Super Duty charging voltage

[tech10002]

Does anybody know what the nominal voltage should be on an 05 Super Duty? My cousin's truck has been getting harder to start, and the bats finally went completely yesterday. We replaced both bats, and the voltage I measured seems pretty low. Most vehicles I've worked on show at least 13V at idle, but his only runs 12.4 or so until you rev the engine up. Then it goes in the 13s.

There's no battery light on, but I'm just concerned something might be wrong. That voltage sounds awfully weak.

[redstroker_2002]

That seems week to me also. My truck runs the 14's after reved up. 13ish at idle.

[bigd4x4]

Check it again after it runs for a while. Maybe the new batteries where low and that is the most the alternator can do while supplying a lot of current.

[tech10002]

I don't think they were low. They were both reading 12.8 volts when I installed them, and they started the truck instantly, but I will tell him to check it after he drives it more. He has the big extended warranty, so it should cover the alternator if it ends up being bad.

[GGOODMAN]

When My alt went i got no lights... it just died. Put in new batts, ran for three days then same thing. New Alt and all is well. your spot on it should be putting out 13-14vlt. discount auto was where i got mine. $500 for the ford one with a two year waranty or $250 for the rebuilt with a lifetime waranty. Choice was easy for me.

[SCUFFY828]

one thing to remember is if you check it just as soon as you fire it off , the glow plugs could still be on

[tech10002]

I did notice that it would drop down to around 10 volts right after it started, but after 10 seconds or so, it would come back up to 12.5 and raise to like 13.2 if you revved the motor.

How much current do the glow plugs pull?

[SCUFFY828]

enough to make that couple of volt difference,i would check it after being driven a bit and batteries were charged

[tech10002]

It must have been the glow plugs still on and the new batteries. I called him today, and he said it was running 13.6-13.7 at idle, so it appears the batteries were the only problem.

Thanks