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Discussion Starter #1
OK. here is the problem. The last three days I have taken Stang out for a spin after work and noticed that after I got back home, restarting was acting strange - like the battery was drained/weak. Today, I took SWMBO out for lunch and when we go to leave, Stang wont start! Battery acts weak. I get some help from some friends to give me a jump and I just get home ( 12 blocks later ) and Stang dies in the driveway. I am thinking my alternator is not charging the battery. If I can get it started after work, I am going to pull the + battery cable off and see if it stays running, if not - then the alternator must be bad? If it stays running - then the battery is shot? Problem is both are almost exactly one year old. Alt is a rebuild and the battery is a new Interstate battery. Things that make you go hmmmmm :p
 

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Please hear this... DO NOT pull the positive battery cable off the battery to "test" the alternator. You stand a VERY high risk of damaging the silicone diodes (also known as the voltage trio)! A MUCH smarter idea is to go to an auto parts store, and buy a cheap $10 voltmeter. I have a cheap-o voltmeter that tests battery voltage when the car is off, and when the car is on, it tests alternator output.

I have to turn people away all the time because they tell me they "tested the alternator" by pulling off the battery cable - I then tell them their warranty is void. Don't do it, it is foolish.

Anyway, I don't know what the climate is like in your neck of the woods, but a battery hydrolyzes very easily in hot weather - The mixture of sulfuric acid and water (known as electrolyte) needs to be perfectly in balance to achieve 12.6 volts - Try popping the top vents off the Interstate battery you have and checking the water level. The water should come to JUST the top of the plates - If it's below the plates, add only distilled water. Using tap water is asking for trouble.

Also check your battery cable connection to the alternator. A lot of times, a corroded cable will cause bad starter/alternator/battery symptoms and lead to improper diagnosis.

If the CABLES are OK, with no visible corrosion, I'd then check to see if the battery can HOLD a charge. A lot of times, the cell construction of a lead/acid/water battery an break down in heat, (as a function of hydrolysis) and cause a condition known as "a dead cell" in which one of the 6 "clusters" of power-giving chemical reagents simply does not work. This leaves less than 12.6 volts to power the car (as every cluster has 2.1 volts under optimal conditions) and thus, you have a problem.

Most auto parts houses including Checker (n your area) and AutoZone can test your battery on a load/amperage/voltage computer and analyze the cell structure.

Good luck!

Get back to us :)
 

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I just had the exact same problem, with all new parts that had been replaced in the past year or two. The battery was only 6 months old, alternator/regulator 2 years old, etc. A car running off the battery alone will act just as you have described. It will not start but if you jump it she can run for a while until it doesn't have enough juice to ignite the plugs.

I agree with NOT removing the + cable from the battery to test the system. I recommend the volt meter at the battery. At the battery you should see 13.5-14.5 volts with the engine running ~1500 rpm. If you read 12.0-12.5 volts, you probably have a problem with the regulator, wiring, or alternator. Check the battery water while you are there, but don't assume it is the problem until you can get more voltage with the engine running. If you search the forums, you will find a way to jumper the regulator to see if it is the problem. If not, clean all the contacts for the wires at alternator and harness plug and re-test. Clean all grounds too, at the battery, alternator, and regulator. Still not getting 13.5-14.5 volts at 1500 rpm? Remove the alternator and take it to a parts place with a tester. They can tell you if it is working or not.

By the way, my problem was a bad new(er) alternator. The cheapie rebuild unit I got from Trak Auto had a bad solder connection. I took it apart and resoldered it and it seems better than ever.
 

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Discussion Starter #4
Ok. I have a meter, I was going to test that first anyway. I plan to test the battery and all the cable connections for both corrosion and tightness. After that, I will restest the voltage at the battery. If it is weak. I will pull the alternator and take it to the parts store to have them test it on their machine. How is that for a plan? ::
 

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Like L20068 said, a volt meter can tell you a lot. The battery should read at least 12v on its own and around 14v at idle.

Put the battery on a charger overnight, it sounds like it needs it since it's been run down. Check all the wire connections in the charging circuit. Since Interstate is probably the best battery you can buy I'd suspect the alternator or the voltage regulator. Pull the alt and have the local parts store check it for you. If the alt is good and the battery holds a charge then I'd think the regualtor is the culprit. If the Alt is bad then I'd replace it and the reg, unless you replaced the reg along with everything else alt a year ago. Was the alt remanufactured or new?
 

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...and the regulator test. Here is that description of the regulator test that just reqires a 6" piece of wire and two female spade connectors:

Regulator test

Beware of multiple problems too. They are frustrating to diagnose because you are typically only looking for one problem. The regulator test only indicates it is not the ONLY problem, not that it is not A problem.

Good luck.
 
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