Hello all from Southern Vermont!
Kudos on a great board!

I have a 2001 F150 S-crew XLT. 5.4, auto, basic power package. 91000 miles so far. I've only had 2 minor problems with it (until now.) The first is the intermittent odometer LED, the solution to which I hope I've found here! (With all these bad solder joints you'd think Ford would pick up the tab on this repair!) Secondly, I had to replace 2 coils.

My truck sat for a week while my wife and I were away. Last Friday, while driving to work, I noticed the battery light had come on. The indicator light isn't terribly bright so I likely missed it while driving during daylight hours... Dash gauges showed nothing amiss. If I revved the truck in neutral the light would go out. Hmmmm.... On the trip home (less than 15 miles) everything electrical started failing, radio, windows, etc. Less than a mile from home it entered "limp" mode, barely able to pull 20 MPH. Upon arriving home I checked battery voltage, turned up 9.4VDC. I put a charger on the battery and let it cook for a few hours, bringing my terminal voltage back to 12.5. I fired up the truck and hooked up my meter. It showed a quick voltage loss, so the troubleshooting began.

I'd installed a new Interstate battery last fall, nearly a year to the day, so I initially ruled that out. I went through both fuse panels, under dash and under hood, and checked the fusible links. All apppeared fine. Terminal connections all looked good, but I cleaned & tightened 'em all the same. The alternator was the next of my likely suspects, and under inspection I noted some black soot on the casing. I pulled the serpentine belt and noticed it was at it's service limit according to the handy indicator on the tensioner. There was some cracks, too. I'd noticed some belt squeal upon hard acceleration of late, so it was partly suspect, as well. I then removed the alternator and took it to the local Autozone for bench testing.

According to their machine the alternator is working OK. It passed all three tests with flying colors. While I was there I picked up a new serpentine belt, still thinking that it might be part of the problem, and headed home to put everything back together. After reassembly the battery light came back on quickly. While running, with voltmeter attached, it showed a loss of .2 volts per minute. Could it be the battery? With fingers crossed I changed out the battery from my 91 Nissan mudder and fired it up. Still the same problem!?!

This one's got me stumped. I'm thinking that the alternator actually needs to be replaced. My first question : Is there a part other than the voltage regulator on the back of the alternator which controls voltage output? Second question : What's the likelyhood that the alternator really is bad?

In scouring the posts before posting my own I noted very few users replaced alternators, and the few that have note their replacement well over 100,000 miles - usually around 115 - 130K.

Any help is appreciated, and I'll be sure to post how I rectify (electrical pun intended) the problem.

Thanks!
Tom

P.S. - I should also note that I cleaned and reassembled all connectors with dilectric grease upon reassembly. I'm going to pick up a reman alternator tonight and try a swap (once wifey gets home with her Pathy) fingers crossed!
T

 

I would recommend replacing the alternator. At higher RPS's the brushes tend to start bouncing which causes the light to come on. If the alternator is not replaced/repaired in a timely manner it will also cause the battery to fail. You should be able to replace it for about $135.00.

 

here's a big thumbs down to my local Autozone.... or at least the tool that tested my alternator! I went on my instinct and replaced it with a Motorcraft reman, limited lifetime warranty, for less than $140.00 Everything is now working as it should. Oh well, at least I had a good reason NOT to go to work, and just like a bad day fishing, working on your truck in the rain, outside, is still better than a good day at work!

 

I just stumbled across this post of mine that I'd forgotten from so long ago. In the nearly three years that have past I'm on my 3rd re-manufactured alternator from Autozone. The first two have managed an average of 8000 miles each. I'm to the point I can change one out in less than 20 minutes. Thank goodness for their limited lifetime guarantee!!!