MythEyeLess

Hey guys, I'm having a difficult time with this car. It's a 2006 3V Saleen mustang, and it keeps draining my battery. I thought it was the battery at first, so i had it replaced, it will last for around a month before it dies as well. Next up i took it to a shop, they told me it was the alternator not having enough power to maintain the power under load. Changed the alternator, got a bad one, replaced it with a new one, same problem. Now it only lasts 2 days before the battery dies, this is just quick recharge by the way, not a brand new battery. The voltage gauge seems to indicate that the alternator is doing it's job, except when i turn on the air conditioner, lights, and radio, i see it slowly go down to half before it picks back up. I haven't competently checked for a parasitic drain, however if i leave the car sitting for a week, the car will start just fine, it's only when i run it that it drains. I'm out of ideas of what it can be, any help?

Nuke

Buy a PA Performance alternator and replace the battery unless the current one load tests good. Also, be sure your headunit is off when you turn off the ignition. The amps in the Shaker systems are known to remain on in the '06s.

With a sick alternator, when you drive the car, the alternator isn't keeping up with the demand and it's draining the battery. When it sits the battery still has whatever charge there was when you shut it off plus a bit of recovery.

tx_zstang

I replaced a battery with a new one, and it would randomly fail to hold a charge for various periods of time. Replaced it under the battery's warranty and have had no issues since.
And +1 on making sure the radio is turned off before turning off the key.

bryan67

well use a meter check you alt. output with all loads on. you should have 13.4 volts or better. If you added any extra loads you may either have to replace the ALT. or Upgrade to a higher amp'd one.

MythEyeLess

It was a PA performance alternator. The car doesn't drain unless the car is started though, which is what really gets me. If i leave the car with the battery attached it will hold charge.

I also had a problem where when I was reaching a stop light the engine would almost want to like stall, before it picked back up again at normal idle. It's a weird thing. I've already replaced the alternator, and the battery multiple times, enough to think that's not it. I don't know if they have anything to do with each other.

MythEyeLess

under load it dropped to 12.8. Which PA said it was still high enough for their alternator to be considered "good".

MythEyeLess

I've already replaced it 3 times. Holds for about a month and then it just dies.

Nuke

I suspect the reason that the battery is ok when you don't drive it is because there's nothing but the normal parasitic drain on the battery. When you run the car, the alternator is obviously not keeping up with the demand which requires the battery to pick up the load which in turn drains the battery. At every startup, the battery is weaker than the previous startup.

As odd as it may seem, you must be getting defective alternators. And 12.8 volts under load AND with the battery weak is NOT acceptable from an alternator. If you're not seeing 13.4 -13.6 volts, the alternator is NOT ok.

bryan67

if your only seeing 12.8 then IMO you got a problem should be over 13.4. Do you have underdrive pulleys?? 12.8 is that at idle? does it go up off idle?

roegs

There have been many good suggestions on this. I'd agree with the others about 12.8 being low for the alternator. I'd also check for other items that could be drawing a heavy load while the car is running. Those include constant radiator fan operation (possibly from a tune), aftermarket audio amps, additional or aftermarket headlights and/or fog lights, and a faulty rear window defogger (relay stuck in on position). Also, the thought about under drive pulley's is worth looking at.