accel

I hate to post yet another thread about sounds coming from the engine compartment but i haven't been able to find someone with the same sound as the one my 2001 XJ makes. It is a high pitched whistling sound that follows the engine speed and is most pronounced just after releasing throttle. Does not depend on engine temp or outside temp or humidity, the sound is always there. The following link shows you what it sounds like. Please copy and paste the link (without quotes) into a new tab/window in your browser, I couldnt get the hyperlink to work properly.

"http://finch250cel.tripod.com/sitebuildercontent/sitebuilderfiles/Recording4.wav"

Sorry for the background noise but the engine compartment was open; you can still hear the sound tho, even with my cell phone voice recorder the sound is pretty true. i was revving the engine to about 2k rpm multiple times.

I've taken the preliminary steps of removing the belt and checking all the pulleys for excessive play or bearings that feel busted but everything seems to spin fine. Even the idler pulley, which from what i've read is a suspect, seems fine, i removed it and spun it on a drill and i did not notice any weird sounds or vibrations. The belt is not new but i replaced it a few months back and the noise existed prior to and after the new belt. Ive also played with tightening and loosening the belt to no avail.

The noise isn't heard when the engine is running without the belt, which i assume indicates a pulley/bearing/pump problem but everything seems to spin fine by hand. i feel like the only way to determine the sound is to replace components one by one, but i don't want to spend money unneccesarilly replacing things that arent broken like the power steering pump, water pump, alternator, etc. Has anyone had a problem with this noise before? Any suggestions for probable cause from personal experience without just guessing? Any help is greatly appreciated, thanks a lot everyone.

TrekkerJmm

Welcome to CF from Tj in NJ, That sounds like the throttle body to me, you may want to try cleaning the TB out to see if it helps. One other thing is that someone may have had it bored out which would cause that whistling...Tj

G_P

Since you say it gets loudest when you let off the throttle that makes me think its a vacuum leak since vacuum would increase when the throttle closes.

Check around for cracked hoses or hoses that slipped off of their fittings.

accel

Would the throttle body cease making the noise with the belt removed? Cause as i mentioned, with the belt off the noise is gone. I'm gonna double check that tho once it stops raining. A few months ago i disassembled the TB and cleaned it out, it wasnt too dirty but there was some black soot on the walls. I'll try that tho.

I already checked to make sure all the vaccum hoses were in but i didn't check for cracks in the hoses, just the connections. I'll try wiggling the hoses around to see if the noise changes. Thanks again

ol"blue

With the engine running and avoiding the belt, use a stethoscope on each accessory to listen for the offending bearing noise.

McRay

Had bearing that the cooling fan clutch bolts on that went bad when I change out the a/c bracket it made wearied noise. Might check that and spray belt dressing on each pulley that the belt runs on and see if the sound changes this was on my 2001 Jeep Cherokee Sport 4.0