1988 Corsica

I have a 1988 Corsica with a 2.0litre 4 cyclinder. On my way home it made a kind of pop noise and lost a lot of power. It made it home but was running very rough and I could smell unburned gasoline. When I checked the sparkplugs I had spark at 1 and 4 but none at 2 and 3. I replaced the plug wires but I still do not have fire at 2 and 3. What else could this be. The car has 80,000 miles on it and this is the first problem I've had with it.