The 6.0 Powerstroke Fuel Injection Control Module (FICM) is a high-voltage driver for the fuel injectors controlled by the vehicles Electronic Control Module (ECM). Think of the ECM as a low voltage (~5vDC) processor that looks at all the engine and cab sensors (Accelerator Pedal Position, MAP sensor, Cam sensor, ICP sensor, etc) and then calculates and commands a volume of fuel from each injector. The HEUI (Hydraulically Actuated Electronic Unit Injection) fuel injector operates like a syringe, using the engine's high-pressure oil to push down on a plunger inside the injector body to push fuel out of the injector nozzle. By design and operating with ~5v the vehicle ECM is not electronically strong enough to directly control the fuel injectors, so the ECM commands the FICM to do the work at the injectors.
The top component of each fuel injector contains a spool valve that is comprised of 2 coils (electromagnets) with a rod positioned in between these coils. Think of each injector as having an ‘on coil’ and an ‘off coil’, or ‘open’ and ‘closed’ coil. During normal injector operation, the FICM sends a ~0.6millisecond duration ~48v (DC voltage) to the ‘on coil’ which creates a magnetic field and draws the spool (metal rod) to the open position, allowing high pressure oil to push down on the injectors’ internal plunger. To stop the flow of oil and fuel (stop the plunger from continuing its downward stroke) the FICM sends a second 0.6millisecond duration ~48v to the ‘off coil’, which pulls the rod/spool back to its closed position.
The time in between these 2 signals is the injector on time, or Injector Pulse Width (IPW). The IPW on the 6.0L ranges from less than 1ms up to about 2.2ms depending on how much fuel the ECM is requesting. Having no internal, mechanical spring to hold open (or hold closed), the spool valve; the actuation of the fuel injector relies on the FICM voltage (and the magnetic field) to properly pull the spool valve into either its open or closed position.
A common failure with the 6.0L FICM is ‘low voltage’ caused by various internal circuit board components aging, wearing, and deteriorating, which prevents the FICM from outputting the proper ~48v to the injector coils. It is often worse when ambient/outside temperatures are below 40-50deg, as you can imagine. If the FICM is only outputting 40vDC or less, the spool valve may be slow to move to the correct position which would mechanically delay or retard the SOI (start of injection) causing very hard or no starts.
The spool valve inside the injector can mechanically wear over time which can cause identical symptoms as a low voltage FICM. When the spool wears, it becomes loose inside the injector body and can get cocked sideways and ‘drag’ inside the spool’s bore and can become slow to move to the correct open or closed position. Further worsened by cold, thick engine oil trying to pass through this valve. So, if you have a 6.0 engine that is hard to start when cold, from a diagnostics standpoint it is best to simply check that you have ~48v FICM voltage while cranking/running. Repair or replace your failed or faulty FICM with a wide selection of FICM's and repair parts at XDP.