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Old 02-12-2013, 07:29 AM
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Scan Gauge / voltage question Help!!

I bought a scan gauge to watch the ficm on my early 04 6.0 with a whopping 44k miles on it. I have noticed that when I first start my truck in the morning, the alternator has an output of about 11.2 volts. The ficm output drops to about 45 volts. After about a minute, the voltage comes up to normal, about 14.2. Batteries are about a year old, has a new belt and I had the alternator checked about 6 months ago. If you have a real time gauge, is this normal? If not what is the most likely problem? Voltage regulator? Thanks!!
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Old 02-12-2013, 09:34 AM
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The alternator is normal no issues there... BUT the ficm is getting weak and should be monitored... Voltages lower than 45 volts at the ficm needs to be replaced/repaired.
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Old 02-13-2013, 08:03 AM
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The ficm has low voltage only when I first start the truck, about 30 to 45 seconds, which is about the same amount of time that it takes for the truck to start producing more than 12 volts. Im also watching the input voltage to the ficm which is also low. As an electrician, I know that low volts in means low volts out. I came close to having the ficm rebuilt but hate the down time, even 3 or 4 days. Thats why Im asking if it's normal for these trucks to take about a minute for the voltage to build up. Do you have a digital gauge on yours?
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Old 02-13-2013, 01:22 PM
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The voltage drop is from the glow plugs. they run/cycle for 2 minutes everytime you start the truck, thats why your voltage is low and then jumps up to normal
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Old 02-14-2013, 06:32 AM
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That is correct^^^ The PCM uses the oil temperature to determine the amount of time that the glow plug cycle runs.
The FICM is on it's way out and it will strand you sooner than later, you can get one from Ficmrepair.com were he will just send you a repaired unit with a core charge as soon as you send him your old one one he will refund the core money back to you. He is a good guy with a great rep I have dealt with him myself with great results, highly recommend him.
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Old 02-28-2013, 05:20 PM
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The regulator in the alternator is intentionally timed to not start charging until after the glow plug cycle because the load of the glow plugs would toast the alternator. I researched this when I installed my ScanGauge II and noticed the low voltage right after starting.

I had my ficm repaired at ficmrepair.com about two years ago and it has been within .5v of 48.5 ever since. Highly recommended. I shipped mine to them the day after Christmas and got mine back and installed before New Years day! Of course, a lot was paid for overnight shipping both ways.
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Old 02-28-2013, 06:19 PM
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Quote:
Originally Posted by Aerospace_ITGuy View Post
The regulator in the alternator is intentionally timed to not start charging until after the glow plug cycle because the load of the glow plugs would toast the alternator.
I have seen people make that statement before, but it simply is not true. Put a clamp-on ammeter on the alternator and crank her up. It puts out 80 amps (if a stock alternator) right from the get go. The reason for the low voltage is the glowplugs are pulling 150 amps and drawing the voltage down even with the alternator trying to keep up.

MikeB
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