I dont know what to say other than maybe an intermittent broken wire causing the problem somewhere in the ignition components or maybe a fuel pump issue. i had a problem with the wires on the inside connector on my fuel pump corrode because the insulation around the wire was eaten away and the wire started to corrode and come out of the connector, i redid the wiring and all has been fine, i would say go to all your components as far as fuel pump and ignition starting with the easiest and tug on the wires slightly at the connectors and see if any fall apart, old wiring tends to do this time to time. I had an injector wire do it to me once on my car and once on a friends b13. just an idea. old wiring mixed with vibration and heat doesnt go well after a while.