I'm stumped. My truck is a 2006 F150 XL 4wd 4.6L.

Intermittently, the interior lights and headlights will dim, sometimes gradually, sometimes instantly. While doing this, the charging gauge doesn't move. Without reason, it will just return to normal.
Other times, and this is becoming a concern, interior and headlights will spike out VERY brightly, alt. gauge spikes to almost pegged. What a THINK is the alternator will often start grinding during this, but it's not every time.

I changed the alternator, problem returned. Changed the battery, problem returned. I've checked connections, but given the voltage spikes, I doubt that's the issue. I've cycled heat and AC, headlights, any electical draw I could think of with no effect.


I'm not sure where to look next.

On the up-side, since I had the battery out anyway, I changed the IWE solenoid while I was there. One less thing to worry about, if the charging system wasn't going nuts..

 

I would trace the positive battery cable down to the starter solonoid and then on from there to look for a place whare it may be shorting out to ground. If that all looked good, then check all the ground cables you can find. These modern rigs have what they call a ground loop, where they no longer depend on fasteners to keep everything grounded but instead have everything grounded via cables. You wouldn't be looking for shorts here, but for loose connections.

 

OK, I'll start there. Thanks.

 

Don't you hate these kinds of problems? I am guessing this happens only while moving and you are unable to duplicate it while just sitting trying to load the system. If that is the case, I would be thinking loose connection somewhere and they are not always easy to find. I would not replace any more parts at this stage in your investigation.

Steve

 

Would a bad/loose connection also cause the over-charging spikes I'm seeing also? Didn't think it would..

 

I dont think a loose connection would cause an over charge reading either, if any change in amp. it would be a decrease with loose connections. A bad ground or shorted out line somewhere could be causeing the dimming but not an off and on scenario like you said. If there was a short it would be poping fuses left and right most likely. It seems to me its more of a relay type of problem, . Since it seems to be able to come and go at not specific patern. Im not by any means an electrician, but thats just what it seems like to me.
Fords are famous for these electrical 'ghosts', as my father always said. Dont you love it

 

Hi,

Here are my thoughts on the loose connection having researched this problem all over the Internet. The alternator's regulator has to constantly respond to the demand being placed on it. The alternator is the only thing I can think of that can produce a higher than normal voltage and a number of folks have reported similar problems on FTE that have not been resolved by replacing alternators, batteries, etc. On most vehicles, the regulator is internal to the alternator and the alternator in this case has been replaced.

The PCM can cause an alternator not to produce voltage, but as I understand it, it's only role is to turn the regualtor off and on. Not tell the the regulator how much current to produce.

If here is a brief break in a connection, not a short. I believe the alternator will react by rapidly by increasing voltage, then with the next bump in the road, decrease output, etc.

I always tend to go with the things I see happen the most often, and my own style of working is never to put a new part in anything until I am sure it is causing the problem.

I am not at all sure in this case I am correct, but if the only way to replicate the problem is with the vehicle in motion, my thinking is something must be loose.

I could certainly be wrong here as I do not know this specific charging system. I just routinely see so many parts replaced in the name of loose connections and bad grounds, that is my first thought.

Good luck in tracking this problem down. I know it can be tough!

Steve

 

corrosion on cables?
double check and clean all grounds

 

Only thing I can think of is the wiring to the voltage regulator.

 

Well, based on advice here, I checked every connection between the batt, alt, starter, ect. Only thing out of the ordinary I found was a little road salt built up in the fusible link box. Nothing bad, just a little dust to shake out. While I was there, I taped a few of those connections up better than the factory had, hopefully limiting future problems.
Meanwhile, while talking to a friend, he reminded me of a similar issue he had, that turned out to be a short in the trailer plug wiring.
So, I checked that, and the 4 wire plug cap WAS off, there was quite a bit of corrosion in the taillight socket, and looked like it may have been arcing there. So I cleaned that up, coated it with di-electric grease and reinstalled the cap securely.

Hopefully, that last one was the culprit, but I'm not convinced. Just have to wait and see if it acts up again...

 

Figured I'd update this thread in case anybody else ever runs into this.

It ended up being a broken wire in the harness between the Alt. and the PCM. Took a fresh pair of eyes to find it, I never would have. Took it to a local shop I trust, he found it after a few hours of testing. The repair bill was far cheaper than the starter, alternator and battery I put on the truck for what now proves to be no apparent reason, but, I'll just chalk those parts up to cheap insurance.

Just one of those times that I'd gotten too frustrated with chasing wires, and the break could have jumped up and bit me, I wouldn't have noticed it until a part fell off or caught fire.

 

Thanks for taking the time to up-date us on your trouble. I had forgotten all about your post. Was the broken wire wrapped up in a harness, or was it unwrapped?

 

It was just inside the harness near the firewall leading up to the PCM.
It was shorting out, and got to the point that it was only charging around 13V.
When the wire intermittently made good contact, it would send the alternator into overtime, hence the noises and light show.