My battery terminals read 19.3 volts at idle, but my alternator (once removed) was fine on a bench test. Should I get a second opinion, or is there something between the alternator and the battery that is boosting the voltage? This is making my head unit ill, so I had to take it out. Any thoughts?

 

There are no other voltage sources in the car besides the battery and the alternator, unless you or previous owner added one. So nothing else could boost the voltage.

Voltage regulator (usually inside alternator case) should limit alternator output to about 14.5 volts. Sounds like yours needs further testing.

Just to check that you are reading the voltmeter correctly, what is battery voltage with engine off?

 

who did the bench test?
i'm prtetty sure the S uses an internal voltage regulator. go ahead and try a second opinon, see what happens.

 

It's gotta be your Alty. sounds like your regulator took a shiet. Careful cuz the battery will boil over and get acid ALL over the car!!

 

a local NAPA did the test, but he didn't offer any details other than a gruff "it's good." the battery reads around 17 volts with the engine off. i'll do a little more troubleshooting from the service manual tomorrow. i have to take an ohm reading from the ecu harness to the alternator harness, so i think i'll have to grow some longer arms.

 

and test another vehicle to make sure your voltage meter is working properly.

 

Our alternator has a control connection and is controlled by the ECU.

Not really sure what happens with an aftermarket ECU but I know the AEM doesn't control it.

 

Are you sure about how to use a voltmeter? I cannot believe your battery is reading 17 Volts with the engine shut down. It should read 12 Volts. If you do know how to set up and use a voltmeter, then try another voltmeter.

It's possible that a bad voltage regulator could allow the battery to recharge to this high of a voltage. But it would be a rare thing. Might not even be safe for the battery.

If you have an AutoZone or equivalent nearby, I would drive there and ask them to check out your electrical system. They have a small diagnostic cart that they roll out to your car. They attach a couple leads that look like jumper cables to the battery terminals, and ask you to stop the car, turn the key on, start it up, etc. The diagnostic cart will tell you what is wrong.

 

bleh. it turns out it was my voltmeter.....low battery. i put in a new one, and the car reads a happy 14.3 now. i suppose this a lesson to maintain your tools!