Crazy noise under hood???

[Lazzman]

Recently my '98 Sport has developed a strange whirring noise, it seems to be coming from the vacinity of the engine bay. It sounds like some type of electric motor that is spinning out of control.

It only happens when I am cruising on the highway and I take my foot off the accelerator. The noise will come on and not stop until I put my foot back on the accelerator. There is no check engine light and all gauges are reading normally, including the tach. Drivability of the vehicle is normal.

I am thinking it may be the clutch in the auto trans allowing something to spin like crazy when ever I let off the gas, but that is just an educated guess.

Any idea's what this could be?? Just want to know if it is something that requires immeadiate attention or will leave me stranded on the road on a cold winters night.

I guess the first question to ask is what occurs in the drivetrain when your foot is taken off the accelerator at cruising speeds to cause this sound? What ever it is, it sounds like it is spinning extremely fast. I guess it could also be the alternator?

Thanks for any input.

 

[ThePhoenix]

IAC? They are known to howl....

 

[Lazzman]

I will check it out. Would the IAC act up just under decceleration?

It sounds like turning on a vacuum cleaner and the pitch seems to increase as if something is spinning faster and faster. It is almost like a shaft and sprocket that is not lined up on teeth that is just spinning freely.

Once again this only occurs when I take my foot off the gas and coast, at speeds over 40 mph. It stops when I put my foot back on the accelerator.

If it was the IAC wouldn't it do this all of the time?

 

[ThePhoenix]

i will let the people who are more professional answer...I am just a greenhorn novice

 

[Lazzman]

I don't know if this had anything to do with it but we had a bad snow storm on Sunday. I had to put my truck in 4 wheel High to get over a snow bank in my drive way and spun the tires hard.

No issue with coming in and out of 4 wheel drive, but the next morning the noise started on the highway.

 

[Rusty]

did you remember to turn the 4wd off?
sometimes we overlook the obvious!
My neighbor moved my ex for me and he put it in 4wd and i was driving down the road and found it in so i switched it off again!

 

[Lazzman]

Good suggestion, I did check and the 4wd is switched off.

Next step is to check the transmission fluid.

 

[tipdrill]

My '00 2WD does this around 40-45mph. There was a post on this not too long ago. They said something about the bell housing.

 

[Lazzman]

Yup, it sounds like it is in the vacinity of the bell housing.

Sounds like a gear spinning & whirring out of control. It only happens when you take your foot off of the gas and coast, mainly at highway speeds. It stops when you put your foot back on the gas pedal.

You can feel the vibration from the thing spinning or humming at high speed.

Did notice that it happens when the tach drops below 1500rpm.

Do you have a link to the thread tip?

I wish I knew what it was, I am concerned that the bell housing or transmission is going to explode.

BTW my wife explained the noise as sounding like a vacuum cleaner, which is pretty accurate in my opinion.

 

[Lazzman]

Turned out to be the Transfer case. Had to have my repair shop do the install with a used Transfer case, still set me back $1100 big ones, which sucks around Christmas time.

I guess I can't complain though, I do run the truck hard and with 210 (Henson Tuned) rwhp, I should have expected the Transfer case or Tranny to go especially with over 167k mi on them.

The four wheeling through the snow, coupled with the extra HP and my new super Grippy 255/70R16 Cooper Tires was more than the T case could handle.