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How do I tell? Battery or Alternator Going?


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18 replies to this topic

#1 EOppegaard

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Posted 17 August 2004 - 12:32 PM

Alright...I am having voltage drops every once in a while when I am putting a strain on the vehicle...i.e. radio, wipers, and AC. I am now averaging a voltage of only 11.8 volts. Every once in a while for some reason it peaks right on up, however usually averages around that when the car is in motion. When I stop though, the voltage can drop down to 9 volts :eek:

How can I tell if it is the battery...or the alternator going?

#2 slo5oh

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Posted 17 August 2004 - 01:05 PM

With the car running you should never see voltage below 13 to 14... unless you are powering a pair of 12" thumpers in your trunk... keep your radio off for the test. If it's the amp sucking all your juice then you need to buy a cap. aka capacitor.

If your voltage is low when engine is running it's your alt. If voltage is low when engine is off then it's your battery. But, if your alt. is going then your battery may not be fully charged. Test the voltage of battery when car is off. If it's below 12 (I think 12.8 is fully charged) and dropping, usually one one hundredth a second or 2... i.e. 11.85.... 11.84....... 11.83 then you have a bad battery but the alt. has been saving you up to this point.

If it's your battery I recommed Costco... their prices are always lower and at times half what pep-girls, and auto-bozone want...

#3 EOppegaard

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Posted 17 August 2004 - 01:10 PM

I think it is the alternator as well.

Any reccomendations on a replacement, as well as a shop to do it? I am in the Orlando Florida Region right now.

#4 MorganM

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Posted 17 August 2004 - 01:39 PM

Sounds like the alternator to me. Your voltage is dropping and spiking while the engine is running. Thats the alternator do'n funny things. The battery and alternator work together however so a lot of times if the alt is going the battery goes too and if the battery is going it over works the alt and it goes out.

A good battery tester will have a Load Test on it. That will tell you if the battery is good to go. As for alternators I've seen 3 different fancy devices and machines say an alternator was OK only to replace it and fix my electrical problems that I suspected was an alternator. This happend on 2 different alternators :(

If you got the money to spend do both. Do a load test and replace the alternator.

#5 EOppegaard

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Posted 17 August 2004 - 01:44 PM

Can a "load test" be done at like an advanced auto parts? Is that the battery cart thing I always see sitting in there?

#6 slo5oh

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Posted 17 August 2004 - 02:05 PM

I'm a "do it yourself" junkie... Save youself lots of money and do the repair yourself. Head out to a local junkyard and walk around looking at all the different alts. on the subies... I almost always see one that looks either new or newer. Otherwise most alts are the same. Call around to different car parts stores and price them out. Most of them will be rebuilds for $X + a core charge most with a "lifetime" warranty... but keep your receipt.

#7 EOppegaard

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Posted 17 August 2004 - 02:24 PM

yeah...one slight problem...I am on an internship in Florida until Jan...and I don't have tools, or a place to work down here!!!

#8 frag

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Posted 17 August 2004 - 02:47 PM

yeah...one slight problem...I am on an internship in Florida until Jan...and I don't have tools, or a place to work down here!!!

You can replace your alt with a 12 mm combination wrench (one box, one open) Maybe a 10 mm one to remove the belt guard and one of the connectors. You dont even need two wrenches cause every nut involved is so made it does'nt need to be held at the other end. Check the size of your bolts to be sure but I'm pretty certain you dont need more than one or two size wrenches.
Good luck!
P.-S. you might also check the price of an alternator at 1stSubaruparts, I bought one there (Subaru rebuilt) and it was not very expensive once you deduct what they give you back for the core.

#9 slo5oh

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Posted 17 August 2004 - 04:16 PM

This can be done in a parking lot, or behind a gas station... You will need a 10mm and and 12mm open end wrench. On second thought.. you may not need the 10mm, but when in doubt...

#10 MailManX

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Posted 17 August 2004 - 04:34 PM

If you don't mind non-Subaru aftermarket parts, I bought my last alternator at Autozone. It has a lifetime warranty, but that was two years ago and it's still working fine. I forget what I paid for it, but it wasn't much. And like the others said, I changed it myself in the parking lot in 10 minutes with two tools so I could take the core back into the store.

#11 EOppegaard

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Posted 17 August 2004 - 07:34 PM

Well this doesn't sound that hard at all...

Does anyone have specific instructions/steps on how to do this?

How about pictures...I know...I am greedy!

Also, what do I need to look for in buying an alternator? Obviously there needs to be a size/model/type I am looking for here. I also am interested in seeing if I can find a higher output alternator...however if not...the regular one would be fine!

Thanks guys for your help!

#12 SuperRallyRoo

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Posted 17 August 2004 - 11:50 PM

If you just look at it you will figure out how to do it. I just did this today the battery was killing my alternators I notice it runs with lower idle smoother idle and doesn't jump around as much. I need to wire up a volts gauge so I can see whats happening from now on. Theres basically a couple bolts holding on a cover that goes over the alt belt (and ac belt if there.) Then theres the bolt that holds the left part of it on with a little weird nut with prongs to grip the alt. On the left you have to loosen the tensoner by unscrewing it a bit then unbolt the bolt thats perpindicular to the radiator. All you need is 10 and 12mm sockets, or wrenchs. Take the belt off undo the 2 wire harnesses going to the alt. Pull it off, put in new one do the reverse. Hope this helps.

#13 jcniest5

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Posted 18 August 2004 - 02:14 AM

The alternator on the EJ22 (haven't seen other engine models yet) is one of the easiest parts to replace (IMHO). Based on the EJ22 engine, facing the engine, (you will need to remove the top protective sheets (don't know what they are called)), the alternator is in the middle, to your left is the power steering pump, in between them is the idler pulley you will need to loosen the front bolt so you can relief the belt tension by turning the top bolt (both 12mm socket) counterclockwise. Once you have loosened the pulley enough, slip the belt out, loosen the two bolts holding the alternator and pretty much just slide it out of its place. Of course, you will need to disconnect the two wire harness (connectors). Installation is just the opposite of what you've just done.

#14 Ranger83

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Posted 18 August 2004 - 04:15 AM

Alright...I am having voltage drops every once in a while when I am putting a strain on the vehicle...i.e. radio, wipers, and AC. I am now averaging a voltage of only 11.8 volts. Every once in a while for some reason it peaks right on up, however usually averages around that when the car is in motion. When I stop though, the voltage can drop down to 9 volts


Is it only the newer Legacys that had the Alternator recall? They would not charge at high engine speed, so people would drive down the highway, get low voltage readings, pull off, alternator would function normally, they'd get back on the highway, etc. We never experienced the symptoms but one friend did on a '98 OBW and a mechanic replaced the alternator. Subaru later reimbursed him.

You're the guy that had a radio and a bunch of emergency lights, right? Maybe now is the time to go to a higher output alternator. I thought you'd purchased an AGM battery, so it should still be on warranty?

#15 EOppegaard

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Posted 18 August 2004 - 08:21 AM

Yeah...I have a lot of crap in the car. I have the new battery, that's why I figured it was not this going, and also when I meter the battery, it is all good.

As far as a HO alternator, where can I get one that will fit? I imagine it's not something I can pick up at Autozone or Advanced auto Parts!

#16 EOppegaard

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Posted 18 August 2004 - 10:48 PM

So where do people reccomend getting an alternator from? I am looking for a high output model, that I can just bolt in. I am sure there is one made for it somewhere, however I just can't find it yet!

#17 Cougar

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Posted 21 August 2004 - 07:03 AM

I would check with a place that specializes in electrical repairs and parts about a new alternator. Before replacing it though I would first have them verify that yours is really bad before replacing it. You should also check all the connections to the battery and the alternator plus the belt tension if you have not done this already.

#18 jcniest5

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Posted 21 August 2004 - 04:40 PM

Another way to test if your alternator is working/charging properly is to start the engine and let it run while disconnecting the battery cable (positive). If your engine continues to operate without the battery, then alternator is still working. However, if your engine dies immediately after you disconnect the battery cable, your alternator is bad for sure and needs to be replaced or fixed. If you know how, alternator can be fixed, mostly it's just the two brushes inside it worn out. Get two new brushes and replaced the worn out brushes will fix the problem 95% of the time.

#19 EOppegaard

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Posted 29 August 2004 - 04:03 PM

Replaced the Alternator Today...all is well.

Thanks for the help guys!




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