Anyone ever have this happen?

The alternator seems to cut out when I rev the truck's engine up or put the engine under load. It will do this with the truck in gear (usually when passing car or accelerating) as well as with the truck in neutral and revving the engine up a little.

What could be the most likely cause of this discharging business?

I was thinking that the belt could be slipping on the alternator's pulley or the bearings in the alternator might be on their way out. At this time I'm not hearing any squealing or unnatural sounds from under the hood.

The truck is a 1999 with about 112k miles on it. Still has the original everything under the hood except battery and a couple of replaced sensors.

 

I had a 99 Expy that battery light came on when you hit over 3000. Ford replaced in but I remember it was something to do with the volt regualtor. High Rev something but cause no drivablity issues. I could be something easy like a lose wires or some corrosion on some wires.

 

Take the truck to a parts store (AutoZone, O'Rielly) and have them do a free check of your charging system. Let us know what you find out.

 

Is it possible that the output wire from the alternator is getting 'flexed' out of position and loses connectivity? I had a problem with my alternator whenever I accelerated. Of course, I had taken it apart, and found I had left a connector loose internal to the alternator.
The brushes could be losing their connection to the slip rings at higher rpm's.
tom

 

at night when you have your headlights on, when you reach a certain speed, maybe about 3k rpm, do you see your headlights and dash lights dim a little bit. i had this problem a few months ago with 114k miles on the original alternator. looking around online i saw other people had this problem, and their problem was the alternator brushes. after years of use they had worn down, and when the engine was spinning too fast, they would no longer make contact. then at these high engine speeds, the battery would only be supply the about 12.6V is has by itself. in other words, the alternator was not charging the battery due to a temporarily broken connection so the battery could not get the full about 14V if the alternator was connected.

if this is your problem you can replace just the brush assembly on the alternator, about 15 bucks. however if you have a 4cylinder like me i am not sure if these parts are available aftermarket for those alts or if the brush assemblies from the other engines fit the alternator in the 4cyl. napa makes this part, maybe others too. i decided to just replace the whole alt because i needed my truck and couldn't wait a week for shipping.

 

Thanks for the input!

When the engine is under load, my dashboard gages show the drop in charging power. Like I mentioned, revving up the engine in neutral will also cause these symptoms.

I'm going to look at it this during the weekend. It's most likely a tired alternator from what 12-year old alternators tend to do.

 

I still have the factory in my Sable, with 250k on the clock. I did replace the brushes at about 180k and tried to clean and lube the rear needle bearing. Couldn't get the front taken apart to lube the front bearing, but last summer was able to squeegee bearing grease past the seal using my finger. A very dry ball bearing now seemed lubed once again.
When I took the old brushes out, they were not totally worn down, and were within factory limits. I would inspect all the wiring from the alternator to the regulator, looking for corrosion or spots where the wire flexed as the engine loaded & unloaded. Check all push-on connectors. The regulator in my Sable had been 'cleaned' when my brother washed the engine at a self-serve car wash, making some of the smoke leak out unbeknownst to me. The only symptom was the idle when put back into park. Still charged the battery, but some stuff was really blown away.
Regulators are a lot cheaper than "re-built" alternators in most instances. Could be a cheap and easy 'parts shotgun'.
tom

 

I had the exact same problem on my 99 F-150. Replaced the alternator, good as new.

 

New alternator did the trick.

$100 and some change from Advance Auto Parts. There some good coupons online that can save a good chunk of money. I got $30 off a $125 item.

Thanks for the input guys!!