Voltage/charging problem

[WILOWNU]

95 tsi Fwd 5sp with 6bolt swap

The car will not hold a charge after its been jumped. While it is idling it will jump from 13.7 volts all the way down to 11.5volts and even 10.volts or below occasionally. I had the Alt checked not too long ago and everything was within spec. The battery doesnt look old at all either, so I am doubting it is the battery, but who knows. All the wires seem to check out cant find any bare spots or disconnected wires...yet. I was just wondering if any one had any other good things to check or if they have had this problem as well.
thanks!

 

[WILOWNU]

its funny that you should mention the belt.... I think my waterpump pully is on inside out, because the alt pulley and the crank pulley line up but the waterpump pulley is about 1/4" too far to the right.... not sure... however, the belt still spins the alt. I am going to go check the batter in about 10 and will post up... thanks!

 

[jongreene]

Get the battery tested.
Another little test for the alternator is:
1. get the car started
2. remove the ground cable from the battery
3. see if the car stays running.
If the car remains running your alternator is good.

Check your alternator belt too.

DO NOT do this , as the battery acts as a voltage stabilizer, w/o it there, the fluctuating voltage can wreak havoc on electrical.

Are you driving the car around after jumping? Make sure your driving it a good distance to FULLY charge the battery.

 

[Old Mitsu Tech]

Ok, once again. Like was mentioned above, your battery is a voltage stabilizer in addition to being a power supply for your starter. If you have voltage fluctuations, check for loose connections and make sure the battery is charged by a good regulated battery charger. I don't like using the alternator to do this as it's really just a maintainer. You can damage your alternator by deep cycling the battery and expecting the alternator to bring it back up. It will do this but at a cost eventually. If the connections are good and the battery proves good, then you likely have an alternator going bad.

 

[DGajre777]

+1 to what was said above.

NEVER ever charge any discharged battery with an alternator, it will end up killing it in a short time.

 

[1LE]

Well, glad to hear I'm not the only one... I've replace broken grounds, my battery, and my alternator and I sometimes see ridiculously low voltages while idling (especially if idling for more than several minutes). Have never seen as low as 11 volts, but it'll drop from the normal 13.7-13.9 all the way down to 12.1-12.3!

 

[WILOWNU]

I am taking the battery to the good folks down at autozone in the morning and having them check it. If it checks ok, I am going to have my Alternator checked... maybe its the voltage regulator inside, if so I will just do a full rebuild on the alt. I'll post up and let everyone know whats up with it. thanks guys!

 

[DGajre777]

Depending on the electrical load on the car, there is nothing wrong with the volts droping to 12.1 or 12.3 volts if you are driving around and come to a stop at a traffic light. But this low voltage should last maybe a second and the voltage regulator will bump up the volts back to up 13.8-13.9. An important factor to remember is that alternator output is directly affected by heat. A alternator on a car that hasn't been started will put out more output than a car that has been running for 2 hours. I vote for the voltage regulator being a problem. You can do a rebuild and just replace the voltage regulator or do a complete rebuild.

 

[WILOWNU]

its funny because right after I first jumped the car with the cables and let it idle the volts were around 15/14 and then slowly dropped all the way down to 10/9. Is there a test that I can do to find out if my voltage regulator is out of whack?

 

[RallyEclipse98]

What kind of battery is it? Take the battery and give it a slow charge. I'm talking at least 45 minutes. If the battery life is still sub-par then go from there. If you jump a battery, you should still charge it after if the jump was not held for at least 5 minutes.

 

[DGajre777]

its funny because right after I first jumped the car with the cables and let it idle the volts were around 15/14 and then slowly dropped all the way down to 10/9. Is there a test that I can do to find out if my voltage regulator is out of whack?

Yes, you can test the voltage regulator, but you have to take the alternator out of the car to test it. Any alternator rebuild shop can test the voltage regulator for you.

 

[WILOWNU]

Autozone said the battery was bad. Dead cell....they charged it for about an hour and then tested it. It is still under warranty, but from the previous owner. Anyone know a way I can get around that and get it for free? hah.

 

[1LE]

Depending on the electrical load on the car, there is nothing wrong with the volts droping to 12.1 or 12.3 volts if you are driving around and come to a stop at a traffic light. But this low voltage should last maybe a second and the voltage regulator will bump up the volts back to up 13.8-13.9. An important factor to remember is that alternator output is directly affected by heat. A alternator on a car that hasn't been started will put out more output than a car that has been running for 2 hours. I vote for the voltage regulator being a problem. You can do a rebuild and just replace the voltage regulator or do a complete rebuild.

Mine would sit at 12.1 for minutes on end while idling in grid. Heat does indeed seem to be part of the issue. Popping the hood would result in it climbing to 12.4-12.5...

I upgraded to a more powerful alternator since I have extra stuff on the car and frequently do long night rallyes in both very hot and very cold weather. Downside to that is the bigger alternator is well, bigger... Swapped my O2 sensor a couple weeks ago, and noted that I now have JUST barely enough room to do it (versus the tons of room I used to have)!