car wont start after gas is pumped

My 1993 nissan pickup truck won't spark or start help

Could it possibly be the gas cap? I've heard sometimes if the cap is loose there will be starting issues...

The vapor canister purge valve may be stuck in the open position. This causes vapors of the gas you are pumping to go directly into the engine. Too much fuel vapor in the engine causes an over rich or flooded condition and can result in a delayed start or no start. Is the check engine light illuminated?

after you get gas and it won't start do you smell gas from cranking it over ?

Check for any OBD trouble codes, you may have one or more set related to the EVAP system. A bad purge or vent solenoid can cause problems with gas tank pressure. Most auto parts stores will do a free check for trouble codes if you can get your car up to one. You can also pop your gas cap and see if it feels like there was excess pressure in tank.