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classic.car.fan

battery keeps dying while driving.

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on my 78 Lincoln mark V. car would not start, so i got a new battery. drove for about an hour. and then it died while i was driving and would not start back up. charged it then it started and died agan. I assumed it was the alternator. so i got it bench tested and they said it was fine. so what is preventing the alternator from charging the battery? voltage regulator? or something else?

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Voltage regulator would be something to check. Also be sure to check ALL connections to those items.

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Voltage regulator would be something to check. Also be sure to check ALL connections to those items.

If that checks out then make sure your belts have the proper tension. I assume the bench testing of the alternator was done using the pulley off the car, but it it's not properly attached that could limit your current generation as well. Finally check the continuity of the cables/wires involved.

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I've never heard of a car stop running because of a bad battery. I've even removed batteries from cars while they were running to swap batteries. None ever died unless they had a generator instead of an alternator. There must be something else going on in addition to the charging problem.

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If that checks out then make sure your belts have the proper tension. I assume the bench testing of the alternator was done using the pulley off the car, but it it's not properly attached that could limit your current generation as well. Finally check the continuity of the cables/wires involved.

i took the alternator out. and brought it to o'reilly auto for the bench test

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Could be the coil heating up and crapping out. Then it will cool off and run again.....for a few miles and crap out again. I speak from experience on this one.

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Could be the coil heating up and crapping out. Then it will cool off and run again.....for a few miles and crap out again. I speak from experience on this one.

I wonder how long it took you to figure it out. I had that problem on a car once. At one point I decided to have the pros figure it out for me and took it to the dealer. They did not figure it out either. Eventually, about 6 months on, after one of the bouts of poking at things under hood by the side of the road I noticed wax on my fingers. Started looking really closely at places and things that might have wax in them and spotted a crack on the tower of the coil.

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I wonder how long it took you to figure it out. I had that problem on a car once. At one point I decided to have the pros figure it out for me and took it to the dealer. They did not figure it out either. Eventually, about 6 months on, after one of the bouts of poking at things under hood by the side of the road I noticed wax on my fingers. Started looking really closely at places and things that might have wax in them and spotted a crack on the tower of the coil.

what coil are you referring to?

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Just about any battery place will check your charging system while you wait. I know that a lot of the auto parts stores do thia all the time. This way, you'll find out whats going on. The regulator regulates the amount of voltage being charged back to the battery, so if the regulator is bad, your battery might not be geting any charging voltage. Also like others have said, could be a problem with your wiring.

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Just about any battery place will check your charging system while you wait. I know that a lot of the auto parts stores do thia all the time. This way, you'll find out whats going on..

As Jim said, have them check the voltage at the battery before and after starting the engine, which will show you the charging system output, if any. Or, if you can not make it to the shop, borrow a friend's device and check it out yourself.

Forgot to mention, borrowing repair advice is the best reason to join an AACA Region or Chapter. (Promotional post:D)

Wayne

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To late for this little test now but a quick way to test an alternator if you have problems on the road is with a screw driver. In the center of the rear of the alternator there is a bearing or bushing, if the alternator is charging it creates a magnet in this bearing. With the motor running, stick the end of the screw driver up to the bearing, if it's charging it will suck the screw driver to it. If you don't feel anything it's not charging.

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You have my interest piqued Tommy. I'm running outside now to test your theory.;)

Who says you can't teach an old dog.......

Edited by West Peterson (see edit history)

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Is the light on the dash working? I once had a car that wouldn't charge and the "Alt" light on the dash was burned out. Replaced the bulb and that fixed the problem. Needs that small discharge to start the alternator field.

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58Mustang, Well, I don't know, but that car may have more than ONE coil........, example, COIL SPRINGS. hehehe

Trust it all works out,

Dale in Indy

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Check to make sure there is voltage at the battery end of the wire from the regulator.

Worn brushes can cause a lack of current so the alt. can not keep up with the total battery drain.

A Motor or Chilton manual will have in car tests you can do, (1978 had two different regulators)

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Take it to a good auto electric rebuilder. I stopped trying to fix my own alternators years ago. Also, I stopped buying parts store alternators because they are junk.

Last one I dealt with was a 2000 Ford Windstar. The battery kept going dead but the alt light never came on. I changed the computer, battery, belt, finally took it to the shop and they diagnosed a faulty rotor that worked ok at idle but put out barely any charge when revved up.

My local shop charges less to rebuild an alternator or starter than they cost at the local parts store, and the quality is far better.

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Like R.W. Burgess said, have you checked the battery voltage with the engine running using a volt meter (VOM or a DVOM)? If it is 12 volts or less car not charging. Check the voltage from the housing of the alternator to the positive alternator terminal as one check, and then check the voltage at the + & - of the battery. If you have about less than 13.5-14 volts you have a bad alternator, if you have that voltages it would indicate the car is charging so you have other problems.

As for the car turning off, that is very possible. If the battery voltage on most 12 volt cars drops below about 9.6 volts, the electronics of the car starts to shut off. Not quite as critical for cars prior to electronic ignition, but is true since.

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I've never heard of a car stop running because of a bad battery. I've even removed batteries from cars while they were running to swap batteries. None ever died unless they had a generator instead of an alternator. There must be something else going on in addition to the charging problem.

I am confused by this statement. It seems to me, that the electrical system doesn't care what produces the current as long as the current is there. Maybe at a low idle speed a generator will not put out enough power to run the engine.

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I had a bad ground cable once that did strange things and drove me nuts until I figured it out. I checked and cleaned the battery terminals a dozen times and it looked good. Turned out the cable corroded between the wire and the ground lug on the bolted end. Rare, but it can happen and you can't see the problem if the end is well covered.

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I am confused by this statement. It seems to me, that the electrical system doesn't care what produces the current as long as the current is there. Maybe at a low idle speed a generator will not put out enough power to run the engine.

Got your answer in your question.

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No, on some cars with generators, the battery is necessary to complete the electrical circuit. If the battery is removed, the circuit is opened and the engine will stop running.

A car at low idle will still run but the generator warning light will flash.

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