Chevrolet Repair: 1979 starting problem, distributor shaft, vacuum advance

Question
I have 1 1979 small block 350. I have an intermitent starting problem. Engine will crank strong ,all brand new- starter,battery, ignition module, cap, rotor. Will start 20xs, hot and cold, wet and dry, then out of the blue, won't start. Cranks strong but will not fire as getting no spark. Try it 3 days in a row - zero.  Fourth day turn the key and it fires right up????

Answer
HI AUGIE,BEING THAT THIS IS A NO SPARK PROBLEM THIS SOUNDS LIKE A PICK UP COIL PROBLEM..[POLE PIECE] THIS SITS AROUND THE UPPER SIDE OF THE DISTRIBUTOR SHAFT NEXT TO THE MODULE THAT YOU REPLACED. THE DIST WILL HAVE TO COME OUT OF THE ENG,PULL THE ROLL PIN AT THE BOTTOM OF THE DIST SHAFT BY THE CAM DRIVE GEAR AND REMOVE THE SHAFT FROM THE DIST CASE. ONCE REMOVED THERE IS A VERY SMALL C-CLIP THAT HOLDS THE PICK UP COIL IN PLACE,REMOVE THE CLIP AND LIFT UP ON THE PICK UP COIL TO REMOVE. REPLACE IN REVERSE ORDER. USUALLY THE PICK UP COIL SHORTS OUT WHEN THE VACUUM ADVANCE WORKS AND THIS PULLS THE WIRES AND SHORTS THEM OUT..LOOK VERY CAREFULLY AT THE 2 WIRES GOING TO THE PICK UP COIL AND SEE IF ONE OF THE WIRES IS BROKEN [ALMOST IN HALF BUT NOT ALL THE WAY] OR CUT...I HOPE THIS HELPS YOU,,,TOM...