I am inclined to agree with Bowhunter. If both the fuel and the fire are not occurring at the same time after having been working shortly before, then it would seem that the safety portion of the system is interupting the sequence. Check the pump relay, fuel pump oil pressure switch and especially the wires and connectors. the grey wire coming from the pump goes to both the relay and the switch, so when it is running those two will be hot. check them once it dies. process of elimination, good luck.
Rich