if you follow the fuel line from the tank into the engine compartment the fuel line will first come into the lockoff solenoid,this has a small filter in it,take out four small bolts and canister with it in it should come right off,watch as there is a o-ring and seal here. the fuel line then comes from the soleniod up to the vaporizor. there is a 17mm hex on the top, this might be the pressure test fuel plug you mentioned,if you put a guage there you should have approximately 4.5 PSI while running and under load also