Charging system question

[KJT]

Hello all, have a 2002 f 250 PSD. I noticed at night the head lights are dim when idleing. When engine speed increase the intensity of the headlights increase as well. A digital volt meter on the battery when ideling is at 13.2 volts. At 1500 rpm the voltage increases to 14.2 volts.
The voltage from the rear of the alternator when running is 12.6 volts. Both batteries read approx 12.7 volts when vehicle is off.

Is this a problem?? A faulty alternator?? Voltage regulator?? Dont really want to take it to Ford and pay $200.00 to get it checked!!

 

[RenoF250]

The batteries should be at 13.8V on their own and the alternator should charge to 14.2V. Sounds like maybe on of the cells in the batteries is dead and the alternator has to pull it up. If you have an 02 it is probably about time to think about new batteries anyway, that would be my first guess.

 

[redpsd]

How has the truck started? One of the first signs of batteries going out will be the truck turning over fine but not starting. There isn't enough "umph" in the batteries to fire the injectors.

red

 

[KJT]

charging system problem

Thanks for the help, batteries are a few months old. Truck starts with plenty of cranking power and starts right up. I will double check the battery voltage. Alternator definately not at 14.2 volts at idle. seems to fluctuate between 12.5 and 13.6 when idleing.

 

[dmftoy1]

Does it happen all the time or only when you initially start it up? When you first start it (if it's cold out) the glow plugs stay lit for about 2-3 minutes and there's a noticeable change in the brightness and the ammeter on mine jumps from 11.8-12.2 up to 14.2.

Probably not what you're seeing but I just thought I'd throw it out there.

Have a good one,
Dave

 

[KJT]

I have noticed the same thing on a cold start. However even when engine is at operating temp. headlights still dim at idle. The reading at the batteries varies even when warm. Have seen 11.6 volts, 12.6, 13.5 and 14.2 volts.
Each time I check voltage, the voltage remains constant for that check. When I turn off the engine and wait a minute and restart it again I have a different voltage (all accessories off during checks). Im leaning towards an defective alternator??? What do you think??

 

[dmftoy1]

I'm not smart enough to say one way or another. I'll see if I can find you the troubleshooting pages out of the factory manual. That's where I would start.

Have a good one,
Dave

 

[dmftoy1]

Ok, here's a link that will hopefully give you the troubleshooting methodology and pinpoint tests:

http://www.fahringer.net/x/charging.htm

Have a good one,
Dave

 

[ryaneverk2]

Check the battery voltage when the truck is not started, then start the truck and recheck voltage. Whatever the voltage was before it was started, it should be about 1.5-2 volts more now that the alternator is doing its job. If you don't get an increase in volts, it's most likely an alternator problem of some sort.

This is a test my grandfather taught me, and it seems to hold true as far as I've seen.

 

[KJT]

Thanks everyone for your help, turned out to be a defective alternator. R & R'd the alternator and problem was solved.