Hi I have a 03 Nissan 350z i just did an engine swap on it and once we finished it backfires and we had a DTC code that read misfire on cylinder 4 so I replace the coil and put a new plug in and it still read the same DTC code. So the next thing we did was swap the fuel rail (with injectors) from the old engine to the new one. Still the same DTC code was read and it still has the backfire. Don't know what to do next could use any help thanks.

 

Make sure the correct plug is connected to the correct coil pack.

 

+1^. my engine had dtc p0300 too and I thought the coil plugs were wrong on 4 and 6 so I switched the plugs and it started doing the backfire. try to change them and rest ecu.