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My Wagon blew 2 Alt's... Why???


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17 replies to this topic

#1 TheSubaruJunkie

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Posted 17 September 2003 - 02:06 AM

My '84 GL Wagon's alternator had a bad voltage regulator, so i put the alternator from my brat into the wagon. Today after driving the car for 2 hours and parking it, i went to start it and it started right up but...

the voltmeter jumped to about 14 volts, then dropped to below 10volts. all the dash lights came on and i tested it and the car dies when the Negative is pulled.

What would cause this? I wired my Stereo, CB and Amp the other day. Wondering if maybe my wiring is bad?? All 3 items are running off the same lead comming straight from the battery. Then they are grounded to the chassi.

I pulled the lead from the battery after it blew. Wondering if I should re-wire it all.

-Brian

#2 GLCraig

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Posted 17 September 2003 - 02:45 AM

Well for starters any car will die if you pull the negitive from the battery.

What it sounds like is you have one of the following: a bad ground somewhere, a short, or a ground loop.

#3 TheSubaruJunkie

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Posted 17 September 2003 - 02:53 AM

I was under the assumption that if you pull the negative from a running car, it will remain running if the Alternator is putting out power.

Can you explain a ground loop to me pls.

im electronicly stupid unless it's a computer.

-Brian

#4 Cougar

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Posted 17 September 2003 - 10:11 AM

In answer to your question about a ground loop, it is having multiple ground points in a line that has voltages in between the seperate ground points. Having a single ground point keeps this kind of thing from happening. Unless your main battery ground lead is not connected properly I doubt you have a problem there.

It may have been just some bad luck that caused the second alternator to go out on you. I would get a rebuilt one to replace back in the car and check out the battery and wiring before you put it back in the car. The alternator's main output lead to the battery should not have any resistance in it. The battery should be checked out, load tested and fully charged before putting in the new alternator. If the battery is more than four years old I would think about just buying a new battery as it will not last much longer and you will have more trouble down the road.

After you have everything in and running I would have the current flow checked to the battery to see if something is drawing excessive current and damaging the alternator.

#5 subieman

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Posted 17 September 2003 - 10:15 AM

Brian, The voltage regulator went out on my 84 hatch a while back so I replaced the alternator with one from Kragen. 1 month later it went out again! Grrrrr I got a free replacement but I hope it's not something shorted in the car thats doing this. Let me know what you find out.

#6 MorganM

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Posted 17 September 2003 - 11:08 AM

Originally posted by TheSubaruJunkie
I was under the assumption that if you pull the negative from a running car, it will remain running if the Alternator is putting out power.

Can you explain a ground loop to me pls.

im electronicly stupid unless it's a computer.

-Brian



This is how I always check them and it does work. Any car that had a good Alt. would keep on ideling when the battery was dissconected. Prolly not the best/smartest way but it beats pulling the Alt, dragging it to a shop and having it tested only to find out its OK

#7 calebz

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Posted 17 September 2003 - 11:17 AM

True, pulling the battery cable will work on most cars that are not heavily computerized(my saab 9000 for example was built to shut off if the curcuit was interupted by the pulling of a cable) .. however, it is a good way to fry an alt... especially a tempermental sooby alt.

#8 NV Zeno

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Posted 17 September 2003 - 11:50 AM

Just throwing this out there, but wouldn't fuses be blowing if there was a major short somewhere?

If both your alts are Kragen aftermarket, chances are they're toast. Here's a golden op to get 2 alts for the price of 1: Buy a lifetime warrantied unit from Kragens (bring your core), and return the second one as defective. 2 lifetime alts for 100 bucks or so..helluva deal.

#9 archemitis

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Posted 17 September 2003 - 04:19 PM

i thought you could only pull the positive... suppose it doesnt matter though

#10 VaporTrail

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Posted 17 September 2003 - 04:31 PM

right, you'd have to pull the positive cable, then all the juice would come from the alt (which is what normally happens when it's running/charging properly....

question: when it's running, do you see a noticeable momentary drop in the voltage when your turn signal flashes? not the hazard cuircuit, but the actual turn signals.

if you have power windows, does it drop also when raising or lowering them?

these are the sysmptoms I had when I lost 3 alts in about 4 months. ended up being the accessories circuit from the ignition switch. all my connectors were good, but there was a problem in the wiring somewhere. to reduce the load on that circuit, I cut the wire going to the fuseblock section for the ACC circuit. I used a relay switched by the existing ACC circuit (which normally fed the panel), then had a direct 12V line from the battery feed the Relay, then into the normal ACC circuit. this way the load was all on the direct feed instead of the ACC feed from the ignition.

have never had another problem since, and no more jumping voltmeter....

#11 TheSubaruJunkie

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Posted 17 September 2003 - 04:50 PM

When the alt was in my brat, i did notice it would move when the blinkers were on. And if the AC Fans were on or not.

I redid most of the main wiring for the positive and the negative, replaced the alt (with another used one I had) and replacing the battery with another one.

I need to go over the wiring for my stereo and make sure its grounded correctly. Then take the car for a test drive.

I have aprox. 28 hours until I leave for a road trip to Oregon. Dont watn my car dying on the way.

-Brian

#12 Flowmastered87GL

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Posted 17 September 2003 - 04:56 PM

Hmmmm my voltmeter jumps on my 87 GL when I hit the turn signal.... Maybe thats why I have eaten 3 alternators in the past year :(

Gotta love lifetime free replacement :headbang:

I just had the battery fluids topped off too, it seems to be a little more consistent voltage now.

#13 GLCraig

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Posted 17 September 2003 - 05:09 PM

deleted

#14 bushbasher

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Posted 17 September 2003 - 11:26 PM

a car runs when you take the battery leads off, the alternator powers everything anyways. The battery is only used to start the car and to power anythin when the engine is off. If the alternator is working properly the car draws no current from the battery when running, so I don't see how pulling the leads off will hurt a good alt.

#15 Cougar

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Posted 18 September 2003 - 03:08 AM

The alternator's output can be noisey and the battery acts as a filter for the noise. The battery also smooths out the pulsing DC output of the alternator. To me, it is not a good idea to remove a battery lead while the engine is running. You may get away with it but you are asking for trouble by doing it with the ECU and other electronic circuits. The easiest way to check the alternator is to have a load of some sort on the system, like the headlights on, and then measure the voltage of the battery while the engine is running around 2,000 rpm. The voltage should stay up around 14 volts if things are ok. If voltage goes below 12.25 volts, there is a charging problem and some troubleshooting should be done.

#16 TheSubaruJunkie

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Posted 18 September 2003 - 04:11 AM

My volt meter will hold steady at 12 with the lights on and the A/C fans on. With everything off, it will get up to 14 and stay there. At idle, 900rpm-1200rpm, it will be around 10 or 11.

No more time for troubleshooting. Im going on a 800 mile round trip to Oregon and back in less than 2 days. I have to do an oil change, change the gear oil in the tranny, pack, shop, then drive 5 hours for a camping trip.

Lets just hope this alternator doesnt freak out, and the battery stays good.

-Brian

#17 Cougar

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Posted 18 September 2003 - 12:20 PM

It sounds like your alternator is a little weak Brian but, you should be able to make the trip with no trouble if things stay the same. You may have some diodes out in the rectifier circuitry of the alternator. I would have a load test done on the alternator at a shop when you get the time to check things out further. They can check the battery out also while you are there.

Have a good, safe trip and enjoy the nice country there. Oregon is definately good "Subaru Country".

#18 TheSubaruJunkie

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Posted 18 September 2003 - 02:00 PM

Oh, i know. This isnt my 1st trip up there :) Oregon is great, cant wait... hope my car doesnt leave me stranded.

-Brian




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