2003 Jeep Wrangler LOUD squeal when coming off the accelerator. I’ve had changed the Tension Pulley, The Belt, Checked the Power Steering, Removed the belt from the AC unit…smaller belt now…Tested the Altenator, it’s working like a champ. I have a 4.0L 6 Cylinder. My mechanic wants to check the intake gasket and another intake which he spoke of and I can’t remember at the moment however with no guarantees these or one of the two could be the problem. He expects it to be a 5 hour job and at $69. an hour that could get expensive. The sound seems to be generated from the lower backside of the engine
HELP PLEASE!!!
Connect a vacuum gauge to the intake and compare the manifold vacuum to the sound. When the engine is revved the vacuum will drop, then when the throttle is released vacuum will jump above 20" for a few seconds. If there is a positive correlation between the squeal and manifold vacuum you would have some(?) certainty that pulling the manifold would solve the problem.
I had a symptom like this on a early 60’s Ford Galaxy I owned, and it turned out to be the valve cover gasket was leaking a bit. Have no idea if it applies to your car though, but I’ll mention it, might be of help. There’s a vacuum under the valve cover, part of the pcv function, and a small leak in the valve cover gasket allows air to stream in and can cause a squealing sound, like how a kazoo works. The intake manifold vacuum is strongest when the throttle valve is closed, foot off the accelerator in other words. So that might be consistent with your symptoms. I’d check the valve cover first if it were my car. It may be that the bolts holding down the valve cover have come a bit loose is all.
One thing you might try is to temporily remove the pcv valve from the valve cover, see if that makes any difference.
The thing that isn’t consistent with this idea of course is that the sound appears to be coming from the backside of the engine. Well, what I said, it’s only an educated guess.