No spark 86 cammaro

I have an 86 camaro with a 2.8 L v-6(fuel inj)
Here's the problem At times I go to start the car and it has no spark. When I check for voltage at the coil, resistance through the pick up ect. Everthing check out to normal tollerances. I put the dist cap back in place and the car fires up. It will work fine for a few days then it won't start again. I've check for loose conections, replaced dist control module(3) times, replaced coil and the dist pick-up. Again after replacing these parts the car will work fine for awhile then it reverts to the no start condition. There have been times when it wouldn't start I'd leave it and go back a short time later and it starts right up. Any ideas what could be causing this? I've run out of ideas.