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Old 06-02-2008, 12:19 PM   #1
rudemood12
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Default Weird voltages - alternator problem?

been having an issue with my '02 WRX (no mods) for a while now, but I finally decided to make a post about it to try and get some info.

my car has a gauge cluster, so i've noticed that after the car has been running for a while, when it comes to an idle (at say, a red light), the voltage will slowly drop from 14vish to anywhere around 12v (sometimes lower), then as soon as you hit the gas, it will head right back up to 13.5-14v. turning on the AC will drive it a bit more batty.

the reason it bugs me now, is that the car seems to stumble a bit when it gets low, whereas leading up to this, it didnt do that.

my feeling is that it may be the alternator, but i was told when i bought the car that it had been replaced once already. battery has been replaced as well, i believe.

some notes on the last oil change i had done mentioned that the battery terminals needed to be cleaned, so i wasnt sure if maybe it had something to do with that. another note - when i had it inspected, they were unable to connect the OBD machine to communicate with the computer. they mentioned it might be a bad ground or something. related at all?

any information you guys could provide would be appreciated. thanks!
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Old 06-02-2008, 01:08 PM   #2
rkramer
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so... clean the battery terminals. bad terminals will cause all kinds of electrical gremlins, as well as possibly destroying your alternator and/or ECU if they are REALLY bad.
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Old 06-02-2008, 01:15 PM   #3
rudemood12
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ooh. thanks for the heads up. i will definitely do that.
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Old 06-02-2008, 03:12 PM   #4
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sounds like corrosion or bad voltage regulator in your alternator. I guess it could also be a ****ed up winding or diode.

try doing a voltage drop test, with the car running check voltage from alternator post to battery + terminal should be less than ~.3V same goes for alternator case to - battery terminal.
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Old 06-06-2008, 07:12 PM   #5
reaper447
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speaking of alternator i got a system in my 07 impreza and i was thinking of adding more stuff so to speak any 1 kno where i can find some with high output ?
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Old 06-06-2008, 08:56 PM   #6
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I suggest you get the alternator tested along with the battery. The alternator may have some diodes out and this would prevent the unit to put out full capacity. Cleaning the battery connections with a battery post cleaning brush is a good idea. Make sure the belt is snug also.
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Old 06-07-2008, 12:03 AM   #7
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Quote:
Originally Posted by Cougar4 View Post
I suggest you get the alternator tested along with the battery. The alternator may have some diodes out and this would prevent the unit to put out full capacity. Cleaning the battery connections with a battery post cleaning brush is a good idea. Make sure the belt is snug also.
or even easier and very effective mix some baking powder with a little bit of water so its like brown goopy paste and spread it all over the terminals spray clean with a hose and repeat! when done, and youll know when your done, apply some battery terminal protector aka silicone.
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Old 06-08-2008, 03:58 PM   #8
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This is the only one that I could find but it says it for the '05-'02 IMPREZA WRX 2.0L but it also says that it will work on the '06-'99 ALL FORESTER AND LEGACY 2.5L so it may work on the 07 I would check your connector against someone with an 02-05 and see if they are the same.

http://www.maniacelectricmotors.com/11058hiamp.html
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Old 06-08-2008, 05:35 PM   #9
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After the car is started the battery is not running the car. I would make sure you don't have tune up issues as it sounds like a low idle issue to me. Yet you didn't say what the idle is at.
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Old 07-19-2008, 09:43 PM   #10
rudemood12
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just to update this a bit - i had a tune up done (spark plugs, air filter, fuel filter, oil change, battery terminal cleanup) and still have the same issue. i had them test the alternator while I was there and the printout I have shows that the alternator is charging in the 'low' range. they explained that it was still within an OK range, but bring it back in 2 months or so and have them re-check it.

its gotten to the point where I don't enjoy driving it. i cannot run the AC while not under throttle, otherwise the idle gets all funny and gets to the point where it almost dies. without the Volt gauge, I'd think it was an idle issue, but as soon as the AC clicks on, the reading starts to go crazy.

is there anything else I can have them check to see if its NOT the alternator? According to the records I received when I purchased the car, the alternator has already been replaced once.
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Old 07-21-2008, 11:47 AM   #11
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The alternator sounds like may be having some trouble after it has heated up. If you can tell me what some voltages are while the trouble is occurring I could tell you if that is the cse or not.

Get a digital voltmeter and check the DC and AC voltages at idle while the trouble is going on. Let me know what the results are.
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Old 07-23-2008, 07:54 PM   #12
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without checking, I can tell you that it will get as low as 12v on idle. as the problem gets worse, it will slowly creep from 14v back to around 12v, then back up under throttle. Even under throttle, with the AC on, it will struggle to get to 14v.

I'll see if I can get some actual readings though.
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Old 07-24-2008, 12:40 AM   #13
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It sounds like some of the diodes in the alternator have failed. You could have a load test done to see if that is correct.
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Old 07-26-2008, 07:59 PM   #14
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are there any recommendations for a good replacement? or are they all pretty much the same? what is required for removal/installation?
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Old 07-26-2008, 08:15 PM   #15
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I would recommend getting one that has a lifetime warranty, that way you are covered if something happens to it later on. They are usually pretty easy to remove and it doesn't require much more than a few basic tools to remove it. Be sure to disconnect the negative battery connection before working on the alternator. The main lead is hot to the battery so it will short if it touches ground without the battery cable removed. After the new one is installed and all connections are put back then reconnect the battery cable.
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Old 07-26-2008, 08:41 PM   #16
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I've been having similar issues as well. Today I cleaned my terminals and grounding spots. I added a big fat wire from te negative terminal to the fender wall and another one from the alternator main lead to the positive terminal, kinda like the "Big Three." Still dipped to 11.8 with my AC on full blast and my lights on. I was thinking of upgrading to a 140A alternator I've seen a few guys running here.

Last edited by Rodwrx23; 07-26-2008 at 09:35 PM.
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Old 07-27-2008, 02:08 AM   #17
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Quote:
Originally Posted by Rodwrx23 View Post
I've been having similar issues as well. Today I cleaned my terminals and grounding spots. I added a big fat wire from te negative terminal to the fender wall and another one from the alternator main lead to the positive terminal, kinda like the "Big Three." Still dipped to 11.8 with my AC on full blast and my lights on. I was thinking of upgrading to a 140A alternator I've seen a few guys running here.
I recommend you either remove the lead to the alternator that you added or install a in-line fuse near the battery. If the alternator develops an internal short you have no protection and you will have a lot smoke and a possible fire very quickly if that happens. The original lead is really all you need for things to work as they should and keep the battery charged.

Since the alternator isn't handling the load some of the diodes are most likely bad. Have the battery checked also to see if it is ok.
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Old 07-27-2008, 08:37 AM   #18
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Thanks for responding. I was hoping you wouldn't say that. I think my battery is fine becuase it's only like 6 months old and I'm seeing the same values as before I swapped it (I have a Braille on there now.) Looks like I'll be upgrading the alernator after I pay off my replacing my front wheel bearings. Thanks again.
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Old 07-27-2008, 03:23 PM   #19
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Quote:
Originally Posted by Rodwrx23 View Post
Thanks for responding. I was hoping you wouldn't say that. I think my battery is fine becuase it's only like 6 months old and I'm seeing the same values as before I swapped it (I have a Braille on there now.) Looks like I'll be upgrading the alernator after I pay off my replacing my front wheel bearings. Thanks again.
You're welcome for the help. Unless you have added some extra high current demanding accessories the normal unit should be fine.
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Old 07-27-2008, 03:35 PM   #20
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I've added a pair of 6.5" speakers on my rear deck and an amp running them along with my front door speakers. I'm seriously electrically challenged so I don't know if my HID morrettes have any significant additional load on the system as well. I figured since my diodes seem to be going bad, $163 for a HO alternator wouldn't be too bad of an investment vs. $201.06 for a stock replacement through a dealer.
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Old 07-27-2008, 04:00 PM   #21
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Well I guess the choice is pretty obvious. Hopefully the new unit will come with a lifetime warranty.
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Old 07-28-2008, 11:31 PM   #22
rudemood12
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cougar, thanks for all your input. one last question - i did a quick google search for some alternators and didnt really come up with anything. can you recommend a brand or website to purchase from?
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Old 07-28-2008, 11:54 PM   #23
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I don't have any suggestions for you but I recommend you just find a good local place that you can take the unit back to if something happens to it. Make sure it comes with a lifetime warranty. You may pay a little more than internet prices but over the lifetime it won't make much difference and you don't have to worry about shipping it somewhere if something happens.
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