Just bought a 1991 mustang gt with auto trans. Picked the car up knowing it had a misfire but tried to make it home with it after buying it. Got about 20mins into driving and the misfire got worse. Then the car just shut off and got alittle hot (250°). Got it towed home and checked everything. Cylinder 5 spark plug boot was touching the header. So figured it shorted out the coil so I replaced with a spare. Then checked spark, fuel pressure and timing. All are good. The car will not fire even on starting fluid. What should I check next?