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Discussion Starter #1
My 6.0 is having problems staying running because of low voltage.

I got the code saying it was either the battery or the alternator that was bad, so I pulled both batteries and the alternator and had them tested. They all passed. I had some corrosion on the battery terminals so I scraped them clean and put it all back together. It ran good for about 20 minutes. Then I watched my battery voltage gauge go from 11 to 10 to 9 to down to 7-6 and then the truck died.

Sometimes it will still cycle and start, but die shortly after, and other times it will just crank and crank. I was also getting these codes the last time:
P0046
P0560
P0562
P1378
But I think their all low voltage codes related to whatever my problem is? Any help?
 

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Discussion Starter #2
I should also say I have a set of interstate batteries on there now. They production date on them is March 2019
 

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Did you pull the battery and alternator to have them tested? I like this better than the in vehicle test. Either one, at the parts store, the testers are not really rated for a double battery diesel. An alternator can be intermittent and test well in the store, but fail once in a while on the truck.

If you trace the negative battery cables back to the frame, and check the ground you may see corrosion and clean that. When its running, I like to take voltage across the battery terminals, and then go across various ground like the black cable, the engine, the alternator case. The voltages should be nearly identical. If there’s a difference, then you you found a bad ground. Could even be corrosion where the alternator attaches to the intake manifold.

Also, do a visual inspection of the wiring to include where the loom goes by the radiator.

IME, when I see corrosion on the terminals from acid, it tells me I have no more than 6 months left on the battery. In my RV, I ruined two sets of batteries by leaving them in and draining them. One they’re drained, you can’t really recharge them. My first two interstate batteries in my RV only lasted a year. They just can’t take being drained down to three volts.
 

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Discussion Starter #4
Yeah, I pulled the batteries and the alternator to have them tested. I will keep check wires.

I hooked my charger up to the driver's side battery and it charged the passenger side too.

Thanks
 

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Are there any accessories installed that could be draining power overnight?
 

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Done any engine work recently?
 

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Did the cluster battery light turn on and stay on when running?

The continuing voltage drop while running speaks to no alternator output. Connector to alternator, alternator itself, fuse links between alternator and battery, or the connection is not attached.

The dropping of voltage below 9.2 volts is problematic to the FICM, it usually stresses them to the point of circuit destruction.
 

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Discussion Starter #9
If I don't have a good connection down to the starter, would that cause this problem? Basically, is the starter part of a circuit on these trucks?

That seems to be the only connection left I haven't traced and cleaned.
 

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Discussion Starter #10
The battery light comes on when I'm waiting for the glow plugs to warm up, but it doesn't come on again
 

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I’m voting, well guessing, alternators and batteries.

The starter should not cause your voltage to drop.

As mentioned a couple times earlier, a bad battery or bad alternator can test good in the store. It’s a combination of the problem being intermittent and the store’s equipment not being strong enough.
 

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Discussion Starter #12
Just picked up a new alternator, we'll see what happens.

My batteries are holding a charge. They stay around 12 volts over night or over a couple days if I don't run the truck.
 

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12.0 is too low. 12.6 is much better. Good luck with the alternator
 

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Discussion Starter #15
The batteries actually read around 12.4v. If I take a reading from the alternator it reads 14.xx volts. It's the same with the new alternator. I'm still losing power. How do you test the fuse able link?
 

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So the batteries are at 50% to 75% charge.

Where exactly do you have the leads attached to when saying it reads 14+ volts? Connect your negative lead to a battery negative terminal. Without the motor running, what does the alternator post read? Can you post some pictures on the terminal on the batteries?
 

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Discussion Starter #17
Okay, so I wired from the back of my alternator to the positive of my passenger battery. They were reading about the same voltage 14.xx but my gauge still showed me losing power 11 down to 10 which is what the drivers side was reading.

I turned the truck off and checked the volts on both batteries. They were both 10.56 or really close, which makes me think they're still wired together?
 

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Discussion Starter #18
So the batteries are at 50% to 75% charge.

Where exactly do you have the leads attached to when saying it reads 14+ volts? Connect your negative lead to a battery negative terminal. Without the motor running, what does the alternator post read? Can you post some pictures on the terminal on the batteries?
I put the positive on my voltmeter to the back of the alternator, where the red wire is connected. Then the negative on the negative post of the passenger battery when I get the reading of 14 volts. This was right after I pulled my battery charger off. It said they were 100% charged.
 

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Discussion Starter #19
With the truck not running I just got a reading of 12.89 with the voltmeter on the negative of the passenger battery and the red wire on the back of the alternator. Which is the exact same reading I get when I put the voltmeter on both terminals of the passenger side battery
 

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So that tells me the wiring is good. Keep in mind, a multimeter and resistance drops are not the best way to test these wires, but the best way I can. You could have some fraying in the cables somewhere that is not effecting the multimeter, but would a page current. I don’t mean to send you down a rabbit hole with this checking grounds.

I really don’t understand why you’re getting all these different readings on the batteries with them off. 12.4 to 12.9 is a big difference. My guess is still a battery alternator combo.
 
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