1990 ford 4.9 clubwagon engine problem.?

[isabel l]

I have in my shop a1990 clubwagon ford with 4.9 inline 6 engine.The van no start because have no spark at the plugs.We change the sensor inside the distributor and the module too, now it start and idles fine but when you hit the gas hard the engine dies.The fuel pressure is about 50-58 psi all the time , I check the injector pulse at trouble time and it seems like the pulse is fail, when relase the pedal it is back. Please if you are ford expert or know about any common cause of this problem ,help me .I,m lost and expense a lot of time on this van.