This issue was found and solved on my RV.
The genset would crank and run flawlessly, for a random period of time. Perhaps between 2 hrs, sitting in the drive way and 30 minutes on the road. I did run it in the driveway for 4 hours once, and thought the issue was solved, but no.
The generator would stumble, and then finally quit. Clearly a fuel supply issue. I replaced filter and pump. No improvement.
This is NOT the ten second shut down due to temp/oil pressure switches.
Then I noticed a VERY strong vacuum in the gas tank. Well beyond simply removing fuel and creating vacuum. Accompanied by a huge "inhale" when removing the gas cap.
Very surprised there was no CEL for this condition.
I began researching the EVAP system. There are supposedly TWO Solenoiods to operate the EVAP system:
-Purge Solenoid, near the intake manifold, to supply intake vacuum
-Vent Solenoid, to vent the EVAP canister.
The Purge Solenoid appears to be functioning correctly. At least it was not stuck open. I cranked the engine and verified there is not constant vacuum. I assume it's OK.
I say "supposedly two solenoids", because I never found the vent solenoid. Even after I purchased the part at autozone to help me find it. Still, I never found that part. I'm not convinced that Ford did not have an alternate way to vent the canister. I'm still researching this issue. It should be near, or in the canister, but I never found it.
BUT, in the end, I did find some insect nesting in the 3/4" x 36" corrogated plastic air hose that vents from the tail end of the EVAP canister. 100% blockage.
This solved my issue.
There has been some discussion on the board that vacuum in the main tank can starve the little, low psi fuel pump for the genset. I can verify this was what was happening. I would leave my gas cap loose, just sitting in the fill nozzle, and run my genset for 400 miles, no issue. I had someone else pump the gas and about 30 minutes down the road the genset stumbled and quit. When I got out, I knew what I was looking for and sure enough, I could hear the genset fuel pump pumping like crazy, but not moving fuel. I loosened the gas cap, witnessed the tank inhale, cranked the genset and we were on our way again.
But this is a VERY strong vacuum, as mentioned above. If you don't notice the big "inhale" when removing the cap, you probably have other issues. I'm not sure that burning fuel while traveling will create this kind of vacuum.
Anyway, this is an intermittent, hard to reproduce issue that is very frustrating. I hope this helps some one.
BTW, the corrogated plastic air hose just slips on and off, no clips or clamps. You can slide it off w/o tools and hose it out to check it.
I put some aluminum screen on the end of mine, with a couple a zip ties.
Then I took the $100+ purge solenoid back to Autozone.
