Battery Voltage vs FICM Voltage - Ford Powerstroke Diesel Forum
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Old 01-14-2013, 07:08 AM
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Battery Voltage vs FICM Voltage

Hey guys. I've been doing a lot of reading on FICM issues, and I'm pretty sure I have one, but I'm trying to determine where the exact issue lies.

Symptoms: Starts fine, but runs rough (stutters) until engine gets up to temp. After that, runs great.

I am able to read voltage through the OBDII port (FVP - FICM Vehicle Power, FMP - FICM Main Power) and checked voltages with key on (FVP: 11.5V, FMP : 48ishV), and after cranking (FVP: 11.5V - before alternator kicks in, FMP: 44-48V).

I went with the easiest issue first, battery voltage was low, so I checked it with a voltmeter and it read 12.4V with engine off. I checked connections at the battery, and those are fine. So this is where my question comes in, is this a bad connection or a discrepancy in reading from the OBDII port? Also, is this a good indication there is a loose connection in the FICM (obviously it needs redone, but I'm trying to make sure there aren't other issues so that when I get it redone, I don't hurt the redone FICM). Does FVP read from the FICM and if so, sounds like it's definitely a bad connection in the FICM? Should I be looking for other bad connections?

Thanks for your help!

Last edited by griffgj; 01-14-2013 at 07:23 AM.
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Old 01-14-2013, 07:17 AM
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if your FMP on your FICM is 48V then your set from what i've read.. you could test directly with the multimeter on the FICM itself to ensure your getting a proper reading.. and if your batteries only put out 12.4 volts then maybe you need new batteries! mine usually output somewhere in the 13s
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Old 01-15-2013, 10:38 AM
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FICM should read 48 volts. Batteries with truck off should measure 12.3 volts +
Truck running you should get 13+ volts at the batteries.
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Old 01-15-2013, 11:13 AM
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Guys, thanks for info, but I'm already aware of this. I was just wondering if anyone had any answers to my questions.

Thanks.
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Old 01-15-2013, 11:32 AM
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Not sure if it pulls FVP from FICM. IF your FICM is reading 48 Volts then I would say its ok. I would take a reading directly form the FICM with a volt meter to make sure. Once the truck is started then voltage should be well above 12v since the alternator is running.

You could have some injector issues.
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Old 01-15-2013, 11:38 AM
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Disconnect the batteries from the truck and load test them. The fact that you saw 44volts on the FICM means it's on it's way out. You will see 11.5 volts on the voltmeter for the first couple of minutes the truck is running and it will gradually step up. You should have over 13 volts once the alternator is running.
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Old 01-15-2013, 03:24 PM
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The voltage is dependant on temperature for load. If you select KOEO the voltage will be drawn down by the PCM, fuel pump and primarily the glow-plugs. 11.4v can be fine. When you start, you can expect voltage drops to 10v, again depending on temperature.

Your FICM voltage during this start is relative to the voltage supplied. At 12v+ it should be about 47-48v. At 10v it could easily be 44v and that would be OK. Once your glow-plugs kick off and the alternator kicks in (up to 2 minutes after KOEO), the voltage should be about 14v and the FICM voltage should be stable at 47v+.
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Old 01-16-2013, 06:19 AM
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Here's a question that I probably already know the answer to...Key off (out of the truck) is there supposed to be any voltage going into the FICM? I have a small pull of about .5 drawing with nothing on. Also, anyone ever hear of the FICM being as low as 10v Key On/No Crank and 3v Key On/Crank? I got on here today to just made sure I did it right, because if those numbers are accurate, I believe I'm in the market for a new FICM. (probably some injectors too)
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Old 01-16-2013, 06:24 AM
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Quote:
Originally Posted by twoicebergs View Post
The voltage is dependant on temperature for load. If you select KOEO the voltage will be drawn down by the PCM, fuel pump and primarily the glow-plugs. 11.4v can be fine. When you start, you can expect voltage drops to 10v, again depending on temperature.

Your FICM voltage during this start is relative to the voltage supplied. At 12v+ it should be about 47-48v. At 10v it could easily be 44v and that would be OK. Once your glow-plugs kick off and the alternator kicks in (up to 2 minutes after KOEO), the voltage should be about 14v and the FICM voltage should be stable at 47v+.
I've never seen a voltage drop to 10v when the truck is running even in -20f. The very worst with everything running was 11.2 on the monitor and the FICM is still 47.5 volt.
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Old 01-16-2013, 06:25 AM
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Quote:
Originally Posted by dxusmc View Post
Here's a question that I probably already know the answer to...Key off (out of the truck) is there supposed to be any voltage going into the FICM? I have a small pull of about .5 drawing with nothing on. Also, anyone ever hear of the FICM being as low as 10v Key On/No Crank and 3v Key On/Crank? I got on here today to just made sure I did it right, because if those numbers are accurate, I believe I'm in the market for a new FICM. (probably some injectors too)
If you are 10v key on no crank it's time for batteries and I wouldn't doubt an alternator will be following along shortly after.
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