exhaust options for '01

other than being illegal (from what i can gather), is there any mechanical/electrical reason why i couldn't replace the exhaust, from the header all the way back to the tip, on my '01?

i think i may have the cracked manifold syndrome, but because of the emissions stuff (pre-cats) the local muffler shop won't touch it (now i know why all the application charts only go up to '99).

so *in theory* could i use an aftermarket header for a '99 if i installed it myself? while i'm at it i wouldn't mind getting a more svelte cat instead of this big cylindrical thing.

anyone w/ a 2001 done an exhaust swap?

thanks.

Ive got an '01 myself and will be going with an aftermarket exhaust soon. First off, I may be wrong, but the cracked manifold issue was supposed to be taken care of when the factory went with the dual outlet manifold. The idea being that the added heat from the exhaust of an MPI motor was being divided up into two pipes which would decrease the stress on the collectors. Not sure what year they went to a dual outlet manifold setup, I think '00. I would be surprised if you still got a collector flange crack with the dual outlet manifold, not that it couldnt happen though. Some of the other guys were saying that it IS illegal to remove a good working cat just to go with a high flow unit, but it may depend on your state. 'Random Technologies' makes high flow cats for all kinds of jeeps, check out their website. The only electrical 'issue' involved that I know of is the oxygen sensor, and that is not an "issue" at all,really, as all good aftermarket headers have a boss for it to be screwed into. If you were to remove the two precats and the pipe that leads to the main cat, and then tow it to an exhaust shop and just tell them to make a 'Y' pipe after the exhaust manifold which fed into a larger diameter pipe going to the main cat, I dont see why they wouldnt do it. Im thinking that if they arent the ones who removed the stuff, they might not care what gets put back in its place. Tricky subject here, I'll agree. Anybody with more or better info on this topic jump right in, as I will be in the same boat in about a month.

Me again, sorry for the thousand word responses, but I forgot to mention the header bit. Check out 'Clifford Performance' website. They have a neat dual outlet header for the '01 cherokees that comes in ceramic coated or stainless. Im probably going to get the stainless. It will NOT bolt up perfectly with the precats, but after talking with them several times about it, they damn right insist it will fit perfectly otherwise, and also has the boss for the oxygen sensor. An exhaust shop should be able to match up the precats, but then that takes away the advantage of going with the header, right......
I would just get whatever header you decided on, install it, remove the two precats, the headpipe and the main cat and put them somewhere (???), get a high flow cat from 'random tech', and take that and the xj down to the exhaust shop and tell them to connect the dots using a slightly larger dia. pipe than was originally there. If they ask what happened to the old stuff, just say you were thrashin the mean machine and some rocks ripped the stuff off and destroyed it. Then while you're at it, go the full mile and install a good cat back setup too! Why stop halfway, right?
Let me know what happens, Ill even pitch in for your bail....

Got some more fer 'ya to think over. 'Gibson' also has a nice stainless header you can use for the late year XJ's. They also have a good cat back system that will go well on that new main cat you're probably going to get.
BTW, this may be interesting to you as it was to me. I recently got an emissions check on my '01, and I noticed that they didnt do the 'ol tube to the exhaust pipe test! I asked the chick why and she said that on cars after a certain year (new cars I guess) they plug a hand held code reader type unit into the pigtail under your dash, and the automobiles PCM tells them if the emissions equipment is working or not! Too cool, huh. Soooo........being that the last wire in the emissions system is the one going to the oxygen sensor, it would seem to me that everything after the header is fair game as long as you can find an exhaust shop that will play ball! Because without any wires, the PCM isnt going to know!
(remember what I said about the bail........)

MMIXJ said:

other than being illegal (from what i can gather), is there any mechanical/electrical reason why i couldn't replace the exhaust, from the header all the way back to the tip, on my '01?

Click to expand...

I'm a new XJ owner, but can tell you this. If you remove the cat or cats, which ever you have, your OBDII will notice the change and trip the CE light. However, that being said, you may be able to purchase a device that tricks the second O2 sensor. caspers electronics has them for some cars.

However, you would probably be just as well off leaving the cats alone. I doubt you would gain any significant HP or torque, if your engine is stock.

Hey tompatjr, interesting note there about the OBDII system. Do you know how the system would know that the pre cats or the main cat had been removed? I understand he might replace the main cat w/ a high flow unit, but also sounded like he was steering towards eliminating the two pre cats altogether.
I agree that he wont see a very big increase in power just by eliminating or changing the cats. Overall, just better off going w/ a header and cat-back system. Its just that these late year rigs have those two BIG precats sitting right in your way!

On the '01, remember that there are 2 pre-cats with 2 sensors each. One before each pre-cat and one after (at total of 4). The input sensors are used by the ecu to control mixture. The output sensors are used to check the operation of the cats. You need the appropriate signals on all 4 of them to keep the check engine light out.

I haven't tried this, but it seems to me one way to do this would be to have bungs for 2 sensors welded into the header down pipes for the pre-cat sensors. The post cat sensors could be added after the main cat. The wires to the post cat sensors would have to be extended quite a bit to reach behind the main cat. Hopefully this set up would keep the ecu happy, since there would be a cat between the input and output sensors - only it would be the main cat rather than the pre-cats.

Hope that helps,
Dave

Good point Dave. I never looked at those pre cats too closely yet, so didnt realize there were two sensors AFTER them. The header Id like to go with has two bosses in it for the sensors before them, so Im ok there. Now Im curious to see if the ECU would accept a signal from after the main cat, as you suggested, if the two pre cats were gone. Then again, maybe all we need are the two pre cats and the exhaust would be fine w/out the main.
I think Ive stumbled onto a project for myself! Id say a little experimentation is in order, would'nt you???

BCKNBLK said:

Hey tompatjr, interesting note there about the OBDII system. Do you know how the system would know that the pre cats or the main cat had been removed? I understand he might replace the main cat w/ a high flow unit, but also sounded like he was steering towards eliminating the two pre cats altogether.

Click to expand...

I don't think the OBD II computer really knows anything, only that there is a malfunction of some type with the cat(S). I'll be honest I don't know exactly how the O2 sensor "knows". But since the sensor is nothing more than a O2 monitor, I assume the O2 in the exhaust gases would change some what in the absence or failed cat.

thanks for all of the quality replies...

i don't have anything against the pre-cats necessarily... my problem is two-fold:
i've developed some kind of slight clicking noise which to me sounds like an exhaust leak (so i assumed, perhaps falsely, that it was the infamous exhaust manifold crack). the other problem is that i swapped out my low-pinion D30 for a high-pinion D30, and now the driveshaft makes contact w/ the exhaust flange under certain conditions of the suspension cycling. in fact i'm wondering if in fact this wasn't the source of the purported leak, that is to say maybe it got knocked hard enough to loosen something up. i've tried to tighten the exhaust manifold bolts, which was a bit challenging thanks to those pre-cats right in the way!

eventually i'll need to do something w/ that exhaust flange, so i was thinking an aftermarket header might be the way to go.

actually the third issue, which isn't that big of a deal i suppose, is that the cat on this is the larger cylindrical kind (so i had to notch my t-case skid a bit to fit around it), whereas apparently most others are flatter. :dunno:

BCKNBLK said:

I think Ive stumbled onto a project for myself! Id say a little experimentation is in order, would'nt you???

Click to expand...

by all means, please proceed!

i'll be anxious to hear about your findings. i'd love to do a custom exhaust someday, but if the OBDII is gonna complain, not sure if it is worth it.

:cheers:

I wouldnt know what to do about the interference from the high pinion deal, I havent really done much of anything yet except look into a lot of what I COULD do. Perhaps changing to a certain header will solve the interference problem.
About that clicking noise, just by chance, if you are still not sure exactly where it is coming from, check also the upper left side (pass) of the engine compartment. After first getting mine I noticed a clicking sound from under the hood and thought it may be a sticking lifter. I traced it to a little vacuum dashpot type item bolted to the firewall. Sometimes it clicks loud enough to hear from the inside, and sometimes it doesnt click at all.
The oxygen sensors are simply measuring the levels of oxygen in the exhaust. If their is too much or too little, the computer see's this info from the sensors and adjusts the mixture. You cannot run without them, and the more I ponder over the subject, the more I think I am going to just install the dual outlet header and reattach the two precats, then go with a high flow main cat and a cat back system. That way I will not have to deal with the two sets of oxygen sensors and an unhappy computer.
Yes, maybe I am chickening out. I think those improvements will still net me a decent amount of new power, though.
What is that high pinion deal anyway, and what is it for? Wouldnt a lift take you away from that problem by adding more clearance?
Dave (also w/60th Anniv.Blk. XJ)

I would like to know about this too.

I have a 2001 Sport and a borla header and downtube that the shop says they are physically able to install, but it wouldn't be emissions friendly.

Now, I don't have a problem with it, but my mother does. The thing is that she is willing to pay for the whole thing as long as it can be "legal".

Any updates would be apreciated.

Maybe a tech writeup, or pictures, or diagrams.

~Jeremy