The odds of an EMF generating a spark, even with it being an EMP powerful enough to knock out a radio, are so insignificant it's more likely the car get struck by lightning. Also, gas tanks don't tend to explode unless they're basically empty and full of pressurized fumes. You're dealing with magnetic waves, something would need to convert them back into electricity. If anything sparks, it would be electronic rather than electrical and to get sparks, it would need to be insanely powerful.
An EMP of enough power to fry a stereo is also likely to just fry the car's computer as well and bring the vehicle to a halt. In fact, I'm about positive my car has been shot by them by the a*hole road crew guys.
A half dozen times over the years, I've seen the road crew guys trying to keep out of sight and point a weird little gun at me that was clearly home made. It wasn't some Sharper Image radar gun that's for certain.
Each time it happened, soon after I started having all sorts of computer nightmares and sensors repeatedly dying.
I'm certain it was a small microwave cannon, EMP or ion cannon.
Why they did it and continue to do it, I have no idea but I saw one again just this year.
