Hi guys,

I have a 2008 Sport 4.0L V6, SOHC. 230,000 KM on it.

Today I noticed a high pitched sound coming from under the hood. It seemed to disappear when I let off the gas. Didn't get louder or change pitch with gas, it just appeared and pretty much stayed constant. It is there at idle as well, so I was able to get a video when I got home.

I don't think it's a belt or pulley, but maybe I'm wrong. I tried giving the belt a squirt of WD to see if it changed, but nothing happened. Belt is tracking straight on all the pulleys so far as I can see. The sound seems to be coming from further back, almost like it's right on top of the engine.

I used a mechanics stethoscope but couldn't find anything that gave it away. I climbed right up on top and put my ears all over the engine bay, but it just seemed to be everywhere.

If I 'blip' the gas, it stopped and returns when the RPM returns to idle.

Any ideas or things to try to eliminate?

Have a listen, it's most clear around 10 seconds or so. Gotta have the volume up.

 

Sounds like it could be a vacuum leak, use the carb cleaner method of spraying around the engine bay/pipes and see if the idle changes.

 

My lap top audio did not help me hear the noise at all.

A common part to fail and cause a noise other people have thought to be belt related was the camshaft synchronizer.

With the mileage you have on your truck I am guessing it should have been replaced a few times already.

It is certainly worth inspecting

Here is a video that may help narrow down the noise.

 

Thanks, yeah the sound is pretty hard to hear on the video, but very easy in person.

I Have a 4.0L V6 SOHC, so I don't have a mechanical cam syncronizer like the 3.0L engines do, I have a small hall-effect style sensor. I've read up on the cam synchro fail and how that can lead to loosing your oil pump if it's not replaced and so on, but thankfully for me that doesn't seem to be a factor on my engine.

 

My Bad the 3.0 in 2008 has the camshaft synchronizer your 4.0 looks like it just has the camshaft sensor.

Sorry I could not help especially since I cannot hear the noise on my PC.

Have you tried disconnecting the serpentine belt for a short test to see if the noise disappears?

 

No problem, I appreciate the suggestion anyway. I haven't tried removing the serpentine belt yet, but it's my next step!

 

Odd noise coming from an engine.
What I heard sounds like coil wine coming from a noisy capacitor on a video card under load.
Or a noisy filament in a light bulb just about to burn out.
Very high pitched...

My best guess is it's coming from the alternator.

When you run it with out the belt, that will tell you that at least it's coming from the front.

 

Yeah its weird hey. Your description is spot-on. I used my mechs stethoscope on the alternator but didn't hear anything. Removing the belt should help narrow that down. I'll report back...

 

An engine stethoscope doesn't/won't work well with really high pitched sounds like that.

 

Think it's fixed! I removed the IAC and it was very black. It seemed to open and close ok, but I flushed it with throttle body cleaner and used q tips to clean it out.


Then I started the truck and sprayed into the throttle body on and off for maybe a minute. The throttle body did not seem overly dirty and oily inside to me.


Put it all back together and had a listen. No sign of the high pitch whine anymore, and the idle dropped down to 750, nice and smooth. I'll keep and ear open next few days but this seems to have been the fix. Thanks guys!

 

Sweet.

Sooo, do i get internet points?