Thread: Alternator Whine when car off.

EDIT: Solved - see post dated Nov 14, 2014.


Hi guys,

Car: 2000 GTP

So something has been killing my battery when I let it sit overnight, and I think its my alternator.

When I turn the car off with the battery connected, I get a periodic low electrical hum/whine from the alternator. This noise sequence is thus: low hum for 2 seconds then off for 2 seconds, then hum again for 2 seconds then stops, etc.

Any idea on if/how I can test this? Read somewhere that the 'field' part of the alternator might still be powered once the car is turned off, and this could be causing the battery drain, but I'm nor well versed enough with electrical knowledge to test this.

Thanks.

PS. Mods, if this is the wrong section, let me know and I'll move it.

drive a parts store, have the alt and battery tested.

if you have avolt meter, car off test the batery, you want to see 12 volts at least.

car on test the battery again, you want to see over 13 volts now, up to 14.

Unhook the alternator overnight and see what happens if the battery doesn't drain there's your problem. Using a volt meter to test battery voltage won't really tell you anything beside if you sit there and watch it for a couple of hours you might be able to watch it drain. You could use the voltmeter to check and see if anything is pulling any unreasonable voltage while the car is off by testing wires individually

Scottydoggs: checked the battery and alt - they check out ok per your criteria. 12.7v on the battery when car off, and 13.4 or something with the car running. Alternator bench tested ok too.

Blowngp: to unhook the alternator, do I just remove the two-wire harness? Its a 4 pin plug but only 2 wires go into it. Or should I remove all the alternator plugs/wires like the big red one too?

Thanks to both of you for your help. I'm hoping I can sort this sucker out. It was working fine and I've followed some other instructions regarding testing for other sources of current draw but can't find anything else. I only heard this alternator noise by chance and it stopped once I disconnected the battery.

taking that thick cable off the alt, and un plugging the flat plug should do it.


edit: the alt could have a bad voltage regulator. unplugging it will test that. if its good int he moring the alt is bad.

Good man!

Right then that's what I'll do. I'll update this thread in the morning.

Cheers mate!

OK so I unhooked the alternator as suggested, and I'll check tomorrow.

One thing I wanted to talk about was then when I re-connected the battery, I checked the voltage going to the alternator plug.


Pin B was receiving 12+v on it once the battery was connected.

I don't know if that's normal or not, and maybe that's why my alternator is receiving power and making the noise too?

If anyone has a clue whether this is supposed to be powered once the battery is connected, pop in .

no clue on the diagram.

but ive got the same issue im dealing with on a commercial lawn mower, battery dies over night. was told by the starter and alt re builder to unplug the voltage regulator when it sits over night. if the battery is still charged in the morning the v/r is bad.


i just got it all back together the other day with a fresh charge, everything hooked up, the battery was dead 2 days later, so i need to charge and unplug the v/r to see if thats my parasitic draw.

Originally Posted by Scottydoggs

no clue on the diagram.

but ive got the same issue im dealing with on a commercial lawn mower, battery dies over night. was told by the starter and alt re builder to unplug the voltage regulator when it sits over night. if the battery is still charged in the morning the v/r is bad.


i just got it all back together the other day with a fresh charge, everything hooked up, the battery was dead 2 days later, so i need to charge and unplug the v/r to see if thats my parasitic draw.

Have you tested the battery?

UPDATE:

Scotty/blowngp: So I started it up my car this morning and it starts up fine. So it definitely looks like the alternator/voltage regulator is kaput.

I don't know if there's a way to replace only the voltage regulator, but I guess I'll pull it off and have a look. Thanks for all your help with this guys!

Scotty, Good luck with the lawnmower. Hope you find it to be a cheap and easy fix!

Yeah battery was holding at the same voltage as last night - 12.46v.

Edit: until I started it on battery and turned it off after 29 seconds - then it bacame 12.22v.

Originally Posted by Panzer4

Yeah battery was holding at the same voltage as last night - 12.46v.

Edit: until I started it on battery and turned it off after 29 seconds - then it bacame 12.22v.

That seems normal

So we both agree its the alternator then?

edit: voltage regulator in the alternator?

That'd be what I'd try

Only way to replace parts in it is to bring it to a alt/starter shop or learn how on your own. I'd bring it to a shop.

i looked into rebuilding my own alt, the rebuild kit is like 35 bucks. but, you need a press to to even get close to working on it. no press to use, take it to a re builder. cause you'll never open it all up.

I'm taking it to a good alternator shop tomorrow. I was doing some reading about how a bad diode can cause a parasitic drain.

Will update you guys once I find out. This has been one of the most curious problems I've had with this car!

Hm. That is neat. I'd just throw a JY alt in lol