battery or alternator: Please help

[mptoledo]

I have searched and read all the results on the subject. I just need a little more input.

Went to start my car after the winter sit. Got a new battery as my 7 year old one wouldn't start the car. It is 50ish outdoors. I installed the brand new batter from wallyworld. It is their best gold series. Had some trouble starting it and got an arc when connecting the cables.


2001 boxster "s" 62k miles. Ran perfect before winter.
1.) Battery light stays on
2.) stereo won't turn on(aftermarket jvc).
3.) oil check thing doesn't work, it just blinks
4.) Car stops the second you take off the negative terminal.
5.) Checked all fuses and replaced abs/asr/psm control unit as it had blown

I ran the car around the block for a couple miles gently but spirited once it warmed up. Every thing seemed as usual and no other issues, except the above.

I think I blew my alternator out but is there another way to check or does someone else have an idea?

[JFP in PA]

Originally Posted by mptoledo

I have searched and read all the results on the subject. I just need a little more input.

Went to start my car after the winter sit. Got a new battery as my 7 year old one wouldn't start the car. It is 50ish outdoors. I installed the brand new batter from wallyworld. It is their best gold series. Had some trouble starting it and got an arc when connecting the cables.


2001 boxster "s" 62k miles. Ran perfect before winter.
1.) Battery light stays on
2.) stereo won't turn on(aftermarket jvc).
3.) oil check thing doesn't work, it just blinks
4.) Car stops the second you take off the negative terminal.
5.) Checked all fuses and replaced abs/asr/psm control unit as it had blown

I ran the car around the block for a couple miles gently but spirited once it warmed up. Every thing seemed as usual and no other issues, except the above.

I think I blew my alternator out but is there another way to check or does someone else have an idea?

Get a multi meter, check the battery voltage with the car off; should be 12.5 V or so. Start the car, check it again; should be ~14.5V. If it passes both these test, your battery and alternator are fine, you have shorted out something else. If it fails either test (low car off voltage can be a battery issue, less than ~14.5V running and your alternator is bad), you need to fix these issues before determining what else is wrong..............

[Steve Tinker]

As an addition to JFP's advice, if you disconnected the battery with the engine running as per your item#

4.) Car stops the second you take off the negative terminal.

there's a good chance that you have blown the diodes in the alternator......

[mptoledo]

Funny you should mention that. I read that in one of my searches after I had already done it. Live and learn. I guess 9 years on an alternator, I got my moneys worth.

Why would my oil check guage not work? that is what I can't figure out. It just blinks and doesn't do anything else

[ARModen]

The battery light is really an alternator light, which generally indicates that there is something wrong with the alternator or the voltage rectifier/regulator on the output. The ones I've taken apart sense voltage at the diodes, so the light coming on indicates the alternator is no longer rotating, or the diodes have burnt out. So it could be a pulley issue, but you get a lot more lights if you throw the belt.

Most of the electronics in the car will run down to 5-8VDC. Below 8VDC you start losing sufficient potential to generate an arc at the plugs and run some larger loads effectively. If you're alternator isn't working then you have 12.5VDC from post to post on a fully charged battery. Battery voltage drops as load increases and the battery discharges so 10-11VDC is reasonable while driving. Any sort of grounds or dirty connections or large loads (headlights) can drop portions of the electrical system another 2-4VDC. This is fine if you're starting at 14.5VDC but enough if you're at 11VDC, which is probably what you're seeing. 5VDC is probably enough to still run the instrument cluster, but not enough to run the oil level sensor. My old 944 had dirty battery terminals that were dropping ~6VDC. They were hot from dropping that much power.

Bottom line, fixing or replacing the alternator and then driving the car around a bit will probably fix your problem.

[mptoledo]

No new noises or anything pully related. I pay close attention to sounds in my car after the "ims" scare of 2009 on here. I think when I arcd my battery installing it, I zapped the alternator. I new I did a bad thing when I saw a fews blown and my rear spoiler had gone to the up position.

I am just thinking of taking the alt in tomorrow, but I will decide that after I attempt to take it off. What I have read it isn't that muchof a big deal. Cant' be as hard as when I replace my alt on my girlfriends Taurus. Some genius really screwed the pooch when they desinged that engine.

[vipola]

Originally Posted by mptoledo

4.) Car stops the second you take off the negative terminal.

I would NOT do that, even if it was a good test a while ago, with today's fancy electronic, you don't want to unplug the battery on a modern car/motorcycle while it run. The battery help to keep the voltage stable and prevent it to spike.. it's not intent to run without a battery.

Originally Posted by ARModen

The battery light is really an alternator light, which generally indicates that there is something wrong with the alternator or the voltage rectifier/regulator on the output.

I learned this one the hard way, been a motorcycle guy for ever, when I saw the battery warning light up I tought it was a low voltage indicator and I went for a ride to 'recharge' the battery.. and got stuck when the battery died in the middle of nowhere 15 min later LOL..

[mptoledo]

Thanks for the reply. Since I just got the battery today, I am pretty much ruling that out. I am just going to take the alternator to Oreily's tomorrow. It is the original and I am pretty sure I fried it.