Superduty starting issues
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1st Gear
Joined: Sep 2012
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Superduty starting issues
2015 F250 6.7L here. When starting it seems as if batteries are weak and really bogs to start vs the usual quick start up. I replaced both batteries and still the same. Checked battery voltage not running and they’re at 28.4v. Checked while running and they’re at 29.9v. Checked both times, at idle, with all components off. Possible alternator? Starter? Relay somewhere? Any help is appreciated before I just start buying new parts. Thanks in advance.
Laughing Gas
Joined: Oct 2007
Posts: 946
Likes: 99
I know nothing about diesels, but do k ow a bit about electrical .
there is 2 batteries i know , and as far as I know , they are wired parallel, as positive to positive, negative to negative, which is giving you 12 volts .
If they are in series , positive to negative , that will make you 24 volts .
Regardless, with only 1 volt change from running , seems off .
there is 2 batteries i know , and as far as I know , they are wired parallel, as positive to positive, negative to negative, which is giving you 12 volts .
If they are in series , positive to negative , that will make you 24 volts .
Regardless, with only 1 volt change from running , seems off .
FTE Legend
Joined: Mar 2017
Posts: 31,800
Likes: 9,127
From: Western NY
Those voltages are very troubling...
Here's a link to a search for "6.7 Powerstroke alternator voltage regulator symptoms"
https://www.bing.com/search?q=6.7%20...FEAB285CB09C03
I have to imagine it won't start or hard to because the system is protecting itself from excessive voltage.
Im not sure but maybe pull the alternator and have it tested somewhere. Not saying thats the problem but that might be a good place to start.
That link should provide a place to start. Is the truck a new to you or did this just start?
You're at double of what the truck runs with of 14 volts. That's crazy.
Here's a link to a search for "6.7 Powerstroke alternator voltage regulator symptoms"
https://www.bing.com/search?q=6.7%20...FEAB285CB09C03
I have to imagine it won't start or hard to because the system is protecting itself from excessive voltage.
Im not sure but maybe pull the alternator and have it tested somewhere. Not saying thats the problem but that might be a good place to start.
That link should provide a place to start. Is the truck a new to you or did this just start?
You're at double of what the truck runs with of 14 volts. That's crazy.
FTE Legend
Joined: Mar 2017
Posts: 31,800
Likes: 9,127
From: Western NY
Here's a good post with info. Brings up the battery sensing circuit which is a single bare wire running under the engine on the engine girdle which is known to be a problem.
https://www.thedieselstop.com/thread...issues.613897/
https://www.thedieselstop.com/thread...issues.613897/
Mountain Pass
Joined: Apr 2024
Posts: 221
Likes: 84
As others have mentioned, its a 12 volt system. So you should be measuring 12 volts resting and 13.5 volts running. If not, get those batteries disconnected now! It could damage the modules, and PCM. Did someone re-wire the batteries into series? Or could these be 24v batteries (which I doubt)?
Backing up, and don't take offense, but you are measuring the voltage across the two terminal of the same battery right?
Backing up, and don't take offense, but you are measuring the voltage across the two terminal of the same battery right?
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wickedmax13
1987 - 1996 F150 & Larger F-Series Trucks
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Jul 20, 2010 04:27 PM
