I have been chasing random start-up issue that i think may be related to the AFS (Air Fuel Solenoid) on these emission equipped 6.8l machines. 

Machine is
Model: QT10068AVAC
Serial: 3002334146
and runs on LPG that would fault for Overcrank it also had a Check Engine alarm in the history that cleared itself which lead me to performing Problem 40 in manual 0J1195 Rev J. 
After verifying proper gas pressure and verifying the O2 sensor functions properly I checked the resistance of the AFS as described in Test 113 and measured 35 ohms w/ a calibrated Fluke, manual says "approximately 27 ohms".

I witnessed the machine go into overcrank. After resetting the Nexus and attempting another start sequence, out of frustration I hit the on-demand regulator set-up and it fired right up. I had to do this three times a row. I then disconnected the vacuum line that leads from the AFS to the distribution block that connects each side of the regulators and haven't had an issue with start up or Check Engine since.

I wasn't able to call tech support due to the remote location of this machine. The parts diagram for this serial shows the AFS but doesn't list a part number.

My question is, has anyone had any experience with the AFS. I believe it is holding the regulators closed and preventing the engine from getting the proper gas flow to start. 

Thanks in advance.

The AFS and check engine alarm are not latching faults and should clear after a while on there own if the fuel air is correct.  My guess would be the enrichment solenoid/s. There is a connection in those that I have often found loose.  Some of those units have two enrichment solenoids, others only have one and they are fed off the starter circuit so while cranking you should be able to feel a magnetic field with a steel putty knife or something similar (steel and lightweight) on the top of the solenoid.  I think the emissions control is a false flag for your troubles you need to verify that the enrichment solenoid is opening and you have gas flow to the supply hoses regardless of the demand diaphragms.  It is trick to verify the enrichment solenoid are opening and gas is flowing. 
I agree with Peddler. The Air/Fuel Solenoid won't stop the unit from starting. It makes small adjustments when the unit is running and will not latch out the unit. The overcrank problem is more likely where the issue lies.(Problem 18)