Ok, I posted question about the issue with air brakes yesterday & now this happened to me today. Driving at highway speed, my volts with jump from 14 down to 12 & then back up again. At the longest, it will drop to 12 for a minute or so & then jump back up to 14. I don't have headlights, radio, or heater on when this happens. I just got a new alternator put on this summer.
Interesting, what happens if you turn the lights and heater on when it drops to 12v? I'd check all the battery terminals for tightness or signs of arcing, and especially the alternator terminals since it was replaced recently. Once saw a + battery cable rub and then arc on the flange of the frame, arced half way through each! Only did the voltage drop thing for a short time before it was discovered.
This happened to me before 2x. Once it was the battery ground and the other time was the alternator ground. Check that your grounds are good and clean.
Does the engine have a grid heater (or intake heater... same thing, different name)?
My service truck did that. /found a loose positive on the starter.
Nothing happens, it still remains @ 12v
I don't think so, its an old 3406B CAT
When you are getting 14v your alternator is charging, When you get 12v, that is your battery voltage and your alternator has stopped charging. Check all the connections, cables and grounds. If that isn't it sounds like your regulator is bad.
Found a kinda loose connection of positive cable @ alternator. Tightened it up & we will see. Haven't had the chance to drive the truck since finding the problem. All other things looked good at starter & in the battery box.
External regulator? Behind the air cleaner? All of my L9000/L8000s do this at times, I dont really care as long as it charges.
I will check it out when I get to work on the 27th. Never had any problems with this since I've been driving the truck in 2011
Some do. If it does the 12v-14v "pulsing" is when the heater is on and then off... it sucks quite a bit of power.
The heater didn't change anything with the voltage. I was in the truck all day Friday & it never happened, looks like it was the slightly lose positive cable to alternator.
At the beginning of January, I had my blower motor & squirrel cage grenade on me & I wonder if a blower motor about to die actually did play a little role in the bouncing voltage. The shop had one helluva time find a squirrel cage for my truck. Apparently for some reason, then blower motor assembly & cage were from the mid 70's so it went from a $30 part to a $250 part. The Ford rep. said he had no idea why that set-up was in the truck.
That positive line you tightened on your alternator runs across to the hot side of your starter. There is a fusable link in that wire near the starter. If you have trouble again down the road check that link. A loose wire on an alternator will deteriorate that link and in time will give you problems.