I just replaced my alternator, made sure it was straight with the other pulleys and put my belt back on, now it squeaks when I start it and runs. I was wondering what the belt deflection should be on a 4.0 engine or what could be making it squeak. I also replaced both idler pulleys and still can't pinpoint the squeak.
Did you replace the belt? An older belt can make quite a racket. I know on my 97 I had to replace the serpentine belt about once a year, the dirt and mud would get ingrained into the surface, my 98 has just started squeeking now, I tightened it slightly and that helped.
My ZJ has traction control, I call it my right foot.....
I put a new belt on a couple months ago as regular service. It was a $20 belt from o reillys. I too changed out my alt, waterpump, and pulleys. Two weeks ago the ZJ started squealing like a stuck pig. Turns out its the cheap belt from mexico. A real problem with Chrysler engines. An upgraded $40 NAPA belt... all smooth and quiet
You could also check the condition of your harmonic balancer if it comes back, look at the rubber ring between the two parts of the balancer and see if its cracked or missing pieces. When my balancer was going out it would chirp non stop.
Never trust a Jeep that doesn't leak oil.
I tighten the belt until I get about 1/2" deflection on the longest span or if you can twist the belt 90 degrees over the same span.
I have a Gates belt on my 4.0 with never any squeaks. If you give the belt a good scrubbing with a fine wire brush (and a pick to scrape out the grooves) and hot soapy water all over it really helps with squeaking. Also clean all the pulleys including using a pick to scrape all the grooves clean.
If you run the belt too tight you'll shorten the life of the bearings in your alternator, power steering pump, idler pulleys, water pump, etc.