Hi all,

This is my first time posting on this forum, and you guys seem to know a lot. I have a 99 Expedition 5.4L that makes a kind of "airy" high pitched hum, but only when you let off the gas and the truck's in gear. It kind of sounds like those toys kids have, you know, the plastic tubes that whistle when you spin them around? but it only does it when I'm in Drive and and I let the gas off - I can't duplicate the sound sitting still.

Any ideas?

XXL

 

I certainly don't know alot but my guess would be something in the driveline. Where is is coming from?

 

>I certainly don't know alot but my guess would be something
>in the driveline. Where is is coming from?

I thought about that, but it sounds like it's coming from under the hood - I found out today that if the truck's been sitting, when it hits fast idle in the morning and you put it in gear, it makes the noise for a second. I'm going to have my girlfriend sit in there, foot on the break, and put it into reverse while I pay attention. Hopefully I can isolate the noise.

My suspicion is that it has something to do with the intake - It did it before my K&N FIPK installation, but it seems to be louder now. I'll let you know of my findings...

Thanks for the reply

XXL

 

OK, I am lost now. You said in gear. Does that mean you are moving or just putting it in gear? Let's hear the details of your test. By the way, make sure you are out of the way when your girlfriend has her foot on the brake while you are looking. My wife always has this evil grin when I ask her to do things that might kill me.

 

Test didn't work...

Anyhow, it only happens when there's a "load" on the engine (when it's in drive or reverse). Can't get it to hum when it's in park. I also have to rev the engine above 2500 - it's really apparent when I rev it up, but it doesn't shift, so it decelerates (engine braking) as soon as I let off the gas, it happens. It can be best described as a hum, but high pitched. I think it's some sort of intake or vacuum leak. I've put on a K&N FIPK and it seems to be louder now. I also replaced the PCV valve. Maybe I yanked a hose loose?

XXL

 

This could be caused by the thermostatic clutch fan,
the hub itself is fluid filled with heat or cold could be causing your noise.

also powersteering pump or altenators can cause noises

Try turning on all accessory's at idle

have you changed back to stock filter setup to see if it goes away?

just some thoughts!

Rich


Ford Trucks Built Tough!
not with rocks
Watch out "X" Mayor of Truckville

 

I haven't tried putting the stock intake back on, because the sound was there before...

I think it may have something to do with a hose...can't shake the feeling....

I doubt it's the alternator/PS Pump, 'cause it's got a "breathy" air sound to it...it sounds like air is whistling back through the intake when I let off the gas, and it's whistling at me...


XXL