I use to own a 95 xj and it was a power house. I had plenty of low end torque along with high end speed. My 2001 xj isnt the same. Ive changed spark plugs, but thats about it. Can someone tell me some things i could due to get more out of her. I had also heared that if i put a manifold from an older model it would get a few more horses. If that statement is true with models will fit my 01?

 

The intake statement is completely the opposite. A none HO motor gets a few more horses from an HO or 97+ intake.

 

have you checked the air filter, fuel pump the normal tune up stuff. I'd start there. what are you long term plans for it?

 

I made up a cold air intake for mine and it added a fair bit of pull especially off the line. i've also heard about throttle body spacers but i've yet to try that out. hth

 

first, get a baseline with a complete tune-up: (plugs, wires, distributor cap, etc.), and then, have your fuel rail/system pressure tested and check for leaks around injector o-rings (may need replacing - if so, do all of them) and your battery/starter/alternator load/charge tested.

to feel the real power of the 4.0L H.O. ....... you need massive amounts of cold air volume to see real performance....and a healthy fuel and electrical system...
1. yank the stupid air box and replace with a 3" x 12" stainless pipe, with one vacuum inlet, and a 3" x 12" open-cone filter.
2. replace the choking 58mm TB with a bored 62/63mm TB and modified brass blade.
3. install a 1" 62/63mm TB spacer.
this will get you going ....really fast ....cost less than $400 and maybe 1hr diy to remove/replace/install all - gotta disconnect battery to reset ecu and let it adjust to new environment....take it for a spin, but word of caution - be careful, cause you're gonna love it!

then, to keep the liquids cool....
4. replace thermostat with 180 degree plus one
5. replace water pump with better built, hi-flow one
6. i've been using synthetic oil for a while now (127k miles), i also use Hi-performance, higher capacity mopar/fram oil filters
7. replace fuel pump and fuel filter with better ones
8. new injectors and o-rings - replace with 19# Ford injectors - they have quad-ports instead of single, for better atomization.
9. replaced fuel tank - jeeps are notorious for crappy tanks that deteriorate from the inside-out and start damaging your fuel components!
10. brand new Interstate (Optima quality is crap since they moved production to Mexico!) hi-crank battery - if the juice is low, you will have all kinds of issues because everything depends on correct voltages for adjustments by the ecu.

planned....
11. remove engine (mechanical) fan, it's really heavy, and wimpy electric fan and replace with dual 16" electric fans with hi quantity low profile blades- much lighter and way cooler.
12. replace intake manifold with 2001 manifold - better flow design, practically no right-angles - every 90 degree bend is ~2.3 feet straight!
13. upgrade brakes in front
14. replace stock shocks and steering dampener
15. replace all mounts/bushings with polyurethane ones
16. stainless steel 2.75" exhaust system - headers to tail pipe
17. this is enough for a while....but, i have more!

down here, keeping it cool is number one priority. next, loose the weight, the lighter the load the faster you will go - i'm running all stock, except for above - it flies off the handle and keeps going over 110mph, then it kicks down into 3rd wanting to go even faster - haven't dared to go over 110-120 in a 1/4 mile stretch! the rest of the time it just seems like it's floating on air - literally, you can hear it sucking fresh, clean, cold, unobstructed oxygen. my mpg is excellent.

i'm working on a similar setup for my 2001 mercedes e320 v6, it roars and sucks it all in, too. also running similar setup in my 2010 vw cc 2.0L Turbo - the turbo screams, spools and lets loose like a banshee!

 

I have a magnaflow on mine sounds great and its very snappy the 4.30 gears help too. I plan on getting some new fuel injectors out of a ford. They're basically the same injector but these ones have four spray holes instead of one which atomizes the fuel better. This results in better mpg which means more horses. this is a great write up on it http://www.lunghd.com/Tech_Articles/...r_Upgrades.htm