how does one check the ficm voltage?
What you need to do is go to a Auto Zone store and purchace a ScangaugeII monitor gauge, it is a on the shelf item and will cost you $160.00. There is a function on it called X-Gauges from there you can program in PID #s for the sensors for the 6.0 PowerStroke engine. This tool will read virtually everything the PCM (trucks computer) sees, you can read the ficm voltages and sync EBP.EGR,MAF,MAP ond on and on, again everything.
Once you get the scangauge we can help you diagnose what your truck is doing, without it all we can do is guess and you can start throwing parts at it but you know how costly that can be!
Yoou can leave the ScangaugeII plugged into the OBDII port all the time and it will read the engine data temp oil cooler temp, injector pressure, hpop duty%,ficm voltage, and right on down the line, the only things it can't see is: fuel pressure and exhaust temps but everything else it will see.
A lot of us use it myself included and it's probably the best money I have spent on my truck, oh yea it also is a code reader.
There are more expensive units out there and many fancy units available but for the money it can't be beat.