chris_m78

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?

06redlongbed

Probably voltage regulator but could also be a bad ground.

snowborderus

Mine does the same thing. I've had my "check charging system" light come on twice in the past 3 months for about 5 seconds. I've checked the alternator and it comes out good. I'm thinking either regulator or the alternator is just starting to go.

dnlow

Yes, the voltage regulator is internal. I just changed mine out a couple months ago. One of the brushes had worn down to nothing. With the alternator on top of the motor it was very easy to remove and replace. I bought a voltage regulator on line because they were not available locally. It cost about $20 shipped.

Did the battery light come on in the truck? Mine did. My thinking is that the battery is bad rather than the alternator.

chris_m78

no battery light or idiot lights came on, I did clean the battery terminals and retested it, and it was holding a steady 14.6 volts at an idle. At this point I don't know what to do with it.

homer

It's holding 14.6 volts at idle and the headlights are still flickering? Either the voltage is fluctuating faster than your meter can handle or you have something occurring closer to the circuit of the headlamps. Unplug one of the headlamps and measure the voltage at the connector, see if it's the same result.

Ratsan_Fratsan

Sounds like your regulator is intermittent. Check for corroded connectors to the alternatorr. If you find any get those cleaned up first. If you do find any there is a good chance you have more in other places.

What kind of volt meter do you have? As mentioned it may not be fast enough to see the fluctuations.

Mod (Ret.)

Out of couriosity, is your battery the original one? If so, then you're on its 7th year, which is pretty darn good! If not, then how old is it? What brand?

Batteries begin their cycle of death as soon as they are put into service; the good ones can last up to 5 years of trouble free service (you get what you pay for). I'm thinking this is the second battery in your truck, and it's on its 2nd or 3rd year of service(?)

I'd steer more towards the alternator, unless this is the original battery. As others pointed out, you can replace the internal regulator and brushes yourself if you are comfortable with that, or take it to a shop that specializes in alternator overhauls, or buy one already done at your parts store. If you buy a rebuilt alternator, be aware that there are cheap cost rebuilts (A.K.A. "junk"), here's another example of getting what you pay for.

I have also experienced a battery failure after replacing an alternator when my battery was old.

chris_m78

Headlights where not flickering when holding the 14.6 volts at the battery. The battery is one year old, and is a motorcraft. For now I think I'm just going to drive it and see if it does it again.

lewissa81

If the battery terminals were corroded, that could explain the issue you had. I wouldn't be surprised if cleaning them did the trick.