When my car is running the battery voltage sometimes drops below 12.5 volts. Is there any other reason that it may do this other than a bad alternator? I'm just wondering since I'm not totally sure how these alternators are controlled. It's intermittent (still trying to figure out exactly when the voltage drops vs load on the system), battery is new, and I don't think it's a connection issue. PCM is new. A new alternator arrives tomorrow but if there might be something else I'd like to test that before I commit to the alternator.

 

Well yeah only thing im thinking would be a bad ground or something like that. But if you say your battery is new i dont think it will be that. Try and get a multimeter and check the voltage should be above 12.6 and with the car on i think it goes to around 14.7.

 

At idle it goes between 11.8 and 13.2 depending on what accessories are on. I haven't done many experiments on it though. I figure alternator but I don't want to waste a new alternator when it could be something else. I can double-check the connections but I put most of them on with the engine out so I secured them pretty well. Doesn't hurt to check.

 

Yeah probably your best bet. But you have a point once the car is on the alternator should get all the load. The battery is only there to start the car

 

It's also having some weird issues starting. I'm hoping they magically go away with the alternator. If it is the alternator I'll be happy (I'll be happy when I find out the issue no matter what it is), but I'll be upset because I bench tested the thing at AutoZone before putting it in the car to avoid this sort of thing. I figured that they'd be more likely to give me a false negative than a false positive!

 

Lol well i wouldnt doubt they didnt know what they were doing when they bench tested that alternator

 

I would like to know what that tester does. It looks like it's missing an important test.

 

If i remember correctly from school its giving load to the alternator its has to reach certain specs to make sure it's working properly

 

bad internal voltage regulators can give problems similar to this, what sort of accessories are on when your seeing the drop below 13.2? I highly recommend you avoid parts store alternators and order a direct replacement bosch, denso, acdelco, alternator from rockauto.com should you go that route. I have had car's where we went through 3 or 4 alternators from the parts store before we would get one that actually worked properly. If your buying at an advance autoparts for instance, your going to be getting a "toughone" alternator. Which are absolutely horrendous.

 

Have to agree with spawne on that one

 

I had headlights, AC, radio.