Massive voltage drop when key is turned on - Ford Powerstroke Diesel Forum
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post #1 of 11 Old 09-23-2012, 01:59 PM Thread Starter
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Massive voltage drop when key is turned on

First off my truck is a 2000 7.3 Auto 4x4 with a Gearhead chip. I also have an exhaust and intake. So i have had this problem and have been dealing with it for about 2 months and it has just gotten progressively worse. Now when I turn my key on the batt. gauge in the dash jumps to 12v within a 1/4 on a sec. it drops to around 10.5v after about a min. and a half it jumps back up. I then try to start and batteries are dead all that happens is a relay clicks. batteries have been load tested good and all new terminals (solder and copper crimp on done by napa). I have checked ground wires and I used a voltmeter to confirm grounds are good.

2000 7.3 4x4 ranch hand everywhere, 18000 lbs warn winch, pisa lights, 5 inch turbo back, ts 6 pos custom tunes by Gearhead Automotive, 6637 diy 07, harley lights
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post #2 of 11 Old 09-23-2012, 03:29 PM
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That drop sounds normal to me....

You have to remember the Glow Plugs can draw almost 200A and, after a min, you've consumed a Lot of current.

How were the batteries Load Tested? You need them to be fully charged-up and tested, individually, at a High Rate. The Auto Parts Stores all use these "dinky" 100A testers and we have Really large capacity batteries (for good reason with that GP draw) and those are for 6cly "ricers" who don't

You need like a 300A Load to properly test these batteries. Try to get them properly tested first, then maybe consider the Starter could be the issue maybe (if all the connections are good)
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post #3 of 11 Old 09-23-2012, 03:32 PM
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Sounds like GPs kicking on
I'd check the GPR for proper operation



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post #4 of 11 Old 09-23-2012, 03:43 PM
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Quote:
Originally Posted by jesilvas View Post
Sounds like GPs kicking on
I'd check the GPR for proper operation
By his post it is operating,
I'd guess it has to do with bad connections, and or a bad set of batts,


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post #5 of 11 Old 09-23-2012, 04:04 PM
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Operating correctly? Maybe kicking on late, kicking on and off?



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post #6 of 11 Old 09-23-2012, 04:51 PM Thread Starter
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I actually used a load tester big enough to handle d4 batteries couple weeks ago but I have worn out 2 sets of batteries in 4 months I'm on my 3rd. My passenger battery terminal melted around the post which is why I redid my terminals. When i pried that crap off I could smell sulfur so I had napa test it and they said it was good but I am just burning through batteries and having to jump my truck off to get to work or get home from work.
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2000 7.3 4x4 ranch hand everywhere, 18000 lbs warn winch, pisa lights, 5 inch turbo back, ts 6 pos custom tunes by Gearhead Automotive, 6637 diy 07, harley lights
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post #7 of 11 Old 09-27-2012, 01:06 PM
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Are you over charging


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post #8 of 11 Old 12-09-2014, 07:26 PM
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Ever figure out the issue?
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post #9 of 11 Old 12-09-2014, 07:44 PM
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My random late-to-the-party guess would be a bad starter. Like wore out bearings. The starter moves, but requires more current to do so... A repeated killing load on batteries will kill them.

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post #10 of 11 Old 12-09-2014, 08:18 PM
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I'm having this same issue... It's like something is draining my batteries. At full charge it starts up. Drive it around, all good. Park it and 30 min later, turn the key on, volts go up to 12v, 1/4 sec later drops all volts, and no start. I have to plug in my trickle charger over night and we start it all over again... Gps works but within the 2 minutes of run time it will drop from 12.5v down to 9.5v. Once I start the truck it jumps up to 12.5v at the alternator and won't charge to 14v at all. Even after got shuts off. Any advice? Thanks.
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