If you have propane going thru into the intake then the pressure relief valves in the injector holder are stuck open,there is two of them I would take off the injector holder and take off the injector And pressure sensor and clean all the passages in the injector holder,when the Vaporizor let's go and let's more pressure into the holder then it can gum up the pressure relief springs with tar from the Vaporizor and cause them to stick open. When you turn the key to just the on position can you hear fuel going into the intake manifold? Sometimes tapping on the sides of the holder with a plastic hammer will free up the reliefs but would be a better idea to clean it good,you can see one of the reliefs when you take out the injector,is a brass colored orifice at the bottom of the injector seat.