I am trying to resurrect my fathers 92 Dakota with 3.9 engine. I pulled the plugs, shot in some PB Blaster and turned it over. Put the plugs back in, dribbled some fresh gas into the throttle body and to my amazement, fired right up. The fuel tank appears to be empty ( I tried to pump it out but appears to be empty). Can I unscrew this cap and using the electric fuel pump, purge the lines of any old gas? I don;t want to get any crap into the injectors.