Chevrolet Repair: Ignition coil, s10 blazer, v6 vortec

Question
I have a 93 S10 blazer with a V6 vortec engine, It runs well. Yesterday, It would crank but not start. I found that I had no spark from the coil. I replaced the coil and it start and ran just fine; for about 3 hours. Then it did the same thing. What would cause the coil to stop working?
Also, this vehicle has an electronic transfer case. When the switch is pushed you can hear the "solinoid" kick in but the transfer case doesn't engage. How do I find out what's wrong and fix it.
 Thank you

Answer
Hi Tom, I would replace the ignition module for the no start problem. As for the 4x4, the most common thing is the encoder motor. It could be other things too but this is the common part to go bad. Try disconnecting the the battery and the try the 4x4 after that. Sometimes this will get the system going.

Mark