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Alt. Overcharging

RAD Merc SVT

CEG'er
Joined
Aug 2, 2010
Messages
489
Location
Phoenix, Arizona
99 Mercury Mystique 3L port-matched NPG tune, Optima Yellow Top, sound system.

Here is the scenario. About three weeks ago my amp kept turning on and off randomly, I found it was going into protection mode because it was seeing over 16v. I measured voltage at the battery. Engine off: 13.2v, engine idle: 15.5-16.1v engine idle with sound system disconnected (in case it was creating a heavy load) still 15.5-16v.

Battery is good, I assumed the voltage regulator or something in the alt. was bad so I replaced alt. with a new one. Started it up measured voltage still 15.5v and my amp is still turning off randomly so it's still getting above 16v. I had the old one tested and it failed anyways making me think the new alternator/regulator is bad. Before I pull it off and have it tested I was wondering if anybody has any ideas on what else it could be. I think it's weird that both alternators are doing the exact same thing. So the new one is in now with the same problem but now the charging system light is on and it wasn't before.

On another note after I built the 3L and put it in my datalogs show 13.8v so it was working

Thanks for the help I've been struggling with this one for a while
 
I would guess you got an alternator with a bad regulator. Nothing outside of your regulator could cause you to have high charging voltage.
 
Thats what I thought but figured I would ask before I pulled it again. I am going to test it tonight when I get a chance to get under it. I will update then
 
Tested it and I believe circuit 20 is bad. (cable from alt. to starter) So my question now is if the fusible link burnt out, would that cause an overcharging problem? Wouldn't it just not charge at all because it has no connection to the battery? I found that cable resting on my headers and exposed so it must be shorting and fusible link must be burnt. moved it away from headers still 16.3v
 
I'll buy the alt off you!!!!! :)

Seriously though, if you are getting that voltage at your battery your cable (alt to starter to battery) is fine.
It is the alternator, the regulator and what not is irregular.
 
weird as hell... it was the alt to starter to battery circuit. I took out the maxi fuse assuming it was blown and it was still good. So I just cleaned the piss out of all the connections on the battery and maxi fuse, moved the cable that was melting on the headers away from the headers and it was charging at 14.5v and I just datalogged it again to fix an idle problem and it said bat. voltage was 13.8v. But my battery light is still on but I have a trouble shooting tree for that as well so that will be next week. But charging is good.
 
I think that is whats going on with my alternator. My head unit turns off randomly, but I'm getting other strange issues. I should have time this weekend to check my connections to and from the alternator.
 
My guess: Altenator is still good. Bridge rectifier in the regulator is breaking down cause the voltage to be high. This happened to one of my cars. Is your battery light on at low rpms but not at high? If not my best guess says this will start happening, and continually get worse. This problem ended up damaging my PCMs EGR functions, when the voltage starts getting higher and higher you will start to fry circuits. I would get in there and swap the regulator. Motorcraft ones are about 30$.

edit: Just saw you already swapped the alt/reg, I skimmed this originally, just seemed exactly like my scenario. So my post is relatively pointless but still good info for another poor soul whos alt is failing.
 
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