Key On + Engine Off = Alternator Whine?!

[jmgtp]

Well the title pretty much says it all. When the key is in the "run" position but the engine is off the alternator makes a fairly high pitch whine. Well at least I think its the alternator, I poked around and even used a stethoscope and when I put it on the alt the sound became very loud and clear. So... this obvisouly isnt normal. BUT, if youve read my other posts, you would have noticed that my engine has ran like crap ever since I changed the plugs/wires, so bad that its not driveable (idles, starts, revs in neutral fine but no power at all)... I removed the alt when I changed the plugs/wires so I could access the rear bank easier. So... could I have messed something with the alt or wiring that would cause it to whine and the engine to not have any power (note: engine ran strong before plug/wire change/alt removal) ?? BTW while running the alt charges normal.

Help! Ive had the car for 2 months and drove it only for 1 week. I need this thing to run before snowfall. ECM shows no stored codes. All the obvious has been checked. 90 beretta GT 3.1

thanks!
-john

[3100 MPFI]

try unplugging the alt, and turn the key on (leave the battery connected, just pop out the electrical plug). See if it makes the noise. You might have a short in the alt.

[geoffinbc]

I'd say the rectifer is 1/3 or 2/3 dead. Pull the clip in plug see if the noise goes away. If it does you need a new alt. I had the same thing happen on my Sonoma

[jmgtp]

but either of those possible causes wouldnt be cause for the enormous lack of power?

update: went to car and removed harness. high pitched sound is gone. any ideas?


thanks for the responses,
-john

[3100 MPFI]

for lack of power, make sure that you do not have any spark plug wires crossed (I tend to do that ). Also, check your DIS and make sure that none of the coils are cracked (happened to me also). Make sure that you are not using any spark plugs made by bosch.

I also recommend replacing the alternator.

Plugged in = noise.
Unplugged = no noise.
solution = BAD (or getting that way) alt.

[jmgtp]

for lack of power, make sure that you do not have any spark plug wires crossed (I tend to do that ). Also, check your DIS and make sure that none of the coils are cracked (happened to me also). Make sure that you are not using any spark plugs made by bosch.

I also recommend replacing the alternator.

Plugged in = noise.
Unplugged = no noise.
solution = BAD (or getting that way) alt.

Ive checked and rechecked spark plug wire routing so many times I've lost count. Plugs are rapid fire 6s gapped properly. I've tried 3 different ignition modules (each with 3 diff coil packs on them), currently the known good module and coil packs (taken from my running dohc) are in the 3.1 and the 3.1 module and coils in the dohc (and the dohc runs fine with them). I'm going to run the car for a minute with the accessory belt off to make sure that the alt isnt somehow creating an electrical problem causing my huge loss in power. Otherwise I'm at a loss on whats causing it

thanks again,
-john

[geoffinbc]

You are having drivability problems because the alternator has a bad rectifier and it it now puting out AC voltage and alot less current than it is suposed to be. You will still be getting 14V but it is not capable of putting out the current it needs to be.

Change your alternator or find the same model from any vehicle and change the rectifier. Takes 20mins I did it to my truck. Took the guts from a 1995 Camaro alt left over from my swap and put it in the case for my truck.

When my alt was like yours I also had a slightly goofy idle and flickering lights at low idle.

[jmgtp]

You are having drivability problems because the alternator has a bad rectifier and it it now puting out AC voltage and alot less current than it is suposed to be. You will still be getting 14V but it is not capable of putting out the current it needs to be.

Change your alternator or find the same model from any vehicle and change the rectifier. Takes 20mins I did it to my truck. Took the guts from a 1995 Camaro alt left over from my swap and put it in the case for my truck.

When my alt was like yours I also had a slightly goofy idle and flickering lights at low idle.

Sounds like a possibility... but I have run my dohc with no accessory belt (which means no alt) for minute (on a test run down the driveway) and it had all its power. I ran the 3.1 (on a battery that had been charged overnight) with the harness unplugged and serpentine belt off and still no power. Althought the alt does seem bad (from the sound) I can't justify replacing it until the engine runs right... this is of course assuming that the alt isnt the cause of the problem in the first place, which I dont truely believe it is

[Anonymous]

Go buy a new alt, replace it, see if thats the problem. If not, return it. I would that at this point you'd be willing to try anything.

[geoffinbc]

If it is whining the rectifier is bad. Take a look at it. Remove the little plastic cover that covers the soldered connection between the rectifier and the case windings. Do you see any heat marks? It will look like white gray or black poweder sitting on the rectifier, wires or case. This will be a sure sighn the rectifier is toast. It could also have burned up a diode internaly and there will be no sighn of heat.

Do another test hook up a multimeter and test for AC voltage. See what happens.

[Cliff8928]

... My alt makes a faint high-pitched whine with the Key On Engine Off... Always has.. the old CS130 and the new CS130-D

Cliff Scott
89 BerettaGT
89 Volvo740

[farmerz24]

normally the alt will whine when the exciter wire is connected. if it is whining when the key is off power is getting to it somehow.