HELP! battery died!

[PorscheDV]

okay, i just purchased a 912E less than a week ago. P/O says he just replaced the battery. since then, each time i go to start the car the battery slowly but progressively has a harder time starting the car. now, tonight, the car wont turn over (i end up haveing to push start the car)

here's the thing, i havent been able to take a voltmeter to it, but i drive over an hour and a half and the car doesnt seem to be running off the battery (nothing gets dimmer) and the headlights brightness doesnt increase with RPM.

i heard about the alternator light being involved with the charging system. which light is that? (the red round one marked 'G')?? i'm planning on swapping out the alternator in the morning, but im open to ANY OTHER suggestions...

also, is there any other Alternator i can use for this car? (from another vehicle, that will fit?)

THANKS FOR ANY INFO...

[jabb]

If you push start or jump the car and it seems to recharge the battery I would think you have a short or some device that is staying on and draining the battery. If after an hour of driving you can key start the car that would imdicate the battery is charging. I would park the car over night with the battery disconnected and see if it starts in the AM. If it does it is not the battery. Also check the battery votage should be about 12.2. With the car running should be about 14 at about 2500 rpms.

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• Joe A.
• 84 911 Targa
• 75 914/6 3.0

[Joeaksa]

PDV,

Start from scratch.

Charge the battery with a trickle charger if you can, a fast charger is not real good for the battery and you want it topped up.

Put a digital VOM (volt ohm meter)(buy a cheap one at Radio Shack or the like) on the battery and check the voltage. Should be 11-12 volts. Start the car, should be 13.5-14.5 or so... a bit high is not a problem as long as its under 15, but not too much lower than 13.5. If the voltage is a bit low, take the motor up to 2000 RPM's or so and the voltage should come up.

If the value is lower than 13 or even equal to the reading you get before starting the motor, then your alternator/regulator is not recharging the battery.

If the value is above 13.5 then start turning things on... like the lights, fan, back window heat and see if the alternator will pull the load. If it keeps the voltage up then you are doing fine, if it drops below 13 or so then its not pulling the load and either the alternator or regulator needs replacing.

Drive the car for a while then do the same checks to see if something is breaking down after it gets warm. Not too unusual for the alternator/regulator to drop offline when it warms up.

If all the above checks out then get the battery checked out. Could also be a short (light left on, or such) that is draining your battery. To check this, charge the battery and then drive the car. Where ever you stop take the negative battery cable off. When you return put it on and continue like this for a few days. If the car/battery works fine like this then you have something in the system drawing it down at rest... not good and a ***** to troubleshoot at times...

If the alternator/regulator is tits up, call around and find a local shop that would rebuild them. Do not go to Porsche as they charge you an arm and leg for the thing. Takes less than an hour to pull it out and same to put it back in, look on Pelican for help on this.

Hope this helps...

JoeA

[Formerly Steve Wilkinson]

I just faced--and with the help of John Walker's advice--solved the exact same problem. All of the advice above is good in terms of finding out if your alternator and battery are good. If the battery is good and the alternator is charging, here's the next thing you do. (Worked for me.)

Take the positive lead off the batter post and put a voltmeter/multimeter between the post and the positive lead, with the ignition off. If you see a draw of about 10 volts, it's stuff like the electric clock, radio memory, security system etc, and that's normal. If, however, you see a draw of 11.8 or 12 volts (depending on how fully charged your battery is), you have a dead short somewhere, and that's where your power is leaking out. One by one, remove every fuse and relay in the trunk and engine compartment and watch the voltmeter. If one of them causes the reading to fall to 10 volts (the permanant-draw stuff) or virtually zero, if you've already disconnected stuff like the electric clock, there's the short--in whatever wire(s) is connected to that fuse.

The final thing you do, if none of the fuses or relays pulled solves the problem, is crawl under the car and disconnect the fairly hefty positive lead to the alternator from the starter relay. If that fixes the problem, you've got a bad alternator diode or something of the sort.

Stephan

[PorscheDV]

ok, sorry guys, thanks for all the great advise, let me clearify i few things...

i dont think its a bad battery, i dont think its getting a charge...i push started the car and after and hour and a half of driving it still wouldnt turn over. the P/O says its new, (ill have it checked out) i believe its the alternator, but have yet to test it with a voltmeter (need to get one!) i jumped it today (i had a quick thought it might be a bad starter...but turned over/started fine)

so, im off to have the battery checked...if thats ok...i'll check the alternator...im worried its a short or something a step further than just the alternator...

one thing to note though...before this all happened (since ive had the car) when the engine is runnning i can turn the headlights on...if the engine isnt running (with or without the ignition turned to the on position) the headlights wont come on, but my orange indicators will...related?

TIA

[PorscheDV]

Hmm...is it me...or is my reply after stephans post not showing up?!

[davis911s]

Your computer isn't refreshing your pages automatically, hit the refresh button on your tool bar.

Shawn

[john70t]

A short-cut
for finding shorts:
Pull the negative cable off the battery and put a DVOM set to amps in between them. 2-3 is ideal(i think) for radio/alarm, below 1 without. Some may be higher.
Pull fuses one at a time untill draw is zero. That circuit is where to start. Disconnecting"branches" will isolate furthur.

[Formerly Steve Wilkinson]

If you don't have a multimeter and you're trying to find an electrical problem, you might just as well be rubbing two sticks together. You can have a perfectly "good" alternator, in that it charges just fine, and it will still drain your battery flat if a diode is bad. About all you know at this point is that your battery accepts a charge and your alternator provides one. But your problem is that you have a short. That is what causes batteries to drain when the ignition is off.

Stephan

[Joeaksa]

Go to Radio Shack or another electronics store and get a digital VOM. As Stephan said, until you do this, you might as well be rubbing two sticks together until you do this. You can usually find a cheap one for under $20 and its well worth every penny.

JoeA

[Early_S_Man]

There are disadvantages to the cheap multimeters under $30 in that they have more displayed digits than their accuracy justifes, which leads to false security. Read the specifications of any digital multimeter you contemplate buying! Stated accuracy on the DC Voltage scale of 2-3% is not really any better than most analog meters! It really should be 1% or better for good confidence.

It would be better to go to Sears and get a meter of a known good brand such as Fluke, even if you have to spend $60-$80.

Some meters in the $75 to $130 class have serial ports and included data logging software that can be run on a laptop computer and can be very helpful to use in-car while troubleshooting during a test drive. Usually, such software has variable sampling intervals ... such as once per second, or once per minute. Later, after the test drive is over the recorded data can be displayed on a graph, printed and analyzed.

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler