I have a 98 F150 4.6L and have been noticing the charge idiot light coming on at 4000+ RPM. I don't typically drive at 4000+ RPM but when the tach swings past 4K the lamp lights up. I have recently (few months ago) replaced the sepertine belt.
any ideas???
thanks
-tom

 

I was going to say it might be the belt, but you changed that.

My knowledge database doesn't cover a light coming on at high rpms. Usually, the light comes on at low rpms. Can't wait to see what ideas others come up with on this one.

 

Mine started doing that too. I didn't notice it until I installed my chip, but now that I think about it, I had changed the belt to a Goodyear Gatorback at the same time. Hopefully someone has some ideas...

 

Maybe the Alternator is putting out too much voltage.

The stuff I have read on the Post 98 HEC, shows 16.1 and up as a high voltage indication.

Try hooking a set of wires to the battery, run them into the cab, and put a volt meter on them that has a high limit hold function ( Fuke meters hava this ). Drive it up to 4,000 RPM and see what the voltage is on it, or have a friend sitting in the pass seat read the voltage at 4,000 RPM and see what it is.

If you are putting out more then 16 V you are trying to boil the battey acid

This seems like the easy way to test it, else take out the alternator and have a shop you trust test it.

If the voltage regulator on the output side of the alternator is shot this can happen.

Here is the other thread on the topic, but having it happen at 3500 RPM:
https://www.f150online.com/forums/sh...hreadid=117970

Good luck.

Steve