Question Low Voltage on start up: Battery light on

[chromedom]

Hi, I'm another new guy. But this site has helped me alot. My 2004 F350 6.0L starts fine and my voltmeter (dash mount) says about 12.2 volts after starting. Normally after a few min. it shows about 14.7 volts. Which I think is the glow plugs drawing it down for a short time. Now when I start it it goes to 12.2 volts, the battery light comes on and stays on for about 15min. After that the voltage returns to 14.7 and the battery light goes off. It only does it after the truck sits a long time. Any suggestions before I go to the dealer for a song and dance?

 

[DaveBen]

Batteries? I have replaced mine a few months ago. Same year of truck.

Dave

 

[chromedom]

Thanks for the reply. I should of added that both batteries and alt were replaced in the last few months for other reasons. The battries were first to repair the "won't start when below 32 deg." problem. Than when that didn't fix it they replaced the Alt which I didn't see the connection because of the proper voltage output. I think it maybe something else being that I can almost tell when the voltage is going to come up. 15 min. and it comes up no problem. It's like clockwork. Is their something with the glow plugs that stays on until the engine come up to temp?

 

[BIG JOE]

Try cleaning up the Battery connections and cables ? Real Good ?

Give all the "under the hood" Grounds a re-tightening ?

 

[DaveBen]

The glow plug cycle to start and go off until the key it turned on again and it is cold. I had a question on my alternator and I bought a plug in voltage guage. I plug it into the power port on the dash and can keep an eye on it. I don't remember where it got it.

Dave

 

[Bolt]

I have an Isspro volt meter wired straight to one of the batteries, and it's my opinion that the voltage drop for the first minute of startup is because the vacuum pump is running. You can hear it running over on the passenger fender well. I have wondered if you could wire it in such a way to get it to not run until the motor is actually running, you would save some amps for the glow plugs and cranking, and not waste them on vacuum before it's running. BTW, I haven't ever pulled the fuse to see if thats the cause of the voltage drop, so it's just an opinion right now.
But yeah, in your application it does sound like your batteries are nearing their end.

 

[DaveBen]

The vacuum pump in these trucks is small and does not draw a lot of power like the earlier trucks. If you have a shorted glow plug (failed) that would draw a lot of power. Ohm them out, you shoud see from .5 to 5 ohms, or something like it.

Dave

 

[snicklas]

Does this truck kill the batteries if it sits for a day or two? Mine will randomly kill the batteries if I let it sit.... sometimes overnight. Or I can go weeks and it is fine? Or are you just seeing this on startup, and it will start with this condition, correct? Also, my batteries are only a year and a half old..... new NAPA's.....

 

[DaveBen]

It should go weeks at least. If you are killing batteries over night, you have a wiring problem. It is NOT the glow plugs or the vacuum pump.

Dave

 

[chromedom]

My batteries were replaced last december along with the alt. Nope it don't die after a few days. Got the truck back from dealer today with no problem found. As DaveBen thinks on a shorted glow plug, that was my suspision back in december.