Snwboarder673

For some reason i have a loud whine coming from under the hood the whine changes pitch and sometimes stops wen i push on the gas pedal but then comes back i was maybe thinking its the throttle valve on the transmission i really dont know i am new to jeeps Someone please help the only thing that drowns out the whine is my radio

xj_maniac_newb

Sounds like a belt squeal to me..

krazynezz

^^x2

Slimgoaty

Check your harmonic balancer (crank pulley), make sure its not grinding in to your timing cover. Also check all your pulleys, especially the idlers.

DFlintstone

I'm thinking vacuum leak. If not a line check the manifold bolts. (if a few easy to reach are loose, you need to remove the air cleaner and do them all, working out from the middle)

You can listen with a section of hose. If you hit a leak with a quick little burst of starting fluid the sound of the engine will change.

Not familiar with a throttle valve on the transmission, Somebody pulling your leg?

Gorillaxj

X3! I bet its loose.

Snwboarder673

Not belt its coming from the rear driverside section of engine bay happens after the car is drivin for alittle and goes away above 1/4 throttle and then comes back

Gorillaxj

Then I would give this a shot. could be the hose to the booster/intake

black2000xj

take that supercharger off the motor see if you still have it

Snwboarder673

Haha wish it was blown

SHO_GuN

Did you track this problem down yet?

Sounds like my exact problem, definitely not a belt. It comes from the rear of the engine bay as you state and also changes based on throttle position.

Mine was going away after around half hour of driving but on my last outing it remained audible the whole trip.

2000 XJ 4.0

winston427

This is a common problem on later model XJs. A high pitch whistle when you let off of the accelerator. The very back bolt on the intake/exhaust manifold will back out a little causing a vaccum sucking air in through a tiny gap in the gasket. This can sometimes be fixed simply by tightening the bolt back to the proper torque specs. Depending on how long it has been doing it, you may need to replace the intake gasket.

The worse the whistle gets with time the more likely it will throw a CEL for random cylinder misfire. The gap sucks in to much air and the computer reads it as a misfire on multiple cylinders as they try to fire.

I have been fighting this issue for quite some time and finally installed a new gasket this past weekend. Have not test drove it yet because I am also replacing the entire cooling system but should have her back on the road later today.

winston427

A quick test to positively locate it is to take a piece of tubing and use it as a stethoscope. You should find that the sound is coming from the intake right at the firewall.

SHO_GuN

First some additional info...This doesn't happen at startup, the noise starts after about 5 minutes of running and had been disappearing after around 15 minutes until the last trip when the noise stayed. Today is unusally warm and the noise again stopped after a few minutes.

However, per your suggestion, I took a hose with me and immediately stopped when the noise started and used the hose as a stethoscope and verified that the noise is coming from the rear of the intake.

I was able to tighten that bolt 1/16th - 1/8th of a turn, so I am very hopeful this was the problem. This is both annoying and embarrassing.

It may be a few days before I can test it with the vehicle overnight cold, but I will be sure to post the results here when I do.

Thanks alot for the help

winston427

It usually doesn't happen at start with the engine cold. But that will change with time as the gasket changes with repeated heating and cooling under a loose intake. Mine started as a mild whistle only when I let off of the throttle at highway speeds. It eventually progressed the point of people staring at a red light because it was so high pitched even at idle.

Be cautious of over tightening the bolt as that make cause more damage to the gasket. The factory torque spec for the rear bolt is only 23 ft/lbs.