2.5" is definitely the way to go. It's been on my '92 since before I bought it and I'm really glad. This 4.0 has a lot more pep in it compared to other 4.0's I've driven. I have a k&n intake on it, but I believe the seat of the pants action is more owed to the exhaust than the "cold air intake".

Here's an example that can be applied to the situation. Now, this is 3" vs. 2.5", but it's on a v8. So you can see how easily the example can be applied for 2.5" vs. 2.25 or 2" for the inline 6

This seems like a good place to ask this. Pardon the forum fishing, but I'm just gonna copy/paste this on in here and hope for the best.

I've got a 2000 Cherokee Sport (XJ, I'm told), 4.0L inline 6 4x4. Had my valve cover off the other day (CCV breather complications) and when I closed everything back up and turned the key, everything seemed groovy. Drove 8 miles into down (windy canyon road, 35-55 mph), stopped to grab something from the gas station, and then went through a drive through. After I finished eating my food in the parking lot, I started old JeeP back up , and that's when things got dicey.

Took a little longer than usual to turn over, and sounded like it was struggling to do so. Engine was shaking pretty hard at idle, white smoke was sputtering out of the exhaust, accompanied by dribbles of fuel. Oh, and the check engine light came on.

I decided to see how it drove to the grocery store across the street (intended destination, and easier location for the likely auto-club tow) and the engine light started flashing. The manual foretold great misfortune, so I went with the tow after all.

So that's where I'm at. Wondering what the problem is, and how I can fix it. I've got a couple of suspected causes, but I'm new to mechanicry, so I'm reaching out here to suss them out.

There were a few complications while I was replacing the valve cover. First, I lost one of the bolts in the back that I ended up finding in a bundle of cables/wires running back on top of the transmission (you don't even want to know how long that took me to recover), so there's a chance I may have jostled something out of position in the wiring/connections behind the valve case and above the transmission.

... and then I snapped a bolt, and spouted some curses. In the process of loosing that bolt, I had to remove the coil pack, and it was something of a struggle to get it back into place.

Now, through parts of this process, I had to literally climb up on top of the engine area, taking care of where I distributed my weight... except for when I accidentally cracked what nearest I can tell is the fuel injector wiring harness. Plastic casing that runs along the driver's side of the valve cover, out of which the fuel injector pigtails feed.

Recent Jeep history: Had what turned out to be a failing freeze plug that I replaced with a rubber one, after getting a metal one which turned out to be a bit too small. Before I discovered the freeze plug issue, I overheated a couple times (the second being pretty significant), and there were also a couple instances of a load whistle that would go away when I depressed the accelerator.

Thought everything was cool with the freeze plug fix, and after about a week of driving about 150-200 miles, I decided to change out that CCV breather (contributed to a failed smog), and the elbow cracked...

Which brings us up to speed.

Any thoughts on what I can do to get JeeP up to speeds higher than parked? I'm really hoping it's just a plug/wire that came loose, what with my limited access to funds and specialized tools.

You won't get any answers here. Repost in Oem.

Done. Gracias

Is there a way to get rid of the California pre cat stuff on an 01 and run a normal system? I still want to run a proper cat I just don't want the stupid pre cats and 4 O2 sensors.

I assume I would have to replace the 2 piece header with a 1 piece, replace the downpipe or weld in an O2 bung and same thing for the cat. Probably would need a new ECM as well. If this is even possible what would I do about the 4 O2 plugs? Would I only use 2 or maybe splice the 2 upstreams and 2 downstreams together and wouldn't need a new ECM?

Any advice or opinions is appreciated. I'm just sick of dealing with the cali emission crap and need to replace the entire exhaust anyway.

they wont want you talking about removal of these things on the forum, they're very nit-picky about it. If the car comes with the cali pre-cats, you'll need to work with that on your own time or find someone off the forum to talk privately about it. just to save you the trouble and upset moderators.

Yeah, I wasn't sure if they'd be ok with it or not seeing as I still want to keep it legal and run a cat. Figured it was worth a shot.

Edit* Did some more research. I thought as long as I had a functional cat that I would be legal. Not the case, sorry guys.

Yep. Not legal to remove, and not allowed to talk about here.

not a problem, it's not bad to ask so long as a straight answer is given. I'd been talking with my garage guys after i had mine in for inspection and since I'm not in cali the tests/requirements are different, but the car came stock with them so legally they need to be retained. It doesn't exactly help what you were asking, since you still need the o2 sensors and everything else, but there are a couple of aftermarket precat options, i believe the one most commonly talked about is a walker precat but i'm more partial to the magnaflow i want to get on my exhaust redo. if I remember correctly, the walker precat had some odd/annoying placements for the o2 sensors.

I had a flowmaster 44 on mine and it sounded right

https://www.youtube.com/watch?v=IsD-...ature=youtu.be

This is my Jeep Cherokee Sport with a straight pipe. It only has the cat on then a 2.5 inch wide pipe going out. Its a full run as well. Not a short straight pipe. If you have any questions about the set up reply to this or send me a message.

Can anyone help me figure out how the heck to remove these damned pre cats? I need to replace them and I have the new part I just can't seem to get anything on the damn bolts to get the old one off. I've tried wrenches of various lengths and shapes but no luck. I've tried sockets both deepwell and shorties, with and without a swivel...no luck. Do I have to take the headers off in order to get to the bolts? If I do need to remove the headers I would have to install and tighten the pre cats while out of the vehicle and I'm not sure how the heck I would get them aligned correctly outside of the vehicle.

I run a cherry bomb bullet shaped glass pack on my 1999 xj 4.0 it has a louder and more pleasing sound than stock or the Gibson cat back system I had on it.All of these mufflers are not the same,as some brands the inner tube is around 2 inches and only the outer ends are sized so the muffler could be cosidered a restriction. Another thing is the muffler can be mounted 2 ways,with the inner louvers in an aggressive direction or a passive direction. I have heard the cherry bomb don't work so well o the 2.5 4 cyl ,I don't know from experience,as I run a flowmaster on my 2.5 xj , it loud but has a good sound with no weird interior sounds. Thanks

Ok, I need some advise. I'm pretty sure that my stock exhaust manifold has finally succumbed to age and heat, and cracked. I'm thinking that I want to replace it with an Armor Coat Jeep Header 1997-99 Cherokee 4.0L w/pre-cat from Pacesetter. http://www.jegs.com/i/Pace-Setter/766/72C1190/10002/-1
Couple questions....what is meant by "w/pre-cat"? From looking at the pic in the above link, am I correct to assume that they mean an 02 sensor before the catalytic convertor?
Does anyone here actually have this Pacesetter header on their Cherokee? I know that Pacesetter advertises this Long Tube header as increasing low and mid range RPM torque as well as increasing overall HP. Would this header be a better performance ad-on than say, the shorty headers available from places like quadratech. yeah, I know, but the Borla long tube headers are only available for the 93-97 Cherokee and apparently won't fit my 98 Cherokee Classic. So whatcha think? Would the pacesetter be worth the investment?

You see how there's 2 tubes separate from each other before it goes into the collector? Yeah... there's 2 small catalytic converters that go there (not included, obviously). IIRC, those are for California Emissions Jeeps only... so if yours is federal emissions, you don't need the cats. You can still get that header, I suppose, and weld it together instead of putting the cats in, but I'd imagine it would probably be less expensive to just find a Fed emission header

Here's the 2 pre-cats: