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Weird Electrical "Pulsing" - '93 Legacy Wagon

1993 legacy wagon electrical cold

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19 replies to this topic

#1 bopp

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Posted 14 November 2013 - 10:13 AM

I need some help with an odd electrical issue. (I could not find any existing threads on this, but please point me toward them if they exist!) This is a 1993 Legacy L Wagon with 226k.

 

About a year ago, during the cold Chicago winter, I started noticing the following behavior. At random times, the entire electrical system in the car experiences what seems to be a pulsating voltage change, like a sine wave, at around 80-120 Hz. All the lights pulsate bright-dim bright-dim in unison, and I can hear the cabin fan spin faster/slower in unsion with the lights. Sometimes, the Brake warning light on the instrument cluster will flash on and off in unison as well.

 

I know that the Brake light coming on is a failure mode for the alternator. The alternator is quite new and I had it and the rest of the charging system checked last year - it's all fine. I replaced the battery (needed it anyway) and also the plugs and wires (was having a starting problem). No change.

 

Over the summer, I did not notice this issue. This week, as the cold sets in again (30-50 F), I see the same issue.

 

The only suggestion I've heard is to check the grounds, but since the issue seems related to cold weather, I'm not sure that is the issue. I will have them checked at next service.

 

Any ideas on this? Thanks!



#2 ivans imports

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Posted 14 November 2013 - 10:15 AM

Sounds like a bad diode in alt change alt also check for corodedwires in bottom of under hood fuse box have been seeing problems there latly



#3 Cougar

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Posted 14 November 2013 - 11:49 AM

Make sure the fan belt isn't slipping. Like Ivans Imports basically already stated, this kind of trouble can only come from the alternator.



#4 Gloyale

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Posted 14 November 2013 - 12:47 PM

Turn the key to ON but don't start the engine.

 

Does the Check Engine Light come on and stay on?  or does it blink accompanied by a relay clicking?

 

The reason I ask Is that I've encountered a batch of bad "new" alternators out there.  

 

Since the ECU power and the ALT share a common cicuit on these cars  (90-94, changed in 95)  A problem in the alt can make the ECU do weird things hard starting......espescially when cold.....and other odd electrical behavior.

 

I've personally seen it twice and documented 2 other cases here on the board.



#5 ivans imports

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Posted 15 November 2013 - 11:11 AM

Have seen them hitt 16-20 volts anything over 15 ecu and curits start protecting themselfs but dont rule out under hood fuse box my 98 impreza had 4 broken wires on bottom of fuse box under hood



#6 porcupine73

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Posted 15 November 2013 - 06:58 PM

It does sound like maybe bad diode on one of the phases (alt is three phase). One test supposedly is if you put a voltmeter on AC and put it across the battery I think you're supposed to read less than 200mV. I had something go bad on my '00 and it was putting out 16 volts with some pulsing. The car did not like that at all. It sounded like it was misfiring, the ABS light came out, the check engine light came on. Then I shut it off and within a week it drained the battery too.



#7 coolskaterkid

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Posted 15 November 2013 - 07:19 PM

Turn the key to ON but don't start the engine.

 

Does the Check Engine Light come on and stay on?  or does it blink accompanied by a relay clicking?

 

The reason I ask Is that I've encountered a batch of bad "new" alternators out there.  

 

Since the ECU power and the ALT share a common cicuit on these cars  (90-94, changed in 95)  A problem in the alt can make the ECU do weird things hard starting......espescially when cold.....and other odd electrical behavior.

 

I've personally seen it twice and documented 2 other cases here on the board.

Interesting you mention this. I got a new rebuilt autozone alt last year, and first drive it did the same thing, overcharged pusled the lights, and i got the battery and brake light while this happpend, it also burnt out quite a few of my dash lights, along with boiling my battery. So i exchanged it for another one, no more pulsing but when i turn the key on, i get the check engine light blinks with a relay clickling, all along i thought my ecu was going to crap, it has the hard cold starting also that you describe, will go get a subi alt from junkyard and see if my issues go away. Thanks



#8 bopp

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Posted 16 November 2013 - 12:53 PM

Thanks everybody for your assistance!!

 

When I turn the key without starting, the check engine light turns on, does not blink, and there is no relay click. Quick visual inspection of the wires under the fuse box yields nothing, but I will check again more thoroughly.

 

Three follow-up questions:

 

1. Is it safe to let this problem go, potentially until the alternator fails more spectacularly, or am I risking damage to the electrical system, etc?

 

2. Does it make sense that the bad diode would only act up in cold weather? I did not see this problem today when it is 50 F outside, as opposed to 30-40F earlier this week.

 

3. Where do you recommend getting a replacement alternator? I'm seeing a lot of bad things about rebuilt alts from chain shops. Is an OEM unit from junkyard the best bet?

 

Thanks!!



#9 porcupine73

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Posted 16 November 2013 - 03:06 PM

1. I'd says depends on your risk tolerance. Myself I'd just take care of it now rather than know something is potentially on its way out and it is something that could leave you stranded and usually will fail at the worst possible time (assuming it is the alternator that has the issue).

 

2. Don't know but intermittent problems do occur.

 

3. Some people love the parts store alts; some people hate them. They do seem to have a lot of defects right out of the box. People say they like the lifetime warranty but I figure it's still your labor to R&R it each time, though granted on Subaru alternator replacement is pretty easy. You can get genuine reman but for that year it is probably like $300. You can use one for say a '96 Legacy, those are only like $70 genuine reman BUT the connector is a little different so you have to splice it in or get a harness piece from a '96 to replace the existing. I did this on a '94 Legacy and it's been working ok so far.



#10 heartless

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Posted 16 November 2013 - 08:06 PM

have gone thru a bunch of the "lifetime warranty" parts store alternators over the years - they usually only last a year or so before failing in one way or another.

 

I highly recommend finding a good shop that specializes in alternator and starter rebuilding and have a stock alt rebuilt by them. Might cost a little bit more than a parts store unit, but it is well worth it.



#11 eulogious

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Posted 26 November 2013 - 02:22 PM

Yes weather can and does affect how diodes work.  So yes, these symptoms would lead me to replace the alt before really doing anything else.  Weird stuff will happen once those diode(s) start to fail.  And keep in mind we are talking about a bank of diodes wired together, not just 1 simple diode.  So if one fails in the pack, then lots of random, weird stuff will happen, including your symptoms.

 

Buy the '97 reman unit from Subaru for about $90 out the door.  I had to call around to at least 2 different dealers to get it for $90 out the door, but if you got part numbers and know the price, they will eventually work with you.  My local dealer refused to give my the $75 price for it and wanted something like $180 for it, so I called another dealer 30 min away, and I ended up paying $89 out the door for the alt.  Why the local deal was being dumb, IDK.  I even called the local dealer back and told him I was going to go 30 min up north and get it for $90 and asked him to change his price to match because I wanted to support my local dealer, and he said no and basically hung up.  I know where I will NOT be getting any parts from in the future!

 

Wiring in the new alt is super easy.  Just cut the old plug off, and solder up the correct plug leaving the existing yellow wire disconnected.  Took me less than 10 min to wire it up.

 

Here's a link to my post on what I did to replace it and what I had to do to get it.  All the part numbers needed are included in the post...

 

http://www.ultimates...2-swap/?hl=1997



#12 bopp

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Posted 26 January 2014 - 10:59 PM

eulogius, thanks so much for your message and link! I've got the reman alt on order from my dealer for $85 out the door.

 

I have one major question. Does the reman alt come with a plug or wiring harness? If not, where can I get the correct plug end to splice into the existing wiring? Can I order that from the dealer as well? (Am I missing something here?)

 

Thanks!



#13 Cougar

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Posted 26 January 2014 - 11:22 PM

There is only a single plug on the back side of the alternator that should pull out with the wires connected to it. It's really a socket that fits onto the alternator. Be carefull with the main output wire as it is hot to the battery. If you short that to ground things won't be good and a fuse will blow. It is best to remove the battery ground lead before working on that connection. That way nothing bad can happen. After you replace the connections to the alternator then reconnect the battery lead.



#14 bopp

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Posted 26 January 2014 - 11:29 PM

Cougar, thanks for your reply! The issue here is that the plug on my '93 alt is different from the '97 reman plug (so I'm told), so I need the '97 plug in order to do the swap. I'm trying to figure out if the reman alt will come with the plug (unlikely), or if I need to order one from the dealer or find one at a pick 'n pull.



#15 Cougar

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Posted 27 January 2014 - 11:50 AM

Okay, I understand now. You are going to have to come up with one from somewhere. The sockets are not provided and the dealer will most likely want to sell you the wire harness as they don't sell individual connectors. You are most likely going to have to hit the salvage yard for that. 



#16 eulogious

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Posted 27 January 2014 - 12:35 PM

In the thread I linked to I posted the information about the plug you need.  And yes you need a new square plug.  You can get them off of a newer EJ series car or from certain years Nissan Maxima.  I went to my local yard and picked up the square plug off of an Impreza I believe and soldered it in.

 

One trick is that you don't really need the plug, you can just use female spade connectors to get the job done.  I would not do this and leave it has a permanent fix, but if you need to get up and running, the female spade connectors will get you down the road until you can get the square plug installed.

 

Good luck!



#17 bopp

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Posted 28 January 2014 - 07:42 PM

eulogious: Got it, thanks for that clarification! Do you happen to know what year Subaru switched to the rectangular plug? My local yard has a '96 Legacy - will that have the right plug, or is it still the round one? I can go check...when it isn't below 0 out here in Chicago...

 

Thanks so much for all your help!!



#18 eulogious

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Posted 28 January 2014 - 08:24 PM

'96 should work as its a 2nd gen leggy and I believe that they are the round plug. '95 and up should be square plug, but I am not 100% certain on that. But it should work...

#19 bopp

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Posted 29 January 2014 - 05:51 PM

The plug/wiring harness from the '96 is perfect - $5 and I was out the door. Got the reman alt today as well. I'll update after I do the swap! Thanks so much!!



#20 bopp

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Posted 04 February 2014 - 10:55 PM

Installed the new alt today - couldn't have been any easier. The new plug went on great with some crimpable connectors, and I'm going to put some split conduit on it tomorrow to clean it up. THANK YOU for all your assistance! What a fantastic money-saving modification! It'll be $90 total when I'm done.







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