Mystery Voltage Issue
 

Hello guys,
I've been having this issue for a while now with my 2012 Ford Mustang, and can't seem to narrow down on a fix. About 6 months ago my car died while driving, lost all power. After a quick tow we found the issue was some battery acid on the battery terminals which had been draining my battery until it gave up, or so we thought. After cleaning off everything and applying a protective spray, power was back. With it, though, came the new power issue. I kept getting low readings of ~10.8V which would sometimes go higher, but ultimately fall back down. Figured I blew a piece of the alternator so we changed it out but no dice. Both the old and the new alternator passed separate testing as well. After checking for power drainage on the mount for the alternator, various points on the engine block+grounds and the battery itself, nothing. Reluctantly tried bringing it into the dealership but was turned around by the mechanic saying he didn't wanna charge me just to say the alternator was bad, which I knew for sure it wasn't. I've ran down a majority of cables looking for a burnt section or rusted out connection points, but NOTHING has shown up. Even tested every single fuse trying to find a reason why this is happening. Losing my mind over this. Car still runs great, but I can tell the power fluctuations are taking a toll. My battery is somehow keeping a great charge and is stable at idle.
If anyone can think of another idea for a fix, please let me know. Last resort is taking it in to a mechanic who will cost me a fortune running down all these paths as well. thanks

Welcome to the forums! :wave:

That mechanic is correct, I'm thinking. It's your alternator. New doesn't mean working, it's why they have warranties after all. :yup:

That said... check your battery. Stick it on a charger sans any terminals overnight, really ensure it's charged up. Then take it off the charger and wait about an hour. Then go check it.

If it doesn't say 12.6 volts across those terminals, that battery is dead and is your problem. If not, it's a wiring issue, or more likely than not the alternator, or more to the point the voltage regulator in it.

I feel this is in order, sorry if you already know/understand this, but: There are two systems here. The starting system and the running system (aka charging system). The starting system is the battery. It's job is to run the starter and get the engine basically running. It just happens to be able to also run a radio, lights, battery backup, that sort of thing as a side job, but it's not the real reason it's there. It's there to start the car.

The running system is the alternator. And it happens to charge, sure, but that's not the primary purpose, that's it's side job. It's purpose is to run the car once the engine is started. It takes over the 12V duties, and the battery is briefly charged by the alternator's ability to run up to 14+Volts for a short time. After the battery's charged up (which normally would be a less than 10-15 second run) the alternator just puts out 12V for the duration of the run.

Yes, the battery can be used if the alternator is out of commission, but it will steadly drop from 12V down to 11, then 10 and so on until there's a point the car simply can't run anymore, probably about 7 or 8 volts, higher if lights/HVAC/etc are involved. That is a last resort option and you will kill the battery doing this.

So... given that info, and since the thing is hitting 10v and steadily doing so, that sounds like the regulator on the alternator is shot and you need another alternator.

It happens. Why? :dunno: Just does.

And of course, even though I'm pretty confident, that's a guess from *waaaaay* over here and you need a proper diagnosis. Any auto parts store should be able to free check the thing with their little boxes for ya. Those boxes are actually good at doing their jobs. If the boxes say "nope, all's good", then you either have a gauge issue or... well, I don't know what.

I dunno if that helps enough. But it's what I got. Good dang luck, let us know! :nice:

"And of course, even though I'm pretty confident, that's a guess from *waaaaay* over here and you need a proper diagnosis. Any auto parts store should be able to free check the thing with their little boxes for ya. Those boxes are actually good at doing their jobs. If the boxes say "nope, all's good", then you either have a gauge issue or... well, I don't know what."

Yeah this is about where we're at with it. Had the whole box thing check it while loaded and unloaded, and funny enough it acts better when everything IS loaded. Took the new alternator to two separate auto parts stores to have it tested and it checked out perfect from both. One suggestion I've received has been a bad ground cable from the engine block to the car's frame. I believe I haven't checked only one of them so it may be at fault.

With the Corrosion issue described in the first post I would also be checking to make sure the other end of the cable is not corroded as well as all the ground ends.

Help
 

Hello

the same thing is happening to my 2014 mustang car, changed the alternator and check the fuse box and the battery but nothing shows up and then suddenly overnight the battery drains in less then 24h, what was your solution to this issue maybe it can help me find a fix for my car.

- J

Consider submitting in the repair and service help sub forum section... You may also find a solution from previous thread submissions there as well... Thread link is also provided below, if interested?

https://themustangsource.com/forums/f804/

This Maybe Helpful!

https://themustangsource.com/forums/...ompany-549893/

KC