Real-time Christmas help needed: second alternator died in two months, keep blowing diodes (2 Viewers)

[Eicca]

Two months ago the alternator in my parents’ 1999 started making a weird whirring/moaning noise, and about two days later stopped charging.

Replaced it with a reman unit from my local dealer.

This week that unit started making the exact same noise. It’s still charging at the moment but the electrical system feels week and if we keep driving this we’ll almost certainly have complete failure very shortly.

I’ve gotten crap remans before but they’ve always just not worked at all upon install. Never have I experienced an alternator making this noise, never mind two in a row.

What could the noise possibly be, and what external factor could cause it? It ain’t the battery as we put in a brand new on with the reman alternator. Bearings are also ruled out. It’s also not power steering fluid as the new unit had a shield over it.

At a loss, and need to figure this out quick. Your help is much appreciated.

EDIT: Finally managed to get the increasingly-useless Google to tell me that diode failure is the cause of the whining. So now, why would the car be blowing diodes repeatedly?

Here’s a video of the whirring/moaning noise (identical in both units):

 

[Trapper50cal]

So, I don't know if this will apply but we had an issue with our '08 Forester where we kept frying alternators and it had to do with a corroded lead. Apparently what was happening was that the alternator was tricked into thinking it needed to charge at it's highest level because it thought the battery needed more than it actually did, thereby either frying the alternator from being constantly at max output OR frying the battery due to overcharging. Then, if the battery was dead, the alternator continued to have max output requested and would then fail from the same issue.

All that to say, make sure all the leads between the two are free from corrosion and that all the "communication" between the two is unimpeded.

And make sure that the battery is good and not always requiring max output from the alternator.

 

[Eicca]

So, I don't know if this will apply but we had an issue with our '08 Forester where we kept frying alternators and it had to do with a corroded lead. Apparently what was happening was that the alternator was tricked into thinking it needed to charge at it's highest level because it thought the battery needed more than it actually did, thereby either frying the alternator from being constantly at max output OR frying the battery due to overcharging. Then, if the battery was dead, the alternator continued to have max output requested and would then fail from the same issue.

All that to say, make sure all the leads between the two are free from corrosion and that all the "communication" between the two is unimpeded.

And make sure that the battery is good and not always requiring max output from the alternator.

Hugely helpful. I’ll check all the connections right away.

Luckily I know the alternator side of the positive lead is clean cuz I just saw it…

 

[Trapper50cal]

How tight is the belt?

 

[Eicca]

How tight is the belt?

Whatever the tensioner sets it to.

 

[Trapper50cal]

Could part of the noise be a failing idler pulley? I'm just spitballin'

 

[2001LC]

So second has not failed, you just fear it will based on sound.

Short is possible, as is a bad reman. So is weak belt or belt tensioner or failing pulley bearings. A mechanics stethoscope, can help isolate sound.

One thing, I've notice. Alternators don't last long, if #1 skid missing.

You mention "not power steering fluid as the new unit had a shield over it". Don't count on shield keeping out leaks from PS. Correct leak!.

 

[Eicca]

Could part of the noise be a failing idler pulley? I'm just spitballin'

I checked them all with a stethoscope, totally fine. The noise went completely away when the reman was installed and the car stayed quiet until this weekend.

 

[Trapper50cal]

Well, that's pretty definitive.

 

[Eicca]

So, I don't know if this will apply but we had an issue with our '08 Forester where we kept frying alternators and it had to do with a corroded lead. Apparently what was happening was that the alternator was tricked into thinking it needed to charge at it's highest level because it thought the battery needed more than it actually did, thereby either frying the alternator from being constantly at max output OR frying the battery due to overcharging. Then, if the battery was dead, the alternator continued to have max output requested and would then fail from the same issue.

All that to say, make sure all the leads between the two are free from corrosion and that all the "communication" between the two is unimpeded.

And make sure that the battery is good and not always requiring max output from the alternator.

Well we seem to be on the right track. The positive terminal of this brand new battery was already covered in that blue powder stuff, and the terminal itself tore apart when I tried to loosen it. That fuse box is also full of grime.

Gonna replace the terminal, clean the crap out of all contacts, and I’m also going to replace the 140A ALT fuse. Hopefully that rectifies the issue.

 

[Eicca]

The smoking gun has been found.

The ALT-S circuit, which tells the alternator how much charge the battery needs, goes from the battery, through the 7.5A ALT-S fuse, through junction EE1 (right behind the battery) and to the alternator plug.

Between the ALT-S fuse output terminal and the female pin of junction EE1 is reading 3.4 MEGA-ohms.

(Male pins to alternator plug is perfect continuity.)

There’s so much resistance that my non-auto-ranging multimeter just sees an open circuit. But my nicer meter sees that massive resistance in the wire. So the alternators were thinking the battery was nearly empty and trying to charge full blast the whole time.

Now I just have to figure out how to fix that wire…

 

[Eyedaho]

I'm glad you found the issue! Hopefully you can find a replacement fuse block.

 

[Eicca]

I'm glad you found the issue! Hopefully you can find a replacement fuse block.

Speaking of which, an update: I missed a part in the diagram where that ALT-S circuit passes through junction connectors 1J and 1M on the bottom of the main fuse block.

So gotta isolate the problem further. Hopefully pulling the fuse block isn’t a PITA.

 

[2001LC]

You speaking about box hanging off battery positive post

 

[Eicca]

You speaking about box hanging off battery positive post

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No I need to remove the main fuse block. And right now I cannot figure out how.

 

[Eicca]

Actually wait. I should remove and test the battery fuse box first since it’s much easier.

I’m gonna do that.

 

[Eicca]

Bingo. Perfect continuity from the ALT-S fuse wire to junction EE1. The culprit appears to be lousy fuse contacts in that battery fuse box.

Initially I wasn’t getting continuity on the side of the fuse contact that is actually attached to the wire, but I was reading 3.4 mega-ohms on the other side, which means the continuity was coming from the grease that’s all over this fuse block.

 

[Eicca]

Weeeelllll nothing is quite as fun as discovering your senile brain was probing the wrong wires the whole time.

Sigh.

So the only kinda-smoky gun was the original positive terminal clamp falling apart.

But at least that circuit has been thoroughly tested and I know for a fact that’s all good (and probably was the whole time).

 

[Eyedaho]

Weeeelllll nothing is quite as fun as discovering your senile brain was probing the wrong wires the whole time.

Sigh.

So the only kinda-smoky gun was the original positive terminal clamp falling apart.

But at least that circuit has been thoroughly tested and I know for a fact that’s all good (and probably was the whole time).

That clamp definitely could be the root cause though!

 

[Trapper50cal]

Seems like it would still be a good idea to do what's depicted in 2001LC's post above. I know I'm going to look at mine...
Well, I'm adding military post clamps when I mount the winch so that'll be dovetailed in there...

But yeah bad clamp needs to be solid.