When My 1995 Explorer xltis in traffic or at a standstill it shuts off but turns on with no problem. once it shuts off the all the dash lights go on including the check engine. Now before it turns of it starts to rumble and starts spitting black smoke out of the exhaust also starts to smell like gas. it has a new fuel line and fuel pump. relays are new. ive even taken it to a ford mechanic but noerrorsshow up on the computer. anybody have any idea what could be wrong! PLEASE HELP!!!!!!!!!