electrical issue, bad alternator?

[marshall25]

I've got a 2008 F150, 5.4 that a couple of weeks ago while driving the lights went dim, radio shut off and fan slowed down then the front hubs tried locking. It did the twice over a 30 sec time span and lasted for about 5 sec each time. I took it to the dealer (very trusted) and they tested the alt and battery and couldn't find anything wrong. Fast forward to last night I noticed that at an idle the headlights where flickering. I tested voltage at the battery with engine a an idle and the voltage varied between 13.8 to 14.8 and changed so fast that it made it hard to get those numbers. What's going on with this thing? Is it possible that the voltage regulator is going bad and is it internal to the alternator on these?

 

[eljefino]

Maybe the brushes are plumb worn out, can you bonk the alt with your shoe or something to shake it into compliance while it's running?

I'd also (with it off obviously) check the alt mounting bolts for tightness/corrosion and the battery cables, underhood maxifuse box, grounds, etc.

 

[zzyzzx]

How many miles are on it?
I don't trust brushes much past 150K miles.

 

[Plumber]

My 99 Astro acted funny like that. Had a AZ reman alternator was bad.

 

[crazyoildude]

mileage ?

 

[cbear]

Original battery?

 

[marshall25]

72,000 miles, year old battery. I cleaned the terminals on the battery and after that is was showing a solid 14.3 charge at idle.

 

[meep]

def sounds like alt to me. could also be a failing diode or two within it. all vehicle electronics are designed to filter out a bunch of noise and fluctuations, but once you get beyond those filters, control systems can go nuts.