if you are getting P0204 then its just what it says. you have a bad circuit. which means you could have a short in the wiring, or a bad injector or a bad connection. check all the wires leading to the #4 injector. and if the injector isnt firing like its supposed to P0304 will show up because #4 will be misfiring because of no fuel so it trips that code. they are both linked. so check the wires and connection and if they look fine then its the injector. like the DTC says. thats what they're there for. good luck!