I have been having an issue starting my 1997 ranger. It turns over fine with a new battery, but will not fire. In the past, if I let it sit for an hour, it would start right up. A couple other times it wouldn't start for 3 days. I replace the fuel filter, plugs, plug wires and coil. It then started good for 3 weeks. Yesterday morning it was a no start, and again last night. I checked the fuel preassure which was good, but it did not have spark. I disconnected the battery for 10 minutes and reconnected; it fired right up. What could cause this?