If it has a swing out style tank rack then the adjustment of the micro switch on the gate latch should be confirmed. Make sure the switch wiring is ok and wired correctly. If this checks out ok then you will need to check to see if unit has a low fuel pressure switch that s located on left side behind the coolant reservoir. This switch could be going south and needs replaced. If the fuel pressure switch is good along with the wiring, then by all means make sure your refillable tank is delivering liquid lpg instead of vapor.