before the muffler...

extrashaky

I doubt I would bother replacing the stock downpipe if there's nothing wrong with it, but if you're hell bent on it anyway, Magnaflow makes a direct bolt-in replacement:

http://www.magnaflow.com/02catalytic...rectfit=447190



I doubt you're going to find anything better than that.

I believe all the 2001s had the precats, but not all 2000s did. Chrysler did some weird things between '99 and '01 while they tried to work out their emissions system. My understanding is that there were actually three different versions of the 4.0L exhaust in 2000. I have a 49-state version, and my downpipe has no cats in it:



That's right before I had it ceramic coated to match my Torque Tubes. I have a single upstream O2 sensor in the crossover pipe just after the downpipe and a single downstream sensor after the cat. It would **** me off to have four O2 sensors.

PumpinIron

Pretty sure we are already environmental terrorists to some degree for driving gas guzzling jeeps to begin with, ha ha!

On a more serious note the law says something like you aren't allowed to mess with the emissions system (including the cats) on any car that is 8 years old or less or has 80k miles or less.

Where I live in Oregon emissions is a cake walk. All they do is plug in an OBDII scanner and make sure all your systems are good. If they are and there is no check engine light then you pass. No tailpipe sniffer or visual inspections here in Oregon.

Considering that I already have a new catalytic convertor before the muffler under the car I had thought about removing the pre-cats and using that down pipe shown in your picture. Of course then I have the issue of whether or not that's going to make me throw a CEL or not.

I have the Banks torque tube headers and they have 2 holes for the 02 sensors so I am pretty sure I would be able to keep the 02 sensors in place.

This is just one big confusion to me. I mean why in the hell can't I just switch to the setup like they had on the 99 or early 00 models that have no pre cats in the downpipe? I guess those cars must have had different computers that didn't account for the extra O2 sensors or something?

Wish I knew what the hell Jeep was thinking with these damn 01 emissions. 4 O2 sensors and 3 cats... Give me a break.

extrashaky

Edit: Removed my illegal comments.

Once you do all this and get it back on the road, be prepared for all those O2 sensors to fail and have to be replaced. They may not, but headers often foul your sensors as they're breaking in, especially if you have them ceramic coated. Both of mine died almost immediately. I ran it for a couple hundred miles before replacing them to give the header a chance to burn off whatever knocked them out.

PumpinIron

I've had my banks headers ceramic coated so I intend on leaving the existing O2 sensors in there for a while and letting them go bad. At that point I will put in the new O2 sensors.

I believe I have 5 sensors then since there's 2 in the header itself, 2 after the pre cats, and then one before the final cat on the underside of the car.

I've been thinking... Couldn't I just find an ECU from a 99 XJ or something and then swap that ECU for mine? Then I could get rid of the two O2 sensors after the pre cats by just leaving them unplugged. I mean the only thing that could possibly be able to know that the extra sensors are missing is the ECU, don't you think?

Those magnaflow cats look nice but damn they are spendy...

extrashaky

Damn, you're right. I didn't look at the price on that. You could probably find a deal, but with a $700 starting point it would still hurt.

Swapping ECUs is beyond my experience, so I don't know what that would do. However, I'm pretty sure the '99 only has one upstream O2 sensor like my 2000. So then you'd have one too many.

Maybe you could just keep the existing downpipe after all? I think that's what I would do as long as they're still working.

GooseJeep

Hey, I actually just did mine. 2000 Jeep XJ California emissions. 2 Pre cats (monitored) and 1 after (unmonitored) I bought my pre-cats from

https://www.catalyticconvertersonlin...alifornia=True

These are by far the cheapest direct fit California emissions cats I've found. I spent a good month looking and they are great. Cleared my CEL and gave me a much needed MPG boost.

Good luck

Edit: There should only be 4 O2 sensors on CA emission vehicles. Get em from rock auto, NTK they are pretty great and come pre-anti cease greased.

md21722

My 01 has 4 O2 sensors - 2 before the pre-cats and 2 after; no O2 sensors on the downstream cat which is billed as "lifetime".

salad

That Magnaflow deal looks like a nice unit.

The mini converters in the manifold are much less complicated than the main cats and are less likely to clog up. If you're familiar with the light-off time of a cat in good shape you should be able to watch the O2S output with a live scanner and determine roughly what kind of health they're in. Honestly if your cats aren't clogged there's no reason to change them...

Other than performance of course!

Not sure where you heard the mileage/years thing. It's a federal law and applies to all vehicles since the law was introduced.

Well aside from it being illegal, yes the PCM on 4-sensor and 2-sensor models is different.

Well... they weren't, really. You can "blame" California. Well into the 4.0L's life CARB bumped up their emissions targets. In 2000 the XJ was available with two emissions systems: Federal and California. One met EPA and the other met CARB standards (duh). In 2001 it was harmonized into a 50-state model to simplify things. I'm not sure when NY adopted standards similar to CA but it's just easier to test and certify a single vehicle.

The 4.0L was their workhorse and they're not going to redesign an entire vehicle just because of some emissions standards. They did whatever they needed to do to ship units out the door.

As much as we love it, the 4.0L is a very dirty and inefficient engine. It was discontinued because it couldn't meet increasing economy and emissions targets.

You sure about that? The CARB-spec/50-state OBD-II PCM only has 4 O2 sensor inputs. Might want to crawl underneath and look! The rear cat is for aftertreatment only to meet tailpipe targets. In 2000+ XJs all O2 sensors - whether two or four - are actually used for setting fuel mixture.

Please read the website rules. The following stickies are at the top of the OEM Tech section:
https://www.cherokeeforum.com/f2/cat...er-laws-24337/
https://www.cherokeeforum.com/f2/ann...rum-com-rules/

extrashaky

Sorry, I missed that. I'll not do that again.

PumpinIron

Okay, okay.... No more talk about removing my pre-cats since I understand now it's 'illegal' and against forum rules. Maybe I'll just tinker with that idea on my own then since I'm pretty sure all I would need is the ECU from an earlier model without pre-cats.

You guys are right though, I do have 4 O2 sensors so I was wrong in thinking I had 5. Looks like two of them are in the header before the pre-cats and 2 are after the header.

I guess in my mind I didn't think I would be doing anything illegal since I'd just be changing my emission system to the one that was found on the 99 and 00 Cherokees which still uses a cat, just not as many.

Anyways, my intention when starting this thread was just to find out what other guys who have had to replace their pre-cats ended up doing. There's several aftermarket companies out there who make pre-cats, just don't know which ones fit right and aren't crappy quality like I have heard the Walker ones are.

Oh, and I figured replacing them would be a good idea because I've got terrible gas mileage (10 mpg or less in the city while driving under 2k rpms almost all the time) and I have a feeling it's a combination of O2 sensors / cats.

GooseJeep

I was in your boat, 10-11MPG combined due to bad pre cats and 02 Sensors. Replaced them with the one I linked for you, and I am at 16-17 combined. 3" Lift with 31" tires. Next up are my fuel injectors and spark plugs.

PumpinIron

Same issue I am having! Mine is a 4" lift with 31" tires. I know these things don't get great mileage but I am getting far worse than what I should be. The exhaust is brand new, cat is brand new, and now I'm left thinking that the culprits are likely the O2 sensors.

It makes sense to replace the pre-cats while I am in there only because you can get them for around $220 so you might as well. I mean mine have 131k on them, they are rusted beyond belief, and even though they probably still work fine it's not going to hurt to have new ones installed.

salad

The requirement is "as originally equipped", and the way of identifying this is through the factory build sheet attached to your VIN. To circumvent the law you'd need to change your VIN... which is a little bit more illegal lol

Yikes. I agree that is poor, even with 4" on 31s. Spark plugs fresh yes? Your year should be running NGK ZFR5N gapped at 0.035".

Times like these an OBD-II scanner with live data output helps a LOT. If you can borrow one I highly recommend it. ECT, IAT, MAP, TPS, and any of the four O2s could be causing problems. And exhaust leaks... dragging brakes... dry U joints... blah blah blah

PumpinIron

Haven't checked the spark plugs yet but I'm going to order some of those to make sure they're new anyways (the car is a new purchase so might as well replace them so at least I'll know when they were replaced last).

I just ordered all 4 O2 sensors from RockAuto which came to $131 out the door including shipping. That's actually not that bad for 4 O2 sensors. My old BMW M3 had 4 O2 sensors and each one was minimum $100 a pop.

I actually do have an OBD-II scanner with live data output. Call me crazy but I just don't know how to read / understand the live data. I can replace a motor myself, I just don't get the live data part of it and how to understand it.