2008 4.0L Vacuum leak

Hi Guys,

I have a 2008 4.0L and i've had a whistling noise for a while now. It hasnt effected my driving/milage or performance at all that i can notice.

It happens only when i step on the gas hard and the Rev's go up.Its loud enough to hear with the windows down


I was told its a vacuum leak. Any ideas or stories to share ?

 

A vacuum leak will be more notable at idle or other times when the throttle plate is closed, IE engine holdback. Might be something with the intake before the throttle body, or exhaust related. Is it a smooth whistle sound, or does it pulse / chirp?

 

Its smooth.

 

In most cases, a vacuum leak will cause an engine to idle way faster than normal- similar to an old vehicle that needs "kicked down"
Do you have a cold air intake and/or a throttle body spacer?

 

Does your truck have this fast idle problem?

 

No it does not. I havent notice any changes in the idle. Its a stock engine.

 

Does it make the whistle when you rev it in neutral? If so, maybe check the belt tensioner pulley and idler pulley bearings, they sound a bit like whistling when they are dry and dying.

 

This sounds good, it doesnt make the noise at idle. I'll check this for sure.

 

Mine has a whistle at the same rpm [around 3200 35 mph] and it happened after i replaced the stock alternator?

 

Bad bearing on idler pulley or accessories?