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Discussion Starter · #1 ·
If I leave my key turned in the ignition for more than a few minutes it kills my battery. I don't own a multimeter so I'm using one from work, so I really need to know what the voltage is suppose to be when you check it from the battery terminals while the car is running.
 

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Normally 14.5 volts is what the regulator will try to produce. Under some circumstances the ECU will command the regulator to do 12.5v instead (but not until the engine is warmed up).

Seems like a bad battery or excessive electrical drain could be a possibility too.
 

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Discussion Starter · #4 ·
Ok well, then if its giving me a range from 8Vdc to O/L. Would that be the alternator? It stays on 13V for a few seconds and then random changes any where between those Voltages.s
 

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Dmitriy said:
Ok well, then if its giving me a range from 8Vdc to O/L. Would that be the alternator? It stays on 13V for a few seconds and then random changes any where between those Voltages.s
That sounds really wierd. Is this with the engine off or on?

If you have the interior light or headlights on do they vary in intensity?
 

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Discussion Starter · #6 ·
The engine is on, but no headlights or interior is on. It charges the batt. enough to start it again, but if I listen to the radio or leave the key turned for to long without it running it's to weak to turn the engine over.
 

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IIRC, even a fully discharged battery is supposed to put out over 8v. Turn the car off and check the battery voltage at the contacts. If you still get 8 volts, check that the electrolyte (aka battery acid) levels are where they're supposed to be.. carefully top up with distilled water if necessary. If the levels are fine, replace the battery.
 

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Dmitriy said:
The engine is on, but no headlights or interior is on. It charges the batt. enough to start it again, but if I listen to the radio or leave the key turned for to long without it running it's to weak to turn the engine over.
Sounds like your alternator or volt regulator is not working right ... you should see a steady voltage > 14v. It will have a fair bit of AC noise but it shouldn't be swinging so much that a DVM can't get a consistent reading. It could be the battery but I'm betting against that because a battery's that's screwed up enough to drag the alternator voltage down to 8v probably wouldn't be able to start the car at all. Some battery places will test your battery for free, so maybe you can eliminate that easily enough.

If the voltage is really going down to 8v while the car is running you should see a noticable pulsation in intensity when you look at any light that is on (headlight, dome light, taillight, instrument lights).
 

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Discussion Starter · #9 ·
'9445: Wow thats really odd. I just bought the battery. Shouldn't that mean its good? The strange part is the lights don't dim at all. I was just going to replace the alternator I have from my 89 si and see if that fixes it.
 

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Dmitriy said:
'9445: Wow thats really odd. I just bought the battery. Shouldn't that mean its good? The strange part is the lights don't dim at all. I was just going to replace the alternator I have from my 89 si and see if that fixes it.
Sorry, I wasn't speaking very clearly ... I was trying to say I thought the alternator or voltage regulator was the problem, not the battery.
 

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Inside the alternator, but it can be removed and replaced separately. On the other hand, it may be worth getting a fully rebuilt alternator due to normal wear on other items such as the commuter armature contacts.
 

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Dmitriy said:
Should I replace the Alternator with a spare I have and toss this one or have it rebuilt?
I would say yes, but I am suspicious of your voltmeter readings I guess. I would have expected that if the voltage was really going down to 8v while the car was running you would be seeing dimming lights.

Replacing the alternator's enough work that I'd want to exhaust the other possibilities first ... you might feel differently, and you've got another alternator already ... can't hurt I guess.

The other possibility I keep coming back to is that you have something drawing excessive amounts of power when the key is turned on. Really it shouldn't draw that much current if you just have the ignition turned on and nothing else on. You could try pulling fuses that are for stuff that is turned on by the ignition switch. If the meter you have access to has a 10A or 20A current setting you might try disconnecting one battery terminal, turning on the ignition but nothing else, and putting the meter in there to check the current draw.
 
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