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carss
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Feb 21, 2009, 11:45 PM
Post #1 of 13
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alternator problem
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Hello,,
grand prix, 3.1L, 1994, 130,000miles
car died and the alternator went bad, the mechanic told me to change the alternator. and i did and changed the battery too. two week later, the alternator reads about 8v, the mechanic did something and recharged the battery and the alternator reads 14v. one month later the alternator made the same problem and reads about 7-8v and the battery is totally dead. what to do? how i make sure that the alternator is bad or something else makes it bad?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Feb 22, 2009, 4:21 AM
Post #2 of 13
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Re: alternator problem
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Have the alternator bench tested. Parts stores like AutoZone and others will test them for you.
Charge the battery with a charger. The two work together and greatly enable each other. Neither is very happy about working too hard - alt can burn out trying, and batteries don't like being undercharged.
The voltage regulator and diode trio inside the alternator can go like a flash,
T
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carss
User
Feb 22, 2009, 7:30 PM
Post #3 of 13
(4520 views)
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Re: alternator problem
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No, my friend they said this alternator can't be opened.
But last time the mechanic charged the battery with a charger and every thing went good for couple of weeks, but why problem comes back.
thanks for your reply
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Loren Champlain Sr
Veteran
/ Moderator
Feb 22, 2009, 7:42 PM
Post #4 of 13
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Re: alternator problem
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Pardon my jumping in, here. It really sounds that you've got a defective alternator. It happens. As Tom suggested, you really should have it retested. There are different qualities of rebuilt units. Remember, you get what you pay for. We have switched to CarQuest reman. alternators and starters. They also have new ones available in increasing applications, but they can be considerably more money. And, it's not uncommon to get a whole lot number of bad units. Just because some el-cheapo parts stores have a lifetime warranty, that doesn't insure quality. Just that they'll replace it. GM alternators are about the easiest to open and replace the diode trio or regulator, but if it's still under warranty, you don't want to do that. Of course, make sure that all of your connections are clean and tight. And, that the battery is capable of accepting the charge. Again, as Tom mentioned, a defective battery can take out an alternator. And, discharging and re-charging the battery is really hard on it.
Loren
SW Washington
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Feb 23, 2009, 4:50 AM
Post #5 of 13
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Re: alternator problem
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>>Quote "No, my friend they said this alternator can't be opened." End Quote<<
They are opened all the time to replace common parts like this. Those parts can plain wear out or get destroyed from heat from overworking. The usual reason they say "alternator's can't be opened" is that voids warranties now as nobody knows how to do it. You used to have to "clock" an alternator so it was in the right position for a particular application.
Note: Rebuilts frequently only replace just the parts that will make it work again vs all new parts all over again. Many alts get sent back and just have new brushes, diodes or a bearing replaced and might check ok for a 2 second test, cleaned up to look new again and resold. Some have intermittent troubles and will test ok for a second but fail in real use too.
When you buy an alternator YOU aren't expected to open them up for anything and again - most places will void a warranty if you do,
T
(This post was edited by Tom Greenleaf on Feb 23, 2009, 4:51 AM)
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carss
User
Mar 10, 2009, 7:35 PM
Post #6 of 13
(4473 views)
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Re: alternator problem
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Hello again guys.
thanks you Loren and Tom
1. if i want to bench test the alternator at home, it's easy to see if brushes are worn out or not, diode can be tested, i believe, by multimeter it's one way open and the other way closed or have some resistance is that right?, but how i test the voltage regulator?
2. suppose the alternator and battery are both ok, what other problems could prevent the alternator form charging the battery? wires that i can see from battery and alternator look fine (the red wire, the only wire come out of the alternator is always hot, is that normal)
3. has the diode ever come out side the alternator in early 80's model cars? as my friend said he had same problem with his 1980 saab long age and found that diode is in line with the cable out side alternator.
thans alot you all,,,
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 10, 2009, 8:31 PM
Post #7 of 13
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Re: alternator problem
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Back to top you said this alternator was replaced just last month. Take it back as if you open it you'll void any warranty.
At home "bench" testing would be on the car as you would need to spin the thing. The parts stores have that machine and it either works when prompted or not - they (usually) won't be able to state just why just a go or no go.
I just searched around for simple ohms tests or what to ground for forcing it and nothing was good enough for me to post so I suggest taking it for testing.
All the parts are available but the trouble of late is the whole unit is available for about twice the price of each replaceable part one by one so not very cost effective.
Ok: Regulator and diodes are inside on any recent GMs that I've run across. If wiring looks perfect and YOU own this alt, you could open it and look for something burned. I don't know on this one what ohms should test what testing from what to what.
Yes - the red wire stays hot and should on this. The two wire connector should be for the gauge/warning light and with ign on will enable it to charge. There is a way to add ground or power to one of those to force output to max and I just don't know which so I'll suggest don't!
Perhaps Loren or another knows which you do what with on this - I don't and didn't just find anything credible to pass on for this Delco or possible Delphi alternator??
Again - less than a month - take it back,
T
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carss
User
Mar 10, 2009, 11:23 PM
Post #8 of 13
(4464 views)
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Re: alternator problem
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thanks a million tom for replaying so fast, as a matter of fact my alternator had only three days warranty as it is used.
you mentioned the two wire connector, i remember that the battery sign inside tha dash board does not come on. i did see it long time age but now i don't see it on. any clue
as i also said, if i charge the battery out side the car and return back, the alternator gives me 14v. which sounds it charging, then 2-3 days the battary dies and the alternator does not charge it if i jump start it.
thanks again tom, and i will tell if the problem is solved.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 10, 2009, 11:55 PM
Post #9 of 13
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Re: alternator problem
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3 Day warr! I'm shocked! Used is used but usually for the lower price they'll still give at least 30 day on anything.
Some things don't add up. Charge the battery (new or is it used too?) while it's in the car. Start it and read the voltage with the engine running - what is it then without a charger on it?
Does this have a volt gauge or just a batt warning light icon on dash or both. Generally when you turn key to "run" but not start the car the bulbs will light as a bulb check for which are working and go out when running. If there's only a battery warning light some much older GMs would fail to charge because of that but never heard of that since the 60s!
Note: If for any reason the battery is run down too low to start engine then just jumped the alternator would be overworked if it worked trying to charge battery back up and that alone can kill an alternator with high heat.
NoteII: While running you should see over 13v about all the time and if less there's a problem as well as over 15v a problem. You can put a volt meter if you wish hooked up thru power port/cig lighter if you don't have or trust a volt gauge on instruments.
You said it would last three days if charged off car! How many miles or how much run time is that? I'd like to see what the volts read with it running and then with it running with headlights on and fan blower on high with a raised idle. Report that and I'll have a clue on what next would be best.
One more - How much did this used alternator cost? Diodes are about $40 bucks alone and whole unit rebuilt ~$120 or so,
T
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carss
User
Mar 15, 2009, 8:04 PM
Post #10 of 13
(4442 views)
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Re: alternator problem
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Dear Tom
Battery is new... voltage on battery with charger on it 14v, charger away 9-10v
the warning light on dash stays on while engine is running even when charger on the battery
when battery charged off car to full it lasts about 30 miles with lights on and AC on
i checked the voltage between the wire connector while car is on on position and while it's running and voltage was zero and resistance was 36 ohms.
last, i bought that alternator for about $95 not from usa.
thanks all
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 16, 2009, 2:53 AM
Post #11 of 13
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Re: alternator problem
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Back:
If this new battery shows as low as 9v when charged! No need to report what the reading is when the carger is on it as you are just reading the charger - we need to know what the battery is by itself. A bad battery can easily kill an alternator.
Make sure you are charging posts to the battery and not just on it's cables as they might not be making a great connection. Take readings from the battery itself and not the clamps as well.
Side note: You can take a good brand new battery with no help from a vehicle's alternator to maintain it and it will run for a period of time till it's charge runs too low to run the vehicle. It isn't a cell phone battery - taking the typical lead acid car battery down destroys them in just a few total run downs.
Side note II: The common battery is made to be at 100% almost all the time. When you draw from it to start the vehicle it takes away some percent - like 5% of it total available charge if the vehicle starts right up - then the alternator will quickly restore the battery to 100% and the alternator is running the electrical items while running.
If you drop a battery to 50% with multiple failed starts or leaving something on by mistake the alternator will blow it's brains out trying to get it back to 100% and usually will. When you get down to 10-20% and they can get dropped to zero you are killing the battery and the alternator will constantly overwork, get so hot it ruins it.
The two need each other and either can kill the other so when you get caught with one bad make haste to be sure both are restored to good or it's just ping pong of repeated failures,
T
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hashhead
New User
Apr 14, 2009, 2:40 PM
Post #12 of 13
(4347 views)
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Re: alternator problem
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with motor off, battery showing 12.45 volts
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Loren Champlain Sr
Veteran
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Apr 14, 2009, 3:29 PM
Post #13 of 13
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Re: alternator problem
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hashhead; 12.45V is okay. A fully charged 12V battery will have 13.2V. But, at this point, all you are doing is showing surface voltage. If the battery holds a 200A load for 15 seconds and stays above 9.6V, the battery is okay. Once the engine is started, charging voltage should be between 13.6V and 14.6V. You'll need an amp guage to check for amperage output as well.
Loren
SW Washington
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