Hi everyone, its me again with another problem, I have a 2000 Cherokee Classic with an automatic and 4.0
I have replaced the water pump, altenator, A/C compressor, idler pully, powersteering pump, and belt... i get a really bad screaming noise when i start up and it last for about 30 min. untill the motor warms up, when i take the belt off it goes away.  when it rains it comes back really bad or when i wash it...  CAN SOMEONE HELP ME  

Did you change the belt tensioner? you didnt mention it, cause the bearing can go out and make that noise too. Or the tensioner istelf has lost its tension and is making the belt loose and squeel like a pig.Do you notice considerable amounts of belt movement?And have you ever replaced the tensioner cause thats a part that doesnt last the life of the rig?  hpoe that helps  

YES, as i mentioned i replaced the Idler pully which is the tension pully, the belt will go as tight or loose as i put it!!! Thanks  

The belt tensioner and idler pulley are NOT the same thing. the tensioner has a pulley on it ,yes, and its between the alt and crank pulley and then you have just a pulley on a bracket mounted between the alt and wtr pump thats called the idler pulley.  

NO, I have an idler pully that is adjustable for the tension!!! i do not have a "tensioner"  as you call it. the only things that have pullys is the water pump, alt, power stearing, crank, fan and A/C compressor... today i replaced my alt. again b/c i was wondering why my battery wan't staying charged, i took it in and it turned out to be bad but that still did not fix it.  

Inspect that there is not a mis-alignment between any pulleys. Make sure all accessories are tight and installed correcly. Dress all your pulleys with steel wool to clean-up any rust or glazing.

And don't use anything to lubricate the belt. Belt dressing, wd40, silicone. That's bad. If you already have, get a new belt and dress your pulleys with steel wool.  

Here is your belt routing in case there are any questions.

http://i286.photobucket.com/albums/ll98/ftgiles/1213398680.png  

Ok, I have done all this, i have went throught 3 belts b/c people have told me " Its just your belt" but it isn't. What i am mainly wondering if anyone out there has had or known of this problem? I have had people tell me its the cam, crank bearings, the belts, all of the pulleys, my timing chain, my valves, my lifters... the list doesn't end but the problem doesn't go away, lucky me it was a free jeep and now i know why... I pray my rubicon doesn't do this to me later on  

similiar with my friends wrangler. tho his lasts like 30 seconds. id say anything with high pitch noise your best bet is crankshaft or alternator. can you discribe the rhythm of it? is it constant or up in down in pitch?  

It is extreemly LOUD, it is very high pitched, it "sounds" like it is the belt and it is very constant, while reving it just gets louder!!    

i would say inspect your intake manifold. how many rpms are you running at idle?? other than that no idea? exactly why it was free haha. i say resell unless you have a lot of time on your hands.  

o hahah im an idiot. its ur throttle body timing is off. idk how to fix it but same thing in my chevy silverado.  

I'm ideling at about 750 rpms untill i put it in drive then it jumps to about 1200. i'll check the timing this weekend... thanks  

I have an XJ, too. When I replace the belt and crank the adjuster bolt, it has to be pretty tight, or I get a squeal... I have to set it tighter than I'm used to setting other belts... Somehow, on my XJ, a new belt seems to want to squeal more (at first) so that would explain why the 3 you've tried don't fix the problem.

Then, after a few hundred miles (when the belt relaxes a little) the noise may come back, and I re-tighten it, then it's good for >30K miles. Haven't had any problems with this method.

Have you replaced your fan clutch? That can squeal when it gets worn, too. If tightening the belt doesn't fix it, it could be your fan clutch. Simple to replace... Good luck.