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I have a '99 Taurus. A few weeks ago I found that my car wouldn't start. The battery voltage was low. I gave it a full charge and checked the alternator voltage after starting it... 13.3 volts regardless of engine speed. The car runs fine, however if I don't charge it once a week, I'll end up with a dead car one morning.

Every car I've ever owned has always put out 14v or more when running, so 13.3v sounds like an alternator problem, however after a quick scan around the internet, it seems 13.4v is considered 'normal' or within limits. Is this correct? I don't want to drop a new alternator in and find out that's not the problem.

I'd appreciate any help, thanks!
 

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I have a '99 Taurus. A few weeks ago I found that my car wouldn't start. The battery voltage was low. I gave it a full charge and checked the alternator voltage after starting it... 13.3 volts regardless of engine speed. The car runs fine, however if I don't charge it once a week, I'll end up with a dead car one morning.

Every car I've ever owned has always put out 14v or more when running, so 13.3v sounds like an alternator problem, however after a quick scan around the internet, it seems 13.4v is considered 'normal' or within limits. Is this correct? I don't want to drop a new alternator in and find out that's not the problem.

I'd appreciate any help, thanks!
Likely the battery. 13.3 will keep it charged if the battery is OK. Not enough for a good alternator, but, bad battery is the first order of business.

With a new battery, and that voltage does not come up to at least 14.0 then likely the alternator. Very hard to replace and not cheap.

-chart-
 

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^^^^^ +1!
 

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^^^^^ +1!
Re to Jeff

Now thinking about it (dangerous) I remember, a shorted cell will make the battery ~10V instead of a ~12V battery. The alt will try to make it up to ~14 but cannot get it to that, so it will charge really hard. This could explain the ~13V limit. Bad for the alternator charging all out.

Important to get a new battery quickly and hope the alt is not damaged.
Although they are rated for 130A, they cannot stand to do that all the time.

Another type of bat failure is like my '03. Slow cranking. Put my "automatic shutoff" charger on it and it came up to ~14V and shutoff. Still weak cranking. This would be a near open cell. Ready to completely fail. New bat and it cranks BRISK. I like BRISK.:p

Bad battery will spoil a good alternator.

-chart-
 

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I have a '99 Taurus. A few weeks ago I found that my car wouldn't start. The battery voltage was low. I gave it a full charge and checked the alternator voltage after starting it... 13.3 volts regardless of engine speed. The car runs fine, however if I don't charge it once a week, I'll end up with a dead car one morning.

Every car I've ever owned has always put out 14v or more when running, so 13.3v sounds like an alternator problem, however after a quick scan around the internet, it seems 13.4v is considered 'normal' or within limits. Is this correct? I don't want to drop a new alternator in and find out that's not the problem.

I'd appreciate any help, thanks!
Edit: Welcome to TCCA.

Maybe consider running this puppy by your favorite autoparts store for a no cost in vehicle electrical system checkup, via their portable electrical system tester. Properly used, it should be able to sniff out the culprit.

Let us know what you find.
 

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13.3V is a BAD alternator. A good one will "pull" a dead battery up to 14.2V... If the battery is really "empty", the alternator will still try to raise the voltage to 14.2V. Because there is no curent limiter/protection, in most case the alternator will be damaged by trying to charge a completelly "empty" battery. There is a warning about that even in the installation leaflet.

Most likely your alternator has one bad diode. Drains back the battery and puts alternating curent in it too - probably by now that battery needs to be replaced also.
 

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13.3V is a BAD alternator. A good one will "pull" a dead battery up to 14.2V... If the battery is really "empty", the alternator will still try to raise the voltage to 14.2V. Because there is no curent limiter/protection, in most case the alternator will be damaged by trying to charge a completelly "empty" battery. There is a warning about that even in the installation leaflet.

Most likely your alternator has one bad diode. Drains back the battery and puts alternating curent in it too - probably by now that battery needs to be replaced also.
Really wish the little guy in my pic was readily available. Top notch diag tool. Anyone know where to get one might post. You ain't gettin mine.:lol2:

Agree with you but: battery is first order of business. If a cell is dead short, doubt alt can get it up to 14V, but I may be wrong.
No matter what, battery is likely toast if the alt is bad.
#1 battery, then test for volts.
If still not ~14+
Replace alt.

Just my take.

-chart-
 
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