I have a 89 Iroc 5.7 it will not start most of the time pump comes on plugs are sparking but it will not start but sometimes it starts up and runs great thought it might be the vats so I have a 68 truck I converted to tpi from a 89 corvette with a chip that eliminates the vats wire I plugged the computer in and the same problem persists the wiring harness looks ok It is not affected by shaking the harness and does not give any codes
any ideals???

If it starts it is not VATS related.VATS shuts down the injectors
You say you have good spark so must be fuel related
Have you checked fuel pressure when it won't start?