a124ave

2002 F150 5.4 Tryton motor - SuperCab - Stepside My headlights and Blower fan speed dim at idle and as RPMs go up they become brighter and Fan blower speeds up. The battery gage stays steady as if voltage is not dropping. Is the alternator not regulated by the computer?

02_Black_On_White

have you had the alternator checked?

techrep

iTrader: (1)

Need a new Alt..

a124ave

Will stop at autozone today. I have seen some other post and they talk about the AIC could be the problem. I guess this could be telling comtuter the incorrect RPMs and may be telling the Alternator not to put out the correct voltage. What do you think?

techrep

iTrader: (1)

I don't think the ECM controls what the Alt put's out... there is a voltage regulator built into the Alt.. do you own a multimeter ? very easy to check and see what your problem is...sounds classic bad alt to me...

02_Black_On_White

id check the alternator first

a124ave

Yes I have Meter but maybe I was mistaken I thought that most newer vehicles ALT voltage was regulated by ECM monitoring the RPM's. I guess 2002 isn't newer?

techrep

iTrader: (1)

Take your meter out to the truck and set it on DC voltage...check the voltage on your Battery while the truck is off...should be around 12VDC if your Battery is good...now start your truck and check the voltage while running...should be around 14VDC if the Alt is working properly...

Carcrazygts2

This is half right. A battery can read 12v in standby. True test of a battery is voltage drop and recovery.

To the OP, you need a new alternator.

techrep

iTrader: (1)

told him that already... and what I told him was a way to see if the alt was charging the batt...not how good the batt is.