alternator issues

romois9

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On my 04 3.9 alternator only puts out 12.56 volts. So I got a new alternator, same issue. Even swapped batteries. I can run and start it no problem as longs as I don't run headlights. I was hoping the new alternator would fix the problem but it has the same exact problem still. Any ideas? Already checked the alternator sense fuse.
 
On my 04 3.9 alternator only puts out 12.56 volts. So I got a new alternator, same issue. Even swapped batteries. I can run and start it no problem as longs as I don't run headlights. I was hoping the new alternator would fix the problem but it has the same exact problem still. Any ideas? Already checked the alternator sense fuse.

Motorcraft or aftermarket alternator? The LSes electronics don't play well with most non-OEM electronic parts. There is a whole discussion on this.....
 
oem alt

Motorcraft or aftermarket alternator? The LSes electronics don't play well with most non-OEM electronic parts. There is a whole discussion on this.....
Well the alternator I took off was doing the exact same thing, it was OEM
 
Your answer is unclear. Yes, the original was OEM. Is the replacement OEM?
It's easy to see a new non-oem alternator have the same symptoms as an old failed OEM alternator. The non-OEM alternators don't use the correct voltage regulator/controller.
 
Your answer is unclear. Yes, the original was OEM. Is the replacement OEM?
It's easy to see a new non-oem alternator have the same symptoms as an old failed OEM alternator. The non-OEM alternators don't use the correct voltage regulator/controller.
It's a motorcraft, one issue was a ground it boost the volts up to 13 but doesn't drain with the lights on. My car has never produced more than 13.4 volts even when I first got it.
 
what are you using to test the voltage, and exactly how are you checking it?
 
Even with another meter it shows the same. I didn't put a new battery in it so that could be an issue. Does anyone else have an alternator ground issue with theirs
 
Even with another meter it shows the same. I didn't put a new battery in it so that could be an issue. Does anyone else have an alternator ground issue with theirs

A dead/failing battery can kill an alternator and vice versa........
 
Are they internal regulated or external

I believe the PCM controls the output. Honestly, there's more information in the H.O. alternator thread on how the alternator works and it's relationship with the PCM between the generations.
 
I believe the PCM controls the output. Honestly, there's more information in the H.O. alternator thread on how the alternator works and it's relationship with the PCM between the generations.

That's 1st gen, 2nd gen doesn't have that problem.

Replace the battery and alternator together, should be good after that. If you suspect a grounding problem, when you replace them clean and sand all ground connection points until you see shiny metal on both the wire and the metal it's bolted to. Run the wiring with your hand too, to make sure there isn't any damage to it.
 
Well my alternator isnt getting a good ground. Does that make any sense?

well the alternator bolts to the engine, so that is a pretty good ground (unless the alternator is not tight and flopping around) you can check the engine ground (or just add another one)


also since it wasnt a new battery that you tried, where did you get it from? what's its age? how was it being stored? maybe that battery is crap too...
 
I had it laying around for a couple of months, when I took it from work and tested it showed 12.4 volts and 850+ cca optima. It was made 4/12 just like the 66 series I swapped it with.
 
Your battery is toast. Replace it first. Your alternator might be fine but can't keep up with the load the bad battery is putting on it and the headlights, but can keep up with just the battery.
 

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