(fixed) Engine whine I cannot pin down - definitely related to serpentine belt

[gladesteen]

This morning, my 04 Bravada started this whine noise that i cannot figure out! I've had a scope on all the pulleys, changed the idler as it is normally the culprit.....nope!

I took the serp belt off and started her up......whisper quiet.
SO its definitely something with a pulley/or belt related.

Here is what i've done to try and figure this out:

- Changed the idler pulley.
- With belt off, i hand spun all the pulleys. No gritty/grinding noises or feel at all.
- Scoped/hose tested every pulley (Water pump, alt, tensioner, etc) all are quiet.
- Took bravada to two different shops. They cannot narrow it down either.
- Its RPM (low rpm) noticeable very easily. You can easily hear it at idle.
- Sound increases with small throttle imputs and then goes back to a "whine" at idle.
- The water pump and clutch fan were changed last fall.
- The water pump is tight. Zero play. I dont suspect either the fan/WP.

One shop suggested it might be the alternator on its way out. Even tho you cannot hear anything with a scope.

Again, this just started this morning on startup.
No codes, and nothing pending either.

It 'kinda' sounds like a power steering pump on its way out just to give you an idea of the noise. By the way.....i checked PS pump and fluid. Both are good.

Any ideas?

 

[Harpo]

Have you checked the smell of your Ps pump fluid?.
If it smells anything like it is burned compared to new fluid it might be on its way out.
Mine was starting to make some sound a couple of days ago, topped it up and much less noise.
It could be that it is on it's way out, iirc it was starting to make some noise before it went out a couple of years ago. The axle snapped right of inside the pump, bit still kept together in its place.

 

[gladesteen]

yea, checked and re-checked. The noise is not coming from the PS pump area.
There is normal noise from PS when moving the wheel. This noise (whirl/whine) is only gas / engine related.

 

[Harpo]

Strange.
There is a overpressure valve inside the pump that can make the sound come from the pipes/hoses.
Try and take the lid off the Ps pump and see if the sound get much worse.
I don't know what else it could be that makes that kind of noise and not be fairly easy to pinpoint as alternator or ac pump,everything else you have replaced already .

Has the Ps pump been replaced before?,what is your milage?.

 

[gladesteen]

Hey harpo,

I took the truck to two shops that i trust after a couple hours of me hose listening/long screwdriver attempts. They both scoped and checked everything. Its SOO frustrating to not narrow this down!

The bravada just turned 171,000. The alternator is original as is the PS pump.

The reason i added the PS 'sound' example was to give you guys an idea of what it sorta sounds like. It is not necessarily a PS whine noise, but more of a whirrrr.......hard to explain. Maybe tomorro am at cold start, ill take a vid.

Thanks,
Mark

 

[littleblazer]

A/c compressor pulley?

 

[Harpo]

That would probably help a bit with a video.
I had a problem with a Chrysler T&C that I had before the TB.
A strange sound that was very hard to pinpoint, it turned out to be the tensioner spring was bad and caused the belt to shudder creating a strange sound. The tension wasn't enough on the belt.
Check your belt for vibrations and shuddering.
See if you can increase the tension by pushing the tensioner with a long something , to see if the sound disappears. Be very careful though of all moving parts.

Only thing I could come up with for now.

Janne

 

[christo829]

You changed your idler pulley, but did you change the tensioner pulley as well?

Usually if it's one of the other components, you'll hear *something* through
the stethoscope.

Last time I had a tensioner go bad, I was able to get some penetrating oil in
to the bearing, and it quieted down until I could swap it out. Might be something to test.

Good Luck!

Chris

 

[Sir ffeJ]

Tensioner pulley was my culprit.

 

[nopaybob]

Electric clutch fan, I put at least 4 on during the time I had my TB

 

[gladesteen]

Hi all, just wanted to let you know it was the ALTERNATOR. Why, using 2 different scopes and other methods trying to narrow this down showed nothing concrete......i have no idea. The alt was definitely the noisiest off the belt driven components, but the whine / groaning noise didn't come up thru the scope(s) or metal pipes that myself and 3 other ppl tried.

I swapped the ALT out and the noise is gone. Completely gone.

Now that i've changed the ALT out, iv'e noticed the volt gauge slowly fluctuates at idle from roughly 11-1pm. When driving the needle is rock steady at 1215pm. Did some research and it seems this symptom is OK.

 

[xavierny25]

Now that i've changed the ALT out, iv'e noticed the volt gauge slowly fluctuates at idle from roughly 11-1pm. When driving the needle is rock steady at 1215pm. Did some research and it seems this symptom is OK.

I wouldn't trust that gauge your best bet is to keep an eye on it via a odb2 reader and car gauge pro or the equivalent.

 

[gladesteen]

Thanks X,

I will keep an eye on via my obd reader. From what i've researched as long as its not moving around while drving, this is pretty much "normal". Maybe i never noticed it before, but now that i was looking after i changed the ALT i saw it.

 

[thebat]

I just did this and lucked out, it was the idler pulley, a pretty easy fix. I could tell immediately when I spun the pulley after removing belt. I could hear the scratchy bearing noise loud and clear
I am still thinking of changing out the belt though. It only has about 30k miles but it measured out at about 2010 mm, I think it should be longer.
But, in the meantime, it is great having that whiny noise gone. Almost like a different truck!

 

[Maverick6587]

It only has about 30k miles but it measured out at about 2010 mm, I think it should be longer.
But, in the meantime, it is great having that whiny noise gone.

There are two different size belts depending on the model/year trailblazer you have. I would check with your local dealership and verify the length for your vehicle.

I was using the 2010 mm on my Saab for a year and ended up slowing burning up EVERY pulley that belt touched throughout that year or so. That was very expensive. I would just buy an ACDelco belt from the dealership. They're expensive from the dealership but, cheaper than replacing other engine accessories.

 

[Harpo]

I think the EXT models use the short belt because of a slightly smaller PS pulley.

 

[Maverick6587]

Oh, I did not know that. I did notice that on an alternator I bought, the pulley on that was larger as well. It was an aftermarket alternator and maybe they just put that size pulley on their alternator to fit more vehicles. The 2010 mm serpentine belt I had at the time would not even fit on it with the tensioner completely opened/down.

 

[thebat]

On Rock Auto, there are about a dozen belts for the TB LT listed. Many have the length in the "info" section. I see AC Delco for the TB LT is 2320 mm. The EXT is 2294 mm. I think this info is correct and I am going to replace my shorter belt the the 2320mm version.
BTW, there are a bunch of other belts listed with many different lengths. Some of them show the same belt for the base and the EXT. Be careful out there.

 

[XL Envoy]

Late recommendation as I was out of town about tracking bushings and bearings---

I know a screwdriver can conduct the sound over by the mastoid bone, but it is not always convenient to get the right position. Buy a stethoscope for the purpose. They are dirt cheap and keep you well out of all the spinning bits. No hair or sleeves to draw you into the action. The engine already knows what is happening, you do not have to "become one with it" to see what is going on.

Mine has 2 12" rod extensions so it can safely reach a good distance. Paid for itself the first time I was chasing what turned out to be a bad bushing. It was in the back of an alternator. You could reach the front with a screwdriver but on an older vehicle there can be enough noise traveling around to make it a "maybe/sorta/ I dunno/what is cheapest to try since I can't tell" type of guess. Listen to the front of the alt, you could hear something. Go to the back of it, and Bango. The slight increase of that particular whine was enough to pinpoint the issue.

This was long ago, and there was no way I could have reached it with a long screwdriver. Would have needed to remove the hood and hang in a sling. But with the stethoscope, it was definite immediately. And it was my only vehicle so I needed to get the right part from the jump.

So pop for the $10 or whatever. I have used it elsewhere. Pointed out a bad hot water circulator pump on a furnace and numerous other stuff over the years.
John S.

 

[Brian K]

I recently changed both tensioner bearings (took bearings out of the pulleys) and noise went away. I took the belt off and spun everything by hand until I felt a roughness. Also changed PS pump, water pump and belt at 160K miles - just because of mileage. I am considering just changing the alternator just because I don't want it to fail when I'm out somewhere. There are brushes, bearings and diodes in there so more to fail one day. Has anyone bought a repair kit for this alternator? PN's? Any brand recommendations? Is there a 'typical' mileage that folks have had theirs replaced?