This problem is in my 2002 4.6L Town Car, but I figured someone in here might know.

Last night my battery light stayed on when I started the car, I reved it up a bit, and it went away. As I was getting on the freeway, it came on again, and then went away.
This morning I took some measurements. With the engine off the battery was about 11.7 volts. With the engine on the alternator was 14.09 and the battery was fluctuating between 14.00 and 14.09. While I was tinkering with it, the battery light went on and off a few times. I swapped the battery from my truck into the Lincoln which was 11.4 with the engine off and fluctuating at 13.98-14.04 with the engine on. I started to drive to work and then the battery light came on again. I turned around to get the truck, and the battery light stayed on for the entire 10-15 minute ride home. When I parked it I took some measurements again and got about the same figures as before.

What do you guys think this might be? I've had the car for a little over a year and this is the first time I've had any problems with it, so I'm not to well versed on the 4.6 modular yet. I would have measured amps, but the amp function on my DVM seems to be broken.

Thanks! I'm really diein' here because my drive to work is about an hour through the middle of nowhere and my truck (69 F100) really isn't ready for long drives yet. If you don't hear from me again, it's probably because I got stuck out on some farm road and am surviving on strawberries and coyote.

 

The alternator is getting ready to quit.

 

So even though it was putting out 14Vdc you think it's still on it's way out? I was kinda thinking the same thing, but the 14Vdc really confused me. I think what I need to do is load down the electrical system and see if I'm still getting 14Vdc.

Either way, do you guys think it's safe to drive for 200-300 more miles or should I just park it until the new alt comes in? I'd just drive the truck, but like I said before it really deserves a lot more attention before it ventures too far from home. Not to mention 8mpg and a factory recommended top speed of 70mph (driving it around town sure is a pleasure though!).

 

Well I drove it to work today, light going on and off the whole time, and when I got to work the voltage had dropped to 13.5 and the battery was at like 12.88 (when running). There is usually only a .01Vdc drop between the alt and battery, so the .62Vdc drop tells me that it was pulling juice from the battery for at least part of the trip. Guess I'll be buying a new alt tomorrow morning. Let's just hope I can make it 50 miles home, and if not, let's hope it dies somewhere with cell reception!

Does anyone know of these are user-rebuildable? If so, which parts should I order? Any special tools required? I've rebuilt and repaired more electric motors than I care to admit, so I should be able to figure an alternator out.

 

This forum is really slow, but I figured I'd post an update anyway just to add to the knowledge base.

Anyway, I replaced the alternator and belt last night. It was pretty straight forward, the belt was the hardest part but I found keeping the alternator loose and tilting it forward and then using a crow bar to hold back the tensioner relieved enough pressure to slip the belt on with ease. It was only about 10 minutes of actual work once you subtract setup, figuring out the belt trick, and clean up. Oh, and I took photos of the belt layout before taking the old one off. The battery light went away, and the power window and seat motors work faster than even a year ago when I bought it (at 75k miles, now has 100k miles). The stereo even sounds crisper. I think this shows that the alternator had been slowly dieing the past year.

EDIT: Oh, and I chose not to rebuild it because I really needed the car back on the road and the only rebuild kits I found were mail order. The local Kragen had the parts in stock, so I just went with them. It was about $170 for a rebuilt Autolite alt and $20 for a Goodyear belt.

 

Glad you figured it out. Nothing worse than getting stranded in the middle of nowhere with a dead car. On a side note, your F100 looks like a really fun truck to ride around in!

 

Yeah, it is. I can't wait to get it back to tip top shape. The truck sat for a long time before I bought it, so everything rubber dried out. Basically everything leaks, and the suspension bushings are real loose. Once I get that done, it should be good to go for more frequent driving. The engine it self runs great though. Right now I just drive it on the weekends and such. Took it to the lumber yard this weekend and the dump last weekend. Hauls a bed full of wood and masonry without blinking an eye (unlike a 4cyl Toyota I once had where you could feel every pound you put in the bed).