Whistle while decellerating

[Just4Funsies]

I have seen a couple people write about this before. It seems to be a common problem with Jeeps. When I let off of my gas pedal, I get a really loud whistle from my engine compartment. It only happens after I have been going 45 MPH or over. It usually stops when I come to a complete stop or if I press on the gas pedal again. If I depress the pedal a little bit, it becomes less loud. If I push the gas pedal further down, it usually stops. I need to know where to look for a vacuum leak if it is associated with the fuel system. I don't want to blow myself up checking for a leak. Can anyone help? It sounds like its coming from the driver side wheel well. Thanks.

 

[88Wrangles]

Could be a vacuum leak. When you let off the gas is when the most vacuum will be present. It could be any of the lines though, so check them all really good. If you can get ahold of a smoke machine it would make things a lot easier for you too!

Also, is your air box and intake all stock still, or do you have anykind of aftermarket stuff on there (like a 'cold' air intake)?

 

[88Wrangles]

I need to know where to look for a vacuum leak if it is associated with the fuel system.

What do you mean by this? Vacuum lines and fuel systems aren't usually associated with each other. Fuel lines are under pressure.

 

[90Xjay]

You should do a search and read up on the PCV system in the 4.0's and how to correct problems, if it is not a vacuum leak then maybe you are hearing the air pass between the throttle body and the butterfly.
Did you just recently install a cone style air filter.
Boy I did that to mine and I kept hearing a whistle and I figured out that with the aftermarket breather you can her the throttle body louder. No problem.