Planning a complete exhaust system overhaul on a 2001... Time for... fun?

If I had to do it all over again, I'd buy a 1999 XJ for numerous reasons. Regardless, I have a 2001, and I love it, so I guess I'll just have to work with it.

I'm plotting out a complete exhaust system replacement for my XJ due to a muffler that's peeling like a banana, and the feeling that the rest of the exhaust system will be following suit over the next few years. Unfortunately it seems as though I cannot use APN headers due to the laws pertaining to tampering with emissions equipment, which makes this all SO much more fun.

So, a few questions:

1. My understanding is that in all 50 states, "crippling" a vehicle's emissions systems on a vehicle that sees street use is illegal. Is this the case? If it is not in the states of TX and NC, I'd like to scrap the god-forsaken pre-cats on my XJ in the hopes of eliminating the heat soak issue. In doing so, I assume I could use any aftermarket headers I want (such as APN) and trick the engine computer using Montana Fab's O2 sensor simulators. Would I be correct in assuming this?
2. Assuming what I've suggested in #1 would indeed be illegal, I assume I'd need to go with either OEM headers, or aftermarket headers designed for the 2000 and 2001 XJ's emissions systems (2 collectors with a hole in each for upstream O2 sensors). Is this correct? Edelbrock makes headers fitting this bill, however, I've heard mixed opinions on the quality and longevity of their Jeep products.
3. Provided my assumptions in #2 are correct, but I still decide to go with an aftermarket header setup designed for the 2000 and 2001 XJs, they *should* bolt straight onto OEM-style replacement pre-cats (and the corresponding collector/downpipe) - right?
4. Are there any performance gains to be had from an aftermarket downstream catalytic converter, or would it be best to stick with an OEM-style replacement? I'm planning on running a stock muffler - I want this thing to remain quiet (as it will be used for a hunting vehicle periodically).

My biggest concern is indeed #1, as I would like to get rid of my heat soak issue once and for all without throwing down on brand-new injectors and doing a full fuel system leakdown diagnostic... Ultimately I know it'd be the best option (as supposedly, if the fuel system maintains proper pressure, heat soak wouldn't be an issue), but money talks.

Please note that I do aim to stay in compliance with applicable emissions laws - please don't get your panties in a twist by me suggesting the use of O2 sensor simulators to eliminate my pre-cats.

Thanks in advance, guys!

I posted this vid up on a thread the other night, but here it is again. I did a full gibson exhaust on my 95 4.0l. Headers, and Catback. http://www.youtube.com/watch?v=GKVKvHHgUZE

I did notice a lot more low end out of the engine and imho I think my tone sounded much deeper and throatier than any Flowmaster, or Dynomax.

As for the pre cats I have no answers.

Thanks for the input - it does sound good, but I'm definitely wanting to keep my 4.0 as quiet as possible.

A little bird has informed me that the pre-2000 engine computer in conjunction with pre-2000 headers (i.e. no pre-cats) would remedy this issue without the need for O2 sensor simulators.

The question remains... Is anyone familiar enough with NC and TX emissions laws to say whether or not this is legal? I will be retaining the primary catalytic converter - just not the pre-cats. I know that they don't even perform visual inspections in either state - they just verify that the CEL light isn't on, and that the OBD2 read-outs are within spec, meaning it isn't a question of whether or not I can get away with it... I would just like to keep it legal.

I believe it would be illegal for you to do what you are saying, unfortunately. Frankly there is very little chance you would be *caught*, but it is not legal since you would effectively be making your emissions system that of a 99, and you are only legally allowed to swap newer systems into an older vehicle.

The little bird is correct. You could also put separate bungs for the upstream O2 sensors in the two runners for a 99-down manifold and mount the O2 sensors from below the precats behind the main catalytic along with the other one, or use simulators, but again, this would not be legal and you would be limited to off road use only.

For you legality question you are going to have to consult those states specific vehicle laws, meaning you will need to obtain a copy of them from each state. They can usually be found online (I just did a quick google search which brought me straight to the NC DOT site). However, federal law prohibits the removal of functioning O.E. cats. It also says that if a vehicle left the manufacturer with X number of cats than it has to remain on the road with the same X number of cats. They can be replaced with cats meeting epa certifications if they are found faulty, but you are not supposed to modify the number of cats found on a vehicle. Will you get in trouble in either state if you do remove the two pre-cats? I'd have to say no (since the only thing either state checks is on board diagnostics ie your CEL), but you would not be meeting federal emissions requirements since the vehicle does not have the same number of cats that it left the factory with.

southernrebel20 said:

For you legality question you are going to have to consult those states specific vehicle laws, meaning you will need to obtain a copy of them from each state.

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It's a federal law, not state specific. True, some states are more rigid than others but none are LESS rigid than the feds. The EPA is a federal agency...aka...Environmental Protection...:rtm:

Sad that you can't do whatever you want to do (well, you can, but it IS illegal) with your exhaust system but the regulation is there to keep the air cleaner.

Thanks for all the input guys, that's what I was afraid of.

On the note of southernrebel20's statement regarding the elimination of catalytic converters, I assume that's a federal mandate?

At this point, I wonder if it'd be worth considering relocating the pre-cats further downstream, out of the engine bay, to cut down on the heat soak issue. This would be far more likely to be legal, but I'm curious as to what other problems I'd encounter.

Did ALL later XJ's have the pre-cats? I know on the 3rd gen+ Dakota not ALL of them had pre-cats. So in that case you could technically remove the pre cats and still be legal?
If this is the case for the later XJ's then maybe good news?
Otherwise, for the rest.. Custom bent down pipe (get rid of that darn crease, lol), high flow cat, and either straight pipe as far back as you want or, muffler of your choice and custom bent pipe.

The reason for the pre-cats was startup emissions, when the XJ is running in open loop mode and the catalytic hasn't heated up enough to actually do its job. The pre-cats had to be put close enough to the cylinders that the exhaust gases were hot enough entering them to get the job done. Unfortunately that means moving them further down will make them useless... and is MAYBE illegal (I'm honestly not sure.)

Johnnie Walker said:

Did ALL later XJ's have the pre-cats? I know on the 3rd gen+ Dakota not ALL of them had pre-cats. So in that case you could technically remove the pre cats and still be legal?
If this is the case for the later XJ's then maybe good news?
Otherwise, for the rest.. Custom bent down pipe (get rid of that darn crease, lol), high flow cat, and either straight pipe as far back as you want or, muffler of your choice and custom bent pipe.

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From my understanding, all 2000+ XJs have pre-cats, which is why they're all prone to heat soak issues.

kastein said:

The reason for the pre-cats was startup emissions, when the XJ is running in open loop mode and the catalytic hasn't heated up enough to actually do its job. The pre-cats had to be put close enough to the cylinders that the exhaust gases were hot enough entering them to get the job done. Unfortunately that means moving them further down will make them useless... and is MAYBE illegal (I'm honestly not sure.)

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Definitely makes sense... It just makes me wonder how tuners are able to made such absurd modifications to vehicle exhaust systems whilst retaining street legality (then again, they may just also say "to hell with the law" and do it anyway). Depending on how lax the laws are, they may simply state what others have said previously (that the vehicle cannot have any fewer catalytic converters than it left the factory with) and not have any mandates pertaining to their efficacy.

I guess it might be wisest for me to start by just replacing my muffler (since it's peeling apart and has at least one visible hole in it) and go ahead and replace all my injectors, as well as the check valve in the fuel tank, to see if I can stop this heat soak issue. If that doesn't work, I'll go the fan timer route.

Another thought - as catalytic converters age and clog up, they tend to run hotter and hotter, right? Would it be worthwhile to consider simply replacing them to cut down on heat soak?

Honestly I would start with the fan timer route, and forget the rest if it solves the problem. Obviously the muffler needs replacing too.

If the cat clogs, it gets hotter, but if the catalysts age and become less effective, it gets colder because it isn't catalytically burning the excess fuel anymore.

For that heat soak. Just wrap injector 3 with aluminum sleeve and zip tie it on.
I added 2 layers for overkill.
I did this to my 00, and it never gave me that hot-restart shaky routine again. Sometimes wrapping #4 injector is necessary.
This thermotec stuff can be had anywhere, and its actually better than the stuff recommended in the TSB for heat soak issues.



The "debris shield" insulator placed across the intake manifold is not enough, because a wash of hot air of the exhaust comes up between exhaust runners for 3 and 4.

ONLY the 00-01 XJs with the 50 state emissions package have the pre-CATs.

00-01s with the 49 state emissions package DON'T have the pre-CATs.

The reason 50 state emission package vehicles show up in places other than CA is simple--there weren't enough CA sales and those vehicles got "dumped" in other markets.

Joe, you're a godsend in this forum, and your technical expertise is second to none on the XJ, but I still feel compelled to bite the hand that feeds...

I've searched high and low for a non-50-state-legal exhaust manifold for 2000 and 2001 Cherokees and have come up empty handed. Even referencing the FSM for 2000 and 2001 models, I only see the pre-cat design manifold referenced.

I was under the impression that *all* 2000 and 2001 XJs had 50-state legal emissions systems.

Now, I very, VERY well could be wrong, but if you have some information I've overlooked, I'd absolutely love to read it.

I love you, man... I ain't tryin to disrespect you up in heeyah.

anthrax323 said:

I was under the impression that *all* 2000 and 2001 XJs had 50-state legal emissions systems.

Now, I very, VERY well could be wrong, but if you have some information I've overlooked, I'd absolutely love to read it.

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My memory of this could very well be wrong (and it's late, cold, and I'm tired so not going outside to check), but: under the hood of my 2000 the emissions label specifically states that the vehicle was built to Federal emissions spec. There are no precats, and to the best of my knowledge the system has never been altered. Both oxygen sensors and the one catalytic converter have been replaced as service items, but that's the extent of the changes. Even the muffler is still (as far as I can tell) OEM.

Let me know if there's anything specific you'd like me to look at, and I'll do what I can to answer questions.

My 2000 did not have the pre cats.

My current 2000 XJ is a 50 state emissions and doesn't have precats. I could try and snap some pics in the next day or so. The exhaust is a 2 piece manifold. Jeep was originally sold in Michigan. It does have the heat wrap insulation inbetween the intake runners.

Good info, thanks guys.

So it looks like the 2000's did indeed ship both with and without pre-cats (chasdb's testimony is confusing, as it would seem as though the 50-state emissions package would have mandated pre-cats).

Has anyone seen 2001 models without pre-cats? It would seem logical that all 2001's would have had the 50-state emissions package given that it was the final model year and they may have tried to streamline the production line for phasing out....

My '01 parts catalog shows the availability of a straight pipe assembly that replaces the pre-cats. However, it is marked as being intended for the euro market (which I assume was all diesel motors at that point?) and for countries in which leaded fuel was still in use - probably south america, I'm not sure where leaded fuel was still widely used in 01. The pre-cat downpipe is 50 state, there is no 49 state / federal emissions downpipe setup for the 01. The part numbers in question are 5210 1112AF (50 state, precats) and 5210 1193AH (euro & leaded fuel.) Interestingly, there is also a main catalytic converter replacement (no catalytic element at all) in the catalog, part number 5201 9500AD, listed as "resonator, exhaust, S/C NAB Leaded Fuel"* so it appears that in countries which used leaded fuel in 01 got absolutely no catalytics on XJs from the factory. Guess they figured the leaded fuel would destroy them too quickly for it to be worth installing them, and seriously, any country still using leaded fuel obviously really doesn't care about air quality anyways.

So no, there was no 49 state / federal / no pre-cats setup on 01s available as far as I can tell. This is all catalog research though, not actual physical evidence. I am sure exceptions exist, and someone probably has an '00 with 49 state that was built late in the year and titled as an '01 on hand to prove me wrong :roflmao:

* anyone know what S/C stands for, or have a good guess? NAB means leaded fuel, per the table at the top of the page in the catalog.

Well, I'm positive I've had 01s with no pre-CATs to work on--however, Kastein is right on the catalogs. :twak:

A large chocolate chip cookie goes to the first two people that post up photos of their emissions decals for an 01 with 49 state data and no pre-CATs installed--must include the build date with the photo! hoto: