I've been having a weird variable screeching noise that sounds like a vacuum leak on my 97. After replacing all my vacuum lines to no success, I tightened down my manifold bolts as much as I could. It seemingly fixed it for a month, but it's back now. My exhaust manifold was replaced by a shop last year, guessing they did a poor job with the gasket. I am going to replace it, is there any thing I can use with the actual gasket to make the seal stronger? I was thinking maybe purple permatex gasket sealer. I hate the stuff but I don't want to have to do this job a third time. Any tips on the process or sealing is very appreciated.

 

The manifold nuts/bolts are torque specced and generally get tightened from starting in the middle and going out. I have never been able to get a torque wrench on all of the nts/bolts on an XJ, but it's not too hard to tell when they are "good-n-tight". When I do manifold gaskets, I use permatex copper spray. I bought a can awhile ago for a non Jeep project. No idea if it helps or nor, but I haven't' had any manifold leaks on my 98 or 99 XJ or my 95 YJ. A manifold leak would nto make a screeching noise. You would hear more of a hissing where air is being sucked in at a high rate. For an exhaust leak, you can move your hand around (before the manifold gets really hot) and feel for air. IFor intake leaks, you can spray carb cleaner or similar all around with the engine running and if the idle speed goes way up, you found your leak,

 

Ok, thanks. It is more of a whining noise, and at times it will change pitch. This is a video of it, it only happens on the highway when I let off the gas. It is really strange.

 

Remove the air box to do the job.

Sealer is nowhere near as important as correct installation.