Hi Everyone, I'm trying to figure out if I have an electrical issue. When I hooked up a volt meter to my battery this morning, It read 12.20 volts. I turned the key to let the glow plugs turn on and the voltage dropped to about 11.20, once the key is turned to start the truck, the voltage drops below 10 volts. Also, while driving, I read my scangauge II voltage and every couple of seconds the voltage changes, and ranges from 13.7, to 14.8. This seems like a huge change considering this is highway driving (steady rpm, etc).

Now, here are some answers to questions you may be asking:
-Recently replaced the alternator with a DC Power 180amp
-Recently replaced both batteries with Duralast Gold
-With the test above the truck started really quick (mostly concerned that voltage dropped to under 10volts and dont want to damage anything).
-The reason I'm asking, is I know that if the ficm drops below a certain voltage, it can be damaged. I also know that in the 7.3 diesels, the truck will not even start if voltage goes below 10.5. I recently replaced the alternator becuase I had issues where the truck wouldnt start at all, and according to autozone i had a failed voltage regulator so I replaced the alternator. Had an issue with truck starting again a week or two later, so I took the truck to autozone and they said it still had a failed voltage regulator. I figured the alternator was good, and so I decided to replace the batteries. So is it ok that my voltage drops below 10 volts when cranking the engine? I'm afraid that something is not right and I dont want to mess up my ficm.

Thanks in advance

 

If the battery is cold it might be a little low. How long did it set since the last time you drove it? I keep mine on a float charger because I drive it on the weekends...

 

Yes it was cold, around 30 deg f. It had been a couple of days since I started it last.

 

Good batteries at rest overnight should be at least 12.5 volts. Ideal is 12.7 volts. When I crank the engine the batteries drop to app. 11.5 while cranking and then goes above 12 once the gp's time out. If you don't have a current draw when the truck is turned off it sounds like you have a weak bettery or two.

 

I'd say there is something going on, needs more monitoring. First off, I don't like the Scangauge for monitoring voltage. I have a dedicated voltmeter in my truck, and the Scangauge doesn't read even close to the voltmeter half the time. 12.2 volts is 50% discharged on a normal wet cell battery, so 12.2 volts is way too low just resting. Should be at least 12.5, if not 12.6. 12.65 is 100% charged. So one thing to figure out is why that is happening - not driving it enough, takes 4 hours to properly charge the battery, very cold out, etc. Everything else you mention could easily stem from just a poor state of charge on the new batteries. I would start by doing a full 24 hour charge with a 10 amp 3 stage computerized charger, get both batteries fully up to to charge and take it from there.

Brian

 

Your voltage is too low when cranking. It could be the batteries, and it could be a wiring issue, like a bad ground, or it could be a dragging starter.

 

Sorta Highjacking ---
I know MC5C mention that the SGII may not be as reliable for monitoring voltage, BUT I am still curios about the symptoms of the fluctuation value while running at HWY speeds, could this be systematic of something else? or just the error allowed in SGII reporting. I have same issue I am concerned about, except in my case its all the time.

 

Ive got the exact same thing going on. Sure hope you find something because i cant. All connections are good. Batts checked good for soc and cca tests, seems to be charging fine , etc. had ficm gone through a year ago. Saw volts down to 43. Had it gone through again and see the same volts on it.

 

I had same issue replaced power supply board on Ficm. I bought mine from international for $188! Works fine now and is 48v all the time.

 

I can't find a good chart online, but a battery is 12.6 volts at 70 degrees and about 12.4 volts at 32 degrees.

And the standing voltage goes lower the colder it gets.

Josh

 

IIRC the 6.0L Cutoff is 9.6Volts when PCM Resets

You may have a Dirty Connection or a Battery with Bad Cell

Hydrotest Each Battery Cell

Clean All Charging system Cables even Follow Grounds to where they Mount at Frame and Engine Clean them and Smear Vasiline or grease on connections

Also KEEP IN MIND that the Battery Voltage Taken at the OBDII Port will be 0.2-0.4volt LESS then when Taken Right at the Battery
So things Might NOT Be as Bad as they Look Take Voltage at Battery Terminals

 

You may want to do a voltage drop test on the cables.
The thing is a cable can LOOK GOOD and still
be bad inside and you will not know till you do a voltage
drop test. This guy does a good job on how to do this test.
I guess that comes from teaching the class.

Sean

 

Thanks Sean, Benny and Josh. Ill test the cables this week, I was all ready planning on replacing the batteries at the end of the month, no reason other then Preventative maintenance. My truck makes me money so I better take care of it. Every week for the last few months I have been replacing a hose a gasket , a grommet ect.. Just to be on the safe side.

 

As Bullit390 stated, voltage will drop with temperature. You can also have easily a */-0.2vdc variation with a voltmeter. The Scangauge is not a reliable source to go hardball on battery voltage. Even the plug-in power port models will show variations based on what port they are in.

I've seen some =/- 0.4 voltage swings on several trucks, all with good electrical systems.

Here is a chart showing some starting voltages from a few years ago on another forum.

 

Thanks to everyone for your replies.

Today I spent most of the day driving around, including 2-30 minute drives on the interstate. I looked at my last two sessions and the scangauge reported about 12.5v before I turned the key. Once the key was turned it again dropped about a volt, then when I cranked the engine over the voltage dropped to about 10.7, instead of the sub 10 that it had before. I think the new batteries may have just needed to get that good charge. Tomorrow morning I will use my volt meter and measure directly from a battery and see the results. I also just realized that I installed a ham radio about a month ago, but I dont think that should be drawing any power when its turned off. If I still keep seeing the same issue after a few days, I will disconnect the radio and check results.If still no go I will check the battery cables themselves. Thanks again everyone, I'll let you know how it goes