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is alternator bad?

4K views 25 replies 7 participants last post by  71 Chevy 
#1 ·
I bought a brand new reman 94 amp alternator from autozone. I had them test it in the store and they said it was good.

well, here is my problem. with the car idling at 1000rpm, voltage at the alternator post is only 12.28 volts.

could anything else be wrong other than the alternator? its a 12si internally regulated
 
#4 ·
It's not working correctly. Each cell of the battery will make around 2.2 volts X 6 cells. The battery should be at or near 13.2 volts the best I remember. If the alternator doesn't produce a minimum voltage greater than the battery has in it it will not charge the battery.
 
#8 ·
its a basic 12si alternator. I dont think it requires 12 volt input but I might be wrong. my undertanding was that it is self grounded, the main post goes to the charging stud, one small wire also goes to the charging stud to sense the voltage, and a final wire goes to the dash warning light. I have everything hooked up except that wire that goes to the dash.

I have three meters. a voltmeter gauge, a multimeter, and the built in gauge in megasquirt. they show almost the same thing
 
#18 · (Edited)
I think it is working now, because the ignition seems to be firing better(engine also running a lot leaner), and the car wont switch off when I turn off the ignition.

wtf?

someone tell me if this is wired incorrectly:

the ignition is wired to the battery through a relay that is activated by the ACC connection on the fuse box.

it should stop firing when I turn the key off right? well, the car wouldnt stop until I pulled the lead going to the distributor off the relay. whoa, scary.

any ideas? I would have thought maybe it was dieseling from being too lean, but it died instantly when I disconnected the hei, making me think the relay was somehow not switching off with the key switch when the alternator is energized.


IDEAS??? PLEASE



edit: ok, i found this
http://www.jeepforum.com/forum/showthread.php?t=571743

has anyone installed a 10si or 12si and had this problem? something about back feeding the ignition
 
#21 ·
well it looks like the sense wire and diode did the trick

the sense wire to energize the alternator and get it started,
the diode to allow the engine to stop when I turn off the key.

gauge was bouncing between 12.5 and 14.2 at a very low rpm, between 400-700 rpms, and megasquirt says I was at 13.1 volts for the 10 seconds it ran. I call this a pass.

thanks all
 
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