Electrical Problems... Bad Battery or Alternator?

[jcaroth]

Hey everyone. After the success of my last post about problems after a timing belt change (due to a cracked radiator), I figured I'd start a new thread about my latest set of issues with the car.

 

Since replacing my timing belt, waterpump, and radiator, the car has been up and running for about a week. Since then, some issues have appeared:

• Rough idle/stuttering issue
  
• Flickering radio/HVAC controls
  
• Brake and battery lights flickering while idling at red lights
  
• Dimming headlights whenever I turn the AC on, plug something into my cig lighter, etc.
  

 

I've had some issues with my battery since purchasing the car last October, so my first instinct is to replace it. That said, I've done some reading up on the forums here and learned that the alternator could also be to blame. I logged the "Control Module Voltage" from the Torque Pro app (graph attached), and it looks like I'm floating right around 13.6 V while driving. With the engine stopped, the voltage settles around 12.5 V.

 

Two questions:

1. Does this look like a bad battery or a bad alternator?
   
2. Could this be causing the rough idle I've been feeling?
   

 

I appreciate the help.

 

EDIT: It's also worth noting that I noticed a torn grounding cable on the bottom of my engine, driver's side. I can replace this with regular 12 GA wire, right?

[apexi]

I kinda think that torn ground could be causing your issues. If it looks like the driver side ground on my NA, I'm not sure what the copper equivalent would be. I know it's easier to get copper, but for $8 I'd probably just go oem..

 

http://parts.subaru.com/a/Subaru_2008_Legacy25L-TURBO-5AT-4WDGT-Limited-Sedan/_52016_6023012/CORD-ANOTHER/B13-818-01.html

 

*I understand if you want to diy the ground, especially if you already have spare cable. Here's a thread where it's discussed a little.

 

http://legacygt.com/forums/showthread.php/ground-straps-bottom-engine-206442.html?p=4454860

[Max Capacity]

Replace both bottom ground wires. NAPA has some nice ground cables for around $10.

 

Clean and tighten both battery cables.

 

Have you cleaned the MAF sensor with a couple short spray's from a can of MAF cleaner ?

[sunny5280]

12.5V unloaded is a little on the low side. Ground strap is a possibility and for $8.00 is an inexpensive replacement. Here in Denver several auto parts stores will test both the battery and alternator at no cost.

[jcaroth]

Replace both bottom ground wires. NAPA has some nice ground cables for around $10.

 

Clean and tighten both battery cables.

 

Have you cleaned the MAF sensor with a couple short spray's from a can of MAF cleaner ?

 

I picked up some CRC electronics cleaner and some Chemtool B-12 to clean the MAF and the fuel system, hopefully those will help. Seems like the smartest next step will be to replace the ground straps, so I'll pick up some replacements tonight.

 

If problems persist, how can I figure out if the battery or alternator are bad? Should I just have them tested at the part store?

[gkinslow]

Have them both tested at an auto parts store you trust.

 

Takes away the guess work.

[jcaroth]

So I replaced the battery, cleaned the MAF, and installed a new grounding cable but the electrical problems haven't gone away. I tested the alternator by removing a battery lead with the engine running. The car did not stall out, which should suggest the alt is fine right? The parts store I visited today wasn't able to test it so I'm unsure. Are there other tests I can run? What else could be causing the drop in voltage and rough idle?

[apexi]

This is a little over my head, but I'm just curious about something. Is the negative cable tightly attached to the battery?

 

When I first replaced my battery with an aftermarket one, the negative terminal wouldn't fit tightly on the aftermarket battery. There was some sort of plastic ring built into the negative cable that prevented it from tightening down enough. Removed the plastic ring from the negative cable, and was able to get it to tighten down properly on the negative post. I'm the original owner of my car too, I guess subaru probably put it in there to prevent overtightening or something.

[jcaroth]

This is a little over my head, but I'm just curious about something. Is the negative cable tightly attached to the battery?

 

When I first replaced my battery with an aftermarket one, the negative terminal wouldn't fit tightly on the aftermarket battery. There was some sort of plastic ring built into the negative cable that prevented it from tightening down enough. Removed the plastic ring from the negative cable, and was able to get it to tighten down properly on the negative post. I'm the original owner of my car too, I guess subaru probably put it in there to prevent overtightening or something.

 

Yeah, it's on there good and tight. I made sure to roughen up the new terminals and coated it with battery terminal spray as well.

[Marvick08GT]

I am not sure why you would replace the battery. A faulty ground would not cause the voltage to be low at idle. That is caused by worn windings and brushes inside the alternator. If it was a ground issue the voltage would not go up with rpms.

 

Cliff Notes - Buy an alternator..

[08SpecB_DE]

I am not sure why you would replace the battery. A faulty ground would not cause the voltage to be low at idle. That is caused by worn windings and brushes inside the alternator. If it was a ground issue the voltage would not go up with rpms.

 

Cliff Notes - Buy an alternator..

 

What he said ^^^ Battery voltage at idle indicates the alternator is not charging.

[jcaroth]

Well... damn. I went to a local parts store that I've had good luck with in the past, but they weren't able to bench test the alternator in store. They advised me to start the car then unplug the battery. If the car kept running fine, they said, then the alternator was fine. I did the test and the car ran as normal, so I bought a new battery.

 

The old battery was ancient and leaking, so I'm not too upset about spending the money to replace it, but I'd like to be better informed before throwing more money at this issue.

 

How else can I test the alternator to make sure it's faulty?

[MilesA]

Well... damn. I went to a local parts store that I've had good luck with in the past, but they weren't able to bench test the alternator in store...How else can I test the alternator to make sure it's faulty?

I saw that using Torque you observed 12.5V with the engine stopped and 13.6V with the engine running. Those values are pretty normal.

 

But your problem seems to occur when there is some stress on the electrical system.

 

Do you have a multi-meter? I like to use a piece of independent test equipment rather than relying on some built in sensors & apps.

 

Set the multi-meter to measure DC volts. Observe what happens when the engine is running and headlights & fog lights are turned on, brake lights on, air conditioning running full blast, car stereo on, etc. Voltage should remain steady. If it drops, suspect a bad alternator and/or voltage regulator (built in to alternator). Another possibility is loose or corroded cabling. Try wiggling the cabling to the alternator while doing the stress test, see if you see any change.

 

Just some suggestions.

[08SpecB_DE]

I saw that using Torque you observed 12.5V with the engine stopped and 13.6V with the engine running. Those values are pretty normal.

 

But your problem seems to occur when there is some stress on the electrical system.

 

Do you have a multi-meter? I like to use a piece of independent test equipment rather than relying on some built in sensors & apps.

 

Set the multi-meter to measure DC volts. Observe what happens when the engine is running and headlights & fog lights are turned on, brake lights on, air conditioning running full blast, car stereo on, etc. Voltage should remain steady. If it drops, suspect a bad alternator and/or voltage regulator (built in to alternator). Another possibility is loose or corroded cabling. Try wiggling the cabling to the alternator while doing the stress test, see if you see any change.

 

Just some suggestions.

 

12.5V is not normal for an idling vehicle with no loads. He should have ~13.7-14.2V with or without loads.

 

Disconnecting the battery while the car is running is an old school method so I advise you don't try that too often. Like Miles recommended, use a multimeter at the battery posts and check voltage with no loads and then check it with multiple loads. If the torque app is an accurate tool, I'd bypass that test and go get a new alternator.

[MilesA]

12.5V is not normal for an idling vehicle with no loads. He should have ~13.7-14.2V with or without loads.

 

I logged the "Control Module Voltage" from the Torque Pro app (graph attached), and it looks like I'm floating right around 13.6 V while driving. With the engine stopped, the voltage settles around 12.5 V.

If you read carefully what jcaroth wrote above, he saw 12.5V when the engine was stopped and 13.6V when driving.

 

13.6V is what I have personally measured on my car. So, it seems normal enough based on my experience with the Legacy GT.

 

It seems reasonable to test the system under load, since that is where the problem is occurring. That is why I suggested that. Again, reasonable.

[08SpecB_DE]

I thought he meant engine idling but that's where my tech mind went

 

Make these recordings:

 

Engine idling, no loads -

Rev to ~2k rpm, no load -

Engine idling, high beams on, hvac set to high, radio on -

Rev to 2k, all same loads on -

[Marvick08GT]

Me too! ^^^^ this, but also rear defrosters and seat heaters

 

Just came back from Rehoboth btw lol, rainy weekend

[apexi]

I trust that these guys know what they're talking about, like I said I don't know much about alternators and electrical. I would be surprised if it were the brushes, I disassembled my oem alternator with 217k and the brushes were still good according to the fsm. How many miles are on your legacy? Some pictures of my oem alternator below

http://legacygt.com/forums/showpost.php?p=5662453&postcount=1077

[Max Capacity]

OP, your in Boston...and you can't find a auto parts that will test the alternator...there has to be one around. Advance Auto Parts, Auto Zone, there has to be one of the major chain stores it's not like you live out in the stick's.

 

https://shop.advanceautoparts.com/o/storeservices?c3apidt=22650983713&gclid=CNbuu83RodUCFZCEswodLr0Leg&gclsrc=aw.ds

 

 

https://shop.advanceautoparts.com/web/StoreLocatorView?storeId=10151&catalogId=10051&langId=-1&filter=zip&json=true&rnum=10&min=1&max=10&latitude=42.3600825&longitude=-71.05888010000001&resolvedZipcode=02114&setStoreCookie=true&stPrefStore=&address=boston+ma

 

https://www.google.com/search?q=will+advance+auto+parts+test+an+alternator&oq=will+advance+auto+parts+test+an+alternator+&aqs=chrome..69i57j0l2.19918j0j7&sourceid=chrome&ie=UTF-8

 

http://people.csail.mit.edu/ilh/vacation/

[savethewagons]

Auto zone advertises all the time that they test alternators for free, and they are everywhere in our area.

 

 

Sent from my iPhone using Tapatalk

[jcaroth]

I'm planning to go to another Autozone or similar store soon, but I haven't had time. Work has been nuts the past few weeks...

 

In the meantime I'll try to log voltage when I get back to my car tonight, and I'll post some data afterwards. Thanks for the help everyone.

[jcaroth]

Alright, had some time last night to get some voltage datalogs. I warmed the car up as I drove home, then parked it and immediately took the following four readings for ~30 seconds:

 

- Idling, with no electrical load

- Idling, with high beams, hvac, radio, defrosters, etc all turned on high

- Holding at 2k RPM, no load

- 2k RPM with everything turned on high

 

I compiled the data in this graph. Seems to me that it's confirmed that either my alternator, voltage regulator, or cabling in the charging system is bad. I have some time to look into it after work tonight, so I'll keep ya'll posted.

[08SpecB_DE]

That looks normal. If the voltage dropped down to 12.8v under load I'd say your alternator is bad.

 

Wait until you start having the flickering dash lights and check voltage at that time.

[sunny5280]

Alright, had some time last night to get some voltage datalogs. I warmed the car up as I drove home, then parked it and immediately took the following four readings for ~30 seconds:

 

- Idling, with no electrical load

- Idling, with high beams, hvac, radio, defrosters, etc all turned on high

- Holding at 2k RPM, no load

- 2k RPM with everything turned on high

 

I compiled the data in this graph. Seems to me that it's confirmed that either my alternator, voltage regulator, or cabling in the charging system is bad. I have some time to look into it after work tonight, so I'll keep ya'll posted.

 

While all may appear good I would still recommend taking it to an auto parts store for testing. It's free.

[jcaroth]

That looks normal. If the voltage dropped down to 12.8v under load I'd say your alternator is bad.

 

Wait until you start having the flickering dash lights and check voltage at that time.

 

I've been getting the flickering battery lights for the last week or so after city driving for 20-30 mins.

 

Last night after work I stopped at two separate AutoZones to test the alt. They both told me it was fine. I drove the car home and checked the battery voltage with my multimeter. With the car off the battery terminals read 12.75V. At idle with no load, it hovered at 14.00V. At high load, it dropped to about 12.60V.

 

I checked the resistance of the alternator cable and got around 0.3 ohm. I quickly checked the fuse boxes but didn't see any blown fuses. I'm going to sit down with a multimeter and the service manual tonight and see if I can discover anything new.