Is my alternator going out?

[df2x4]

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

One of my dad's earlier 400s did this straight from the factory when it was new. Very slight alternator whine through the stereo when it was powered on. Seemed to be most noticeable when playing a cassette IIRC. He had it fixed under warranty but unfortunately I don't remember what the cause was... I'd bet on a ground issue though.

 

[slow_c1500]

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.

It has an aftermarket radio but that has been installed for about 2 years. I’ve changed the fuel pump, and I switched the taillights, third brake light, and turn signals back to oem halogen from LED. Not sure if any of these could possibly be related.

 

[1998_K1500_Sub]

It has an aftermarket radio but that has been installed for about 2 years.

OK, so you've had no "whine" noise until recently... "new", as you said.

I could tell you how to check the alternator with an oscilloscope, but I'm guessing you don't have access to one.

Personally here's what I would try:

Disconnect the alternator plug (probably looks like this below) and see if the whine goes away. If so, it means the whine's somehow related to the alternator... at which point I would probably swap the alternator with another to see if the whine disappeared.

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Meanwhile, @jd33173 gave you some good suggestions for alternator and/or belt-related noises. The noise you're hearing MAY be something other than these, of course.

I’ve changed the fuel pump, and I switched the taillights, third brake light, and turn signals back to oem halogen from LED. Not sure if any of these could possibly be related.

I wouldn't expect these to cause a whine. However...

When you changed the fuel pump did you confirm the condition of its ground wire? I have a Suburban, and my pump grounds to the frame in the rear. On the pickups, I assume the pump grounds on the frame as well but I'm not certain of the location.

I'm not saying this is related to the whine, I'm saying it's worth checking

 

[slow_c1500]

I tried unplugging the alternator and the radio whine went away. Also when i turned the alternator by hand with belt removed, it squeaked a little bit. It’s hard to describe how easily it spun, I can do it with one finger but it didn’t spin SUPER easily.

 

[1998_K1500_Sub]

I tried unplugging the alternator and the radio whine went away.

So with the engine running (ignition system operating), alt disabled, the whine is gone, yes?

Also when i turned the alternator by hand with belt removed, it squeaked a little bit. It’s hard to describe how easily it spun, I can do it with one finger but it didn’t spin SUPER easily.

Did it rotate smoothly through multiple rotations? E.G., place your fingertip on the pulley and rotate it with the tip constantly against the pulley so as to sense any variation in drag or lack of smooth rotation.

Did you check other areas for noise as @jd33173 suggested?

 

[GoToGuy]

As mentioned in earlier, I have had to move common gang grounds when feedback was heard from speakers. Why? No idea, but it solved a detectable noise. Just one of those electric gremlins.

 

[jd33173]

Alternators are not forever, i made a living fixing broken ones until discount auto parts destroyed the industry with "lifetime warranties" ( which guaranteed you would be swapping their crappy alternators every 18 months for the rest of your life). Time for it to go. If its the original cs maybe take the opp to upgrade to the ad244 or just another nice cs130 (up to u and your budget and vision for your truck).

 

[slow_c1500]

Yes, engine running with alt unplugged got rid of the radio whine. I will check later about the smoothness of the pulley's rotation.

Also i took her for a drive today and she started up fine after sitting for a few days. But when i tried to start her again after sitting for maybe 15min, it cranked very briefly before suddenly stopping. No electronics were coming on in the KOEO position. Tried again shortly after and it fired right up with electronics coming on with KOEO. It did a similar thing a couple days ago. Really weird, it acts like the battery died but then it changes its mind and lets you crank right after. Only does this after sitting for a short while. Could this be related to my potential alternator troubles?

Also not sure if this is related but a few days before those events, there was an instance where it would only start when i gave it throttle, and it would die when i put it into gear. Well, it died in gear the first two tries, thankfully on the third try it didnt die but still needed some throttle to fire up. Hella confusing cause it has only done this once. Every other time Ive started it, before and after this, it didnt need throttle and didnt die in gear.

 

[Schurkey]

she started up fine after sitting for a few days. But when i tried to start her again after sitting for maybe 15min, it cranked very briefly before suddenly stopping. No electronics were coming on in the KOEO position. Tried again shortly after and it fired right up with electronics coming on with KOEO. It did a similar thing a couple days ago.

1. Loose connection--battery cable at battery, battery cable at starter, battery cable where it's attached to block, etc.

2. Failing ignition switch

 

[1998_K1500_Sub]

Yes, engine running with alt unplugged got rid of the radio whine.

Check your battery connections and IGN switch as @Schurkey suggests. Once those are known to be good, return to solving the whine problem. They might be interrelated.

Assuming the whine still remains, I would swap alternators.