What is wrong now? Loud squeaking at idle...

I've got a '90 XJ AW4 4.0 with 169k miles. I took it on a 3 hour trip last night, and as I was nearing home, I started to hear a loud, high pitched, squeaking coming from the engine bay. The noise only happens while at idle, or when I take my foot off of the gas. I stopped and popped open the hood, and it sounds as if it's coming from a pully on the water pump or alternator. I can't really tell.

The waterpump is less than two years old, and the alternator is less than six months old. The belt is in good condition.

Any idea as to which pully might be causing this?

Thanks!

I would first check the idler pulley to the right of the A/c compressor. Spray some wd-40or other penetrating oil on the back of the bearing and see if it goes away. Mind you this will not cure or fix it, just possibly diagnose it. If that doesn't work check the harmonic balancer and see if that isn't starting to separate. If you see the rubber coming out of it or it's rubbing against the timing cover, it probably needs replaced. If neither of those are the cause of the squealing, try to carefully use a rubber hose to your ear like a stethoscope to try and pinpoint what accessory might be causing the noise. Good luck.

Which pully is the idler pulley? Sorry for the dumb questions, but I'm a Jeep noob.

Also, where might I find directions to replace it? I looked in the back of my Haines manual under "idler" and under "pulley" but it does not show a listing for either.

Should I replace the belt at the same time?


Thanks

The idler pulley is below the a/c compressor and slightly toward the driver's side of the vehicle. It's the pulley that isn't on any piece of equipment -- it's just there to allow the serpentine belt to make a turn. You can see a picture of it in the Quadratec catalog or on thier web site, and they have as good a price as you're likely to find.

Once you locate it, try squirting some WD-40 or PB Blaster on the bearing. If that stops or reduces the noise, you know you've got a winner.

By all means, replace the belt if you replace the pulley.

Hmm the noise is coming more from the middle or more so on the passanger side than the driver's side.

The belt looks great, and is $35, while the idler pulley (if even my problem) is $25. Don't want to drop an extra $40 on the belt of it isn't needed.

Yep, most definitely the idler pulley. My 94's pulley self destructed (literally, bearing spun right out and completely bent the pulley). It also shredded the belt. Not an expensive fix, but a pain in the ass for sure.

90Pioneer said:

Hmm the noise is coming more from the middle or more so on the passanger side than the driver's side.

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I didn't say the idler is on the driver's side. I said it is below and TOWARD the driver's side relative to the a/c compressor.

Near the middle would be about right.

i would check to see if the harmonic balancer isn't rubbing the timing cover.

Alright.. sounds like it is the idler pulley... any write ups on how to replace it? I can't even find the damn thing in my Haines manual. Anybody know where to look?

While I'm in there, should I replace anything else besides just the pulley itself and the belt?

What will happen if the pulley entirely goes out? Will anything else be damaged besides the belt? Will it still be driveable (as in to get home)?

Thanks for the quick diagnosis, as usual!

loosen the tension off the belt. then you can remove the bolt that holds the pulley to the bracket, then readjust the belt.

jneary said:

loosen the tension off the belt. then you can remove the bolt that holds the pulley to the bracket, then readjust the belt.

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How do I loosen the tension on the belt?

Where is this harmonic balancer located? I have exactly same broblem but I think I can smell burnt rubber when I hear the noice...

HEKULIINI said:

Where is this harmonic balancer located? I have exactly same broblem but I think I can smell burnt rubber when I hear the noice...

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Ther harmonic balance is also known as the crank pulley. It's the largest pulley at the bottom and it has grooves in it for the serpentine belt.
The commonest pulley to go out is the idler pulley which, as Eagle mentioned, is just below and to the right of the A/C pulley when viewed from the front. When the bearings start to go, you'll hear a screaching noise which becomes louder as the condition gets worse. Eventually the noise suddenly stops and that's because the pulley bearings have seized altogether and the pulley isn't turning at all. The result is that the friction of the belt constantly rubbing on the pulley produces a lot of heat and you smell burning rubber. If neglected, the belt will eventually snap and leave you stranded.
The cure is to replace the pulley and belt. You need to loosen the belt first and to do that, you need to loosen the bolts of the belt adjustment mechanism below the PS pump reservoir. Once you've got the belt off, remove the pulley retaining bolt with a socket wrench and pull off the pulley.

i'm not saying the idler pulley isn't bad, but i have changed far more crank pulleys than idler pulleys. if you take the idler pulley off, you should be able to spin it in your hand holding the center part still. if it turns freely and isnt grinding it may be ok. if it doesn spin smoothly it is bad.

Jneary has a point. My primary XJ is an '88. I have had a "squeaking" noise caused by the idler pulley, and again by the harmonic damper. Check both.

To remove tension on your serp belt: The power steering pump is your tensioner. It's easiest to access if you remove the air box. The actual tensioning screw goes in from the driver's side and is horizontal -- it points from the air box toward the water pump. HOWEVER -- before you can adjust the tension, you have to loosen four or five bolts holding the pump bracket in place. IIRC two are accessible from the front, and three are accessed from the back of the bracket. If you don't loosen them all, the bracket won't move.

Well, it turns out it is not the idler pulley. I just took it to a pretty good mechanic here in town and they looked at it and determined the squealing noise is coming from the alternator. They checked the fan blades on it, and they weren't hitting anything. A visual inspection and charging test was OK.

I had the alternator replaced four or five months ago by another mechanic, and it's a NAPA brand alternator. I'm going to take it back to them tomorrow morning.

Any ideas on what could of caused this?