I found a few posts on this one but no one has posted a solution.
I just installed a supercharger and with a new tune from Troyer performance I am now pulling higher RPMs. When the RPMs go over 4700, the battery light comes on, at first dimly then brighter as I approach my 5200 RPM shift point. It then goes out as soon as the RPMs drop back down.
I have a Gatorback belt and it is really tight. I have a brand new battery, replaced this spring and I replaced the Alternator about 2 years ago.
Any ideas? I have a 97 so there’s no electronic diagnosis ability unless it throws a code. There is no code.
Any help would be greatly appreciated.
Thanks.

 

If the belt is in fact tight through the high Rpm's, take the alternator off and go and have it bench tested. Have you watched the belt while someone rev's the belt? Are you absolutely sure you have the correct gatorback? They have a habit of being deceptively tight except for when you goose it. I went back to the standard Kelley Springfield in my 97 because my Gatorback would slip if moist.

 

Throttle, thanks for the reply.
I'm sure about the belt. I have to pull my tensioner all the way to the stop just to get it on. Even if it was slipping, it would have to slip a lot to make the ALT not charge and I should smell some belt burning.
Testing the ALT probably wont work since I don't think anyone will be able to spin it to 5000 RPM in a tester. I am more wondering if this is a Regulator problem and if I need to worry about it. I don't want to burn anything up. I’m wondering if the Regulator is replaceable.

 

Another thing you can try is set a volt meter to DC and cross over the battery terminals. Have someone hold the throttle at 5000-5500 and check to see if it's lower than 13.5. If it decreases under that kind of load, it's probably your regulator. Call Automotive Generator & Starter (410) 523-2942 to see what they recommend.

 

The problem with youre alt. is probly in the brushes either one of the spring are brocken or week, the brushes are worne, or even a dirty armeture. I believe the brushes can be accessed by removing the alt and then removing the regulator. Or take it to a rep. alt shop. this would not hurt anything, but the problem is not going to get any better, and will probly let you down at the worst time.

 

mine did the same thing before the alt went out.i tore it down and one of the brushes was really worn and the other was comepletely gone.i don't know of any kits to rebuild these alternators,i asked on here if anybody knew of one but nobody said anything,cause i don't wanna pay another 200 bucks (and that was after the core charge and gettin the alt at cost) so if anybody does know of a rebuild kit i'd apprecate you lettin me know.its not hard to tear the alt down,as long as you have some automotive knowledge and common sense that is.you also might wanna go to a 130 amp alternator if you don't have one.that supercharger will draw alot more power than a n/a engine

 

I agree,, bad alternator.. Have the same thing happen with alot of our fleet vehicles. Dont wait too long to fix it if you rev it high alot,, the alternator puts out alot of spikes when it is doing this and is rough on electronics.

 

way fast whitey,
You can find brushes here

https://www.rockauto.com/applet3.html

Since I can find both brushes and voltage regulators, I will try the regulator first, then the brushes if need be. I was just going to go with a new ALT because the price of the regulator is so high (about $50) but since the brushes are also available and there seems to be no play in the bearings then there is no reason not to go ahead and try to fix this one.

 

WLF,

I just checked........if you go to www.car-part.com you will find 2002 and 2003 f150 4.6 altenators for $40 and $50 bucks in your home state. Good luck!

oops!

 

iron horse,
Thanks that's a nice tip. I contacted NAPA where I bought the ALT and they will test it on the truck and replace if bad. I told then it only happened at 5000 rpm and they were fine with that.
I'll see.

Also in your link you put in an x-tra , so it will not work but worked just fine with the , removed

http://www.car-part.com/

 

Just as a follow-up, I found my receipt for the NAPA alternator I bought in 2000. I took the truck over to NAPA yesterday and they tested it on the truck. It was only putting out 13.5 volts. Some would have said this is fine. NAPA replaced the alternator under warrantee without any hassle.
The new ALT is on and no lights on the dash at any RPM.

 

WLF,

The same thing happens in my truck. Battery light comes on at high RPMs. I did what Way Fast Witey suggested and replaced the brushes. One of them was significantly more warn than the other. When I looked at the rotor inside the alternator, I noticed one of the two copper slides that the brushes rub on was very slightly out of round. You can only tell if you spin the alternator with your finger running in the track. I believe the tiny bump at high RPMs causes the brush to vibrate enough to prevent a good connection. Replacing the brushes works because the springs press down harder when the brushes are new, but that's just a temporary fix.

Anyway, I might see if I can find a buddy with a lathe I can borrow. That should be a free fix. I'm not sure the rotor can be replaced independently, but if I was going to inspect a rebuilt rotor again, I would definitely take the brushes out and make sure those two slides are perfectly round. Lots of people have this problem and it may be possible that many alternators have this defect.

G.