Battery not charging
 

Well - my son and I have made some great progress on putting our project 88GT stang back together. I got him a set of underdrive MAC pullies for x-mas and other goodies. We were having battery charging problems before prior to installing a new battery, upgraded alternator to 130amp PA-Performance.

At best I'm seeing 12.4 volts across the battery at idle - turn on a couple of accessories and drops a little below 12 volts. Not good enough to charge the battery. Is there any know issues with inline fuse links with 88GTs that could cause battery not to charge right? Any ideas on areas to troubleshoot. Man these electrical problems sometimes are tough ones! Thanx in advance for any possible help.

Excuse me for asking, but how do you know for sure if that is not enough to charge the battery?

Normally you should be seeing around 14.4 volts across the battery while engine is running. If you're seeing right at 12-volts it's usually battery voltage and not alternator voltage.

Sounds to me like you said you had problem with an existing battery? If so:
Don't know about that particular vehicle, but same thing happened to me couple years ago. I checked everything, called a few shops, they told me to get a new battery among other things. I had a friend look at it, and he gave it back an hour later and laughed at me. It turns out the battery terminals were a little corroded or something, not even enough to see, so he cleaned them up and it was fine. This was after I spent to weeks trying to figure if I had a short or a bad alternator. I still feel stupid when I think about it. :)

Obviously if you have a new battery with that problem, just ignore the above, but it could be a minor connection problem.

Hope that helps.

Test the battery by itself. If it reads 12.6 or lower than it needs a charge. If you always have to charge it than something is drawing from it ( racing pulley doesn't help). The battery is problably shot too.

Does the starter growl on a start-up? If so it is shot too and it might be drawing too much from the battery.

You may have a fuse that is blown and is drawing from the battery too.

Good luck

Like stated check for corred post but it sound like the ALT isn't putting out enough. Has the ALT been checked yet??????? If not try that..

I have the MAC under drive pulleys and the 3G. I have absolutely no charging problems whatsoever. Even with all the accessories on when I rev the engine you can't see the head lights brighten up at all. This setup is a beast of a system. You must either have a bad battery, or a bad connection. Get a volt meter and start from the alternator and work your way back.

One question... when you installed the 3G did you upgrade the alternator wire that runs back to the solenoid? If not I'd recommend stepping up to 2 or 4 gauge welding cable. Check the ground from the battery to the engine block too.

You might try throwing another battery in the car for a day or so if you have one and see how that does. I took a battery to Auto Zone and they told me it was good so I searched for the problem elsewhere replacing everything along the way. I finally found myself right back where I started and bought a new battery which solved my problem =P

Good luck.

It's not the battery. It's either the alternator itself (unlikely), or too much resistance in the circuit back to the battery (more likely). The battery really is just there for starting the engine. After that, it's no longer used (while running) unless the alternator's output falls below 12.6vdc. Once the engine is started, the alternator replaces the the energy the battery spent starting the engine, which usually takes less than 30 seconds. After that, the electrical system runs off the alternator, not the battery, so a weak battery shouldn't affect the voltage reading across the posts while running. Connect a DMM at idle again, and observe it while accelerating to 2000 rpms. What happens to the DMM?

Take care,
-Chris

When I upgraded to the 3G alternator I did install the 4gauge charge wire for the increased amps. We have pretty much a brand new charging system with alt, battery and battery cables, even a new starter selenoid.

I'll test the suggestions you guys have and post the results - thanx again for the help!