I have a 2015 nissan versa.  It is cranking but not starting.  I put a new fuel pump in but that didn't help.  Pulled the #3 and #4 spark plugs, changed them, and that didn't help.  I didn't change #1 and #2 since they are under the air intake.  But I did confirm spark on #4 so I am assuming I'm getting sparks on all 4.  There are no error codes coming up.  The only other issue previously was a thermostat replacement and the car was running hot.  But with the new thermostat, new coolant, and Blue Devil coolant sealant addition, the car was running at proper temperature.  After that work, the car ran fine for a couple days and then this starting issue occurred.  I was beginning to wonder about the head gasket, but when I changed the #3 and #4 spark plug I did confirm they had a little gas on them, but no coolant, so hopefully the head gasket is fine.  Should I change #1 and #2 spark plugs? What other things could be causing this issue?