Alternator for 3rd Generation V6

[fizzer]

Hello, my alternator recently failed so I purchased and installed a replacement. However, the bearings in my replacement don't seem nearly as good as my old Motorcraft as the replacement will not freely spin nearly as long. I figured I may as well see if I can repair my original Motorcraft so I purchased a new set of brushes for it. I installed the new brushes and then swapped alternators again.

After installing the old alternator with the new brushes I received a "Check Charging System" error with code P0620. The strange thing is that I am getting 14.2V at the battery. I put the replacement alternator back in and the error goes away. I am not sure why I am getting a charging system error when the output voltage seems fine but I figured the next thing to try replacing is my voltage regulator. The problem is, I cannot figure out which one to buy. I have found regulators for Ford 3G Alternators but I am not sure if my 2005 Mercury Mountaineer is a 3G or a 6G? Also, it seems that there are a couple of different sizes of the 3G.

Does anybody know if the 3rd Gen 4.0L V6 uses a 3G Alternator? When ordering a voltage regulator will it matter on the type/size or can I just order any voltage regulator that will fit?

thank you.

 

[fordbluefamily]

In 04 Ford switched to a different alternator that has the pcm wire on it. That code is for generwtor control circuit and related to that pcm function. I am told you need internals specific to the 04-08 alternators if that helps any. Also, it is not uncommon for a new bearing to spin "stiffer" than a worn out one. Give it a few thousand miles and it will be spinning free.

 

[anthonymtz]

They are all the same, the part number for the oem Motorcraft one is GR-821, you said you have a 05 4.0 so you will have a 3G alternator, the 6G is in the bigger engine's, the 3G and 6G both use the same voltage regulator. I would recommend only Motorcraft for durability. Good luck!

 

[fizzer]

Excellent, thank you for the quick responses.

I am not sure why I am getting the error code since my PCM must be okay as I do not get the code with the new alternator.

When my old alternator failed I only had 12.6V at my battery with the vehicle running so clearly it was not working. When I took the old brushes out one of them was right down to the metal clip. I figured this was the problem so I replaced the brushes and now I get 14.2V so it seems this has solved the problem. Unfortunately I have this pesky error code. I think the rectifier is okay as I checked continuity between the B+ terminal and the alternator body and I get infinity in one direction and 3.53MOhms in the other. This indicates to me that the rectifier diodes are working. The only other thing I can think of is the regulator but it seems that it should be okay since clearing the signal is turning the alternator on and it seems to be doing its job regulating the voltage. I did notice that with the new alternator the voltage is around 14.5V so a little higher than the old alternator.

I think I will try replacing the regulator but if anybody has any other suggestions I would love to hear them.

thank you.

 

[Number4]

The alternator will put out from 13.9 - 14.5 depending on loads under normal operating scenarios. Also depending on components. So I wouldn't worry about the two different outputs.

Yours should be a 3G. It was a 4G years prior.

I'd thought about going through these guys at one point.

https://alternatorstarterrebuildkits.com/product/3g8519/