put some isopropyl in the tank to eliminate water/ice. switch plugs from cyl. 4 to 5. see if the code changes with every trial. if the code is the same cylinder I would try the injector switch from 4 to 5 . if the code doesn't change then i would strip back the injector wiring all the way to the computer plug. There have been some reports of melted/broken wires in the harness. I don't think it is a valvespring...yet. Next step would be coils and takes a bit more work...........have fun!!