Battery Voltage Values for Cold Starting
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From: Cincy OH
Battery Voltage Values for Cold Starting
I have been having a problem with what I think is a draw on my batteries. At 25 degrees, the truck barely has enough volts to crank. The lights will flicker and recirculate, and eventually (second crank) she will start. Starts fine, no romp, white smoke etc. GPR and GP's are good. AE read 10.1 volts with key to run position, not sure if it is with GP energized or not, as they may have cycled off by the time my AE was connected. Is this low? What should this value read? After it starts, the volts jump to 13.5 or so, at idle. Batteries and alter. all tested good.
I think something is drawing my batteries down whil sitting, as the truck fires fine when cold outside, as long as it has not sat for longer than 8 hours. How do I begin to find a draw?
Could it be that my starter is too weak? If so, how do I test this? It seems fine, but like it is simply not getting enough juice to it.
Thanks for any help!
I think something is drawing my batteries down whil sitting, as the truck fires fine when cold outside, as long as it has not sat for longer than 8 hours. How do I begin to find a draw?
Could it be that my starter is too weak? If so, how do I test this? It seems fine, but like it is simply not getting enough juice to it.
Thanks for any help!
Post Fiend
Joined: Jun 2006
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From: Central, Al
Check the voltage at the batt during cranking should be >10.5
The pcm looks at the EOT sensor and if it is below 131* activates the GP's then it looks at the Baro and IAT and decides how long to rum them. Sometime you can ccyle the key and reactivate them without AE loosing connection but usually I just DMM them manualy.
As far as testing for key off current draw get a DMM capable of reading amperage and clamp around pass red cable. Should be close to 0.1 as the only thing that should be running is KAM and radio clock. Then start removing fuses 1 by 1 until you notice a drop in current draw.
The pcm looks at the EOT sensor and if it is below 131* activates the GP's then it looks at the Baro and IAT and decides how long to rum them. Sometime you can ccyle the key and reactivate them without AE loosing connection but usually I just DMM them manualy.
As far as testing for key off current draw get a DMM capable of reading amperage and clamp around pass red cable. Should be close to 0.1 as the only thing that should be running is KAM and radio clock. Then start removing fuses 1 by 1 until you notice a drop in current draw.
Last edited by Uzumati; Dec 4, 2006 at 09:25 PM.
Post Fiend
Joined: Feb 2006
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From: Middle Tennessee
You know Alan, as I was reading this post and thinking about the GPR test I posted the other day, I was wondering if the batteries may be pulled down to 10.1 by the GPs.
If I recall, it stated the current being sent to the GPs can read between 8.5 and 12 volts depending on the condition of the batteries. Of course that will only tell you if the GPR is working. Too low a voltage is not going to get it done.
If I recall, it stated the current being sent to the GPs can read between 8.5 and 12 volts depending on the condition of the batteries. Of course that will only tell you if the GPR is working. Too low a voltage is not going to get it done.
Post Fiend
Joined: Jul 2005
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From: 21791
Do you have a digital multimeter? This sounds to me like the AC voltage diode in the rectifier bridge of the alternator is going bad. The rectifier bridge takes the negative half (AC) of the sine wave and rectifies it to DC voltage during alternator operation. When the AC rectifying diode begins to go bad, it will leak AC current back to the batteries, eventually draining them overnight. I did the test on my truck in school and it turned out fine. I don't recall 100% the exact procedure, however tomorrow during school i will ask the teacher and post it up for you. Hang tight.
Post Fiend
Joined: Jun 2006
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From: Central, Al
they can be but good strong batts will stay above 10.5 and thats where ford say to swap em at
EDIT: if the fuse pull test does not cause a drop in current draw then Kris is dead on with the rectifier.
EDIT: if the fuse pull test does not cause a drop in current draw then Kris is dead on with the rectifier.
Last edited by Uzumati; Dec 4, 2006 at 09:57 PM.
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From: Cincy OH
Thanks for the replies! I tested the truck again when I left tonight, and while cranking cold, the volts dropped to 8.6V, and it barelly had enough to turn over. What is odd is that alt. and batteries were new 18 months ago, and they all tested fine last week at ford, I watched!, however, it took the passenger battery 1 hour to charge and pass the load test. It was obviously VERY low. Now it is back to draining batteries.
Also, Alan please elaborate on how to test for a draw. I do have a radio shack digital muiti meter (if thats what it stands for), but not the best w/ electronics! Do i just connect to positive and negative terminals of pass battery and set to amps? There are lots of amp settings, and while fooling at the shop tonight, I managed to blow the internal fuse on my meter, so I did something wrong? Luckly I had a spare. Thanks!
Also, Alan please elaborate on how to test for a draw. I do have a radio shack digital muiti meter (if thats what it stands for), but not the best w/ electronics! Do i just connect to positive and negative terminals of pass battery and set to amps? There are lots of amp settings, and while fooling at the shop tonight, I managed to blow the internal fuse on my meter, so I did something wrong? Luckly I had a spare. Thanks!
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Post Fiend
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From: Central, Al
There should be a "Clamp" or set of jaws on the meter so you can hook it around the positive cable.
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From: Racine Wi
99% of all amp meters are for AC only (some have a small 10 amp DC range), so don't expect to hang a common meter on a battery terminal. I don't think it will hurt them, you just won't get a good reading.
Yellow401, I just had the same thing happen to me on 1 yr old batteries. My voltage at startup was dropping to 8.2 volts. The batteries had a 3 yr 100% replacement, so I took them back and had them replaced. No more problems. I had the exact symptoms as you. Short sit time, no problem. Overnight, nearly wouldn't start. If your batteries are only 18 months old, get em replaced.
Yellow401, I just had the same thing happen to me on 1 yr old batteries. My voltage at startup was dropping to 8.2 volts. The batteries had a 3 yr 100% replacement, so I took them back and had them replaced. No more problems. I had the exact symptoms as you. Short sit time, no problem. Overnight, nearly wouldn't start. If your batteries are only 18 months old, get em replaced.
Logistics Pro
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Here's a thread with some info on battery voltage and starting... check post #6 by MDB:
https://www.ford-trucks.com/forums/5...ow-starts.html
Also, here's a post by Blow_by from TDS:
"Batteries need to be 12.7-8v with no load. When you turn the key they will
drop about 1.5v, so 10.5v's will not start it. You need about 11.3-4v's to
start under load."
https://www.ford-trucks.com/forums/5...ow-starts.html
Also, here's a post by Blow_by from TDS:
"Batteries need to be 12.7-8v with no load. When you turn the key they will
drop about 1.5v, so 10.5v's will not start it. You need about 11.3-4v's to
start under load."
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From: Cincy OH
Thanks for the info! I will test the votage output of the batteries, independently, in the morning when everything is cold. Been driving it all day. Also, I replaced a battery cable that went to my plow selenoid from the positive battery terminal. It seemed to have corrosion all throughout the entire cable, so I am hoping this may have been a source of a draw. I will report back!
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