I have a 2004 3.9 with 70,000 miles.

The battery started dying recently so I bought a new one.

The battery has continued to die though so that wasn't necessarily the problem.

From inside the car the needle in the battery gauge will drop way down and the little red battery light will come on, and I wont be able to start the car after I stop it, so its obviously not charging right, so I'm definitely suspecting that the alternator may be the culprit.

The only thing throwing me off is that this problem only happens about half the time.

Half the time there is no problem charging and the needle on the battery gauge is way over the halfway point.

I even got frustrated with it one day because the needle dropped all day and it wasn't charging so finally I headed to an Oreilly autoparts to get the alternator checked and on my way there the darn thing started charging just fine again! I still had the guy check it and ofcourse he said it was charging fine and there was no problem with it.

The next day though it stopped charging and I had to get a jump start again.

Has anything like this happened to anyone else?

Can an alternator go bad and still work half the time or is the alternator possibly NOT the problem?

Any help is much appreciated.
Thanks

 

That sounds more like a loose wire. Most alternators have a cable that bolts to the unit, and then a harness that plugs in. Check those connections before first!

 

yeah sound like a bad ground or what was said above

 

or what happened to me a few days ago, my idle pulley snapped off cause problems with the alternator and battery

 

Just sounds like a bad alternator. Mine did the exact same thing with roughly the same mileage. I just went to a guy and had him rebuild it for $100 and it was better than new.