Is my alternator going out?

[slow_c1500]

Hey all, I noticed today that my truck is making 2 new sounds:

1. Faint whining noise that I can only notice from inside the cab, seems like it’s coming from the radio area or transmission hump area. It gets higher pitched as RPM increases which immediately tells me it’s engine related. I also only notice this sound when I have radio on but volume turned all the way down. I turned the radio off and it went away, which leads me to believe that the noise is radio static caused by a worn alternator.

2. Faint rattling sound which I can only notice when revving by hand from the engine bay. Most noticeable when “deccelerating”

It is seeming to me like an alternator, but I’d like to hear some feedback. Thanks! Also it is a 96 5.7

 

[movietvet]

Check the charging system and post the output at idle with everything turned off and when things like blower motor and wipers and lights are on, under a load.

Post a video of the sound.

 

[Schurkey]

Connect voltmeter to alternator output terminal, and ground.

What is the DC voltage with the engine off?
What is the DC voltage with the engine running at fast idle, high-beam headlights, wipers, and so forth turned on?
What is the AC voltage with the engine running at fast idle, high-beam headlights, wipers, and so forth turned on?

If you have a current probe satisfactory for 100+ amperes, clamp it around the alternator output wire. What does the alternator produce for amperage with the engine running at fast idle, high-beam lights, wipers (fast), radio, dome light, A/C, and any other accessory you can think of, turned on?

You could remove the alternator and have it tested for free, off-the-car at most parts stores. Problem is, off-the-car testing is not a wholly-reliable method.

 

[99xcss4]

well this is just strange was just talking with a friend about alternators and he told me some thing that I had never heard of and have no idea if it is true or not any one ever hear that a screwdriver will stick to a good alternator and not stick to a bad I told him that it sounded like hog wash to me but shore enough tryed it with one that tested bad and it did not stick and it did stick to one that tested good at a parts store

 

[Schurkey]

Electromagnetism. More current produced = more magnetism.

 

[GoToGuy]

Basic science of electric generators, remember in science class. Oh wait, do they teach that anymore?

 

[someotherguy]

The whining through the stereo speakers can be noise from failed diode(s) in the alternator, but can also be a poor ground in the stereo wiring - especially if it's got an aftermarket unit, depending on how it's wired in, and whether or not there's aftermarket amplifiers in the mix.

Richard

 

[movietvet]

The magnetic field is created and the tip of screwdriver will be drawn right at the back center where the rear bearing cap area is. It will be magnetic because it is charging but it will not tell you how good a job it is doing until you test the system, like @Schurkey recommended.

 

[1998_K1500_Sub]

Hey all, I noticed today that my truck is making 2 new sounds:

You said “new sounds”.

Is anything else “new”, such as a recent change, ANY change, made to the vehicle… electrical OR mechanical?

Re: Alternator noise in the radio, this can be caused by a “poor or improper ground upon installation” of a new unit OR a “good ground gone bad” on an existing unit.

In the latter case, it’s possibly due to a failed or failing OE ground strap, but could be elsewhere.

 

[jd33173]

Put a voltmeter on the battery with nothing on just engine running, you should get over 14v. Turn on ac, etc you should get 13 something. If not, you have a charging issue (which COULD involve the battery but first things first). If you are concerned about rattling on decel, pull the belt off the alternator and give it a spin, if it does not spin VERY smoothly/ easily, internal bearings may be going and needs swapping before it grenades. This is not a great test for the bearings as many times the bearings dont really start failing unless they have some load on em from belt tension. While you have the belt off, may want to check any idler pulleys for the rattle.