1990 760 started to stall out [ sudden tach drop] after a 30 min drive .it will restart after sitting for 5 min but only run for 1 i can here fuel pump on start up ,replaced crank sensor ,switched suppression relay all grounds are good as are positive leads , with an ignition tester on when running i can tell an instant spark loss ,followed by no spark when trying to restart , now the weird /when it dies i have no spark while cranking but when i release from cranking i will get a spark ,but none on crank it is almost like the old dodges with a ballast resistor when running the car performs to expectation , and is well maintained .after awhile sit for 5 drive for 1.parts are hard to come by where i am so test procedures are welcome ,can a fuel pump relay cause no spark?