possible alternator issues

Pirate9687 · #1 07-26-2016, 03:53 PM

2004 4.0

Killed a battery on the highway, died while driving and when I got home it only was giving me roughly 1.4V. I threw my mega charger on it and even with surge charges it wasn't keeping a single bit of voltage so I assumed with it being that low, a mechanical failure in the battery happened.

New battery is in and I drove to and from work today with a battery light showing up just as I got home. Tested batV and it was giving me about 12V even..so..shit. I put my meter directly on the alternator terminal to bat- and I was getting 11.98VDC. Revved it up to roughly 1500RPM with no change and held it steady at 2000RPM with again 11.98VDC. Engine is running a little funny but I would not say its bad at all...more just like a little weak at idle.

My question here is - Is there a way to test the regulator (if it is a separate part on this model) to ensure it isn't failing instead of the alternator not putting out enough VDC? I would be rather pissed to replace my alternator to find it was a far less expensive part.

Additionally, am I potentially correct in my assumption that my mildly weak idle could be associated with batV barely hitting 12V, therefor not giving enough juice up for a strong ignition?

Thanks guys.

djfllmn · #2 07-26-2016, 03:55 PM

The voltage regulator is part of the alternator. And be forewarned if you want to only replace it once pony up and get a ford one

Pirate9687 · #3 07-26-2016, 04:00 PM

part of as in, built in and cannot be independently replaced?

djfllmn · #4 07-26-2016, 04:24 PM

Quote:

Originally Posted by Pirate9687

part of as in, built in and cannot be independently replaced?

exactly

mazdaman · #5 07-26-2016, 04:36 PM

getting approx 12v at the alt. is battery volts , you really need to test the alt. off the truck . bet you will find it is dead , i had one go , got it rebuilt worked perfectly , my truck now will show 14.4 volts right after start up then lowers to 13.6 once the battery is charged . at 12 v from the alt, the battery isnt getting charged

Pirate9687 · #6 07-26-2016, 05:34 PM

Exactly, anything less than 13 just isn't enough. I think I will be buying a new alternator then. Thanks guys.

JAMMANICA · #7 07-26-2016, 08:18 PM

Take the old one off, most auto parts stores have machines that will spin them and test them. Same with starters. Usually for free.

Mike In Bama · #8 07-27-2016, 01:29 AM

Here's a quick test to see if your alternator is ok.

An alternator produces three phase AC current which is fed to a rectifier system of (usually) 6 diodes. This turns the AC into DC with just a small amount of ripple in it. The battery acts kind of like a filter so that this ripple doesn't affect anything. If one or more of the diodes fail, that small ripple will become much bigger.

With the motor running, turn on everything you possibly can in the truck. AC, high beams, radio, emergency flashers, all of it.

Here is how to check your alternator with a good digital multimeter. Set the meter to the lowest AC Voltage range (Yes, AC). Put the black lead on the negative battery post and the red lead on the positive battery post. Run the engine at about 1500 RPM.

You should not read more 0.09 volts AC. If you do, you must rebuild or replace the alternator.

That's about as black and white as you can put it.