I am having the same issue as this guy did in this thread:

https://www.ranger-forums.com/2-3l-2...le-only-39300/

on my Ranger. I have a 2002 XLT Ext Cab 4.0 V6 4x4 Off-Road with 79,000 miles on it. The squealing noise is not RPM dependent but only at a certain throttle position. It's really difficult to reproduce the sound stationary. I even tried lifting the rear and putting it in drive to try and pinpoint where the exact sound is coming from but it seems as though I need to be actually driving so it has a load to move.

I have a K&N 77 series air intake but it's not that because I took the entire piece off so that it sucked in air from the intake valve and drove around the block and it still made the same sound at the same position. I checked the IAC, wiped it off with a rag and it looks good. There are no idling issues like others have said and no problems accelerating.

I also took a look at the PCV and the hoses look fine, it doesn't collapse while the truck is running either. I didn't take it off but by the looks of it, I don't think it's the issue.

The sound is coming from the engine area though near the throttle body. Could it be possible my EGR has a leak?

Thanks

Update: I'm thinking it might be the throttle body base gasket per this website forum as this person is having the same issue I am:
http://coloradok5.com/forums/showthread.php?t=225161

 

Yes, could be an air leak in throttle body or throttle shaft.

Usually that would also produce a high idle after warm up, i.e. above 850rpms.

Is it hard to get the noise while in the driveway or impossible to get the noise?
That would be important since engine air intake noise wouldn't be dependent on motion.
Engine load does change vacuum in intake, can you test if there is more or less noise going uphill, higher load, at that throttle position?

 

This is a long shot but it is easy to check out. There a rubber elbow that is on the right, front side of the upper intake. It is under the upper radiator hose. It connects to the hard tube that goes back to the PCV valve. The rubber degrades over time and can crack. When mine cracked it did not make any sound but did idle rough. It could be that yours is cracked in such a way that it makes that noise at a specific air velocity. If you don't have a rough idle, the elbow is probably not the problem but still worth checking out.

I found my vacuum problem by carefully spraying starter fluid around the intake area.

 

Ron, thank you for your reply and insight. I just changed the throttle body base gasket and cleaned the **** out of the intake. Man does it run better but the noise is still there! My Dad and I lifted the rear of the truck in the driveway and put it in drive and it did not make the sound I think it is dependent upon motion. The truck does make more squealing going up a hill. Could it be the fan clutch or alternator bearing maybe?

Gary, thank you as well for replying. The PCV hosing looks okay to me. It's flexible and sealed nicely. I didn't remove any of it though yet.

 

So it is most likely air flow thru the rad or rad support causing the noise, and that could be associated with the fan speed at that time, so throttle position is a factor but not the cause.

Try cleaning out the rad/AC condenser fins, i.e. spray with water and brush what you can reach while doing it.

Failing fan or alternator bearing would make the noise regardless of motion, it would be strictly RPM based

 

The sound only occurs at a certain position, any more throttle or any less doesn't make the sound. It occurs maybe 20-30% down. Any more than that it won't make the sound. Also as it shifts, the pitch of the noise changes a bit as well. I don't think the rad fins would be the cause.

 

Not the rad fins alone, the rad fin air flow and the fan speed combined.

 

I'm not sure I understand what part you're talking about?

 

It isn't a part.

The noise only occurs when moving, so only when air is flowing thru the grill and rad.

And the noise also only occurs when engine(fan) is at a specific range of RPMs(throttle position)

My guess, and it is only a guess, is that there is an interaction in that air flow that is creating the noise.

Like side mirror whistling at a certain speed, lower speed no whistle, higher speed no whistle.


You could try putting a piece of cardboard in front of the rad, like people do in winter to keep rad/engine warmer, then go for a drive and see if noise is gone.

 

Now that I notice it, I just held my brake down in the driveway as I hit the gas and it does make the whistling noise. It doesn't depend on motion but what gear it's in; can only be in drive or reverse (or 1st or 2nd gears)

 

OK, but you said you jacked up the rear wheels and had it in gear and there was no noise.
That where the "must be air flow issue" came from.

Brakes, especially disc brakes, can make noise

 

When I had the rear wheels up, there was no load on the truck, but when I apply the brakes, it's trying to accelerate.

I think it's just getting worse. It almost makes a leaking noise now. It's not coming from the brakes at all but from the engine. I just changed the pads and the rotors are fine but the sound has been occuring much before the change.

 

i would guess it is your clutches throw out bearing that is generation that noise