I have a 2008 Kia rondo 2.7 V6. My check engine light came on for spark plugs. I went ahead and changed all 6 and it still came back for a misfire in cylinder 1 and said it was still the spark plug. I swapped ignition coils with a new one to see if it was the problem but now it says the cause is both the ignition coil and the spark plug in cylinder one.
Since you have already replaced the spark plugs and did the ignition coil swap, the list of remaining causes is still rather long. It could be any of the following:
- Faulty fuel injector
- Low fuel pressure
- Vacuum leak
- Faulty camshaft or crankshaft sensor
- Low compression in cylinder 1
- Leaking head gasket near cylinder 1
To diagnose the above requires special equipment and expertise. Depending on your skill level and tool supply you can diagnosis this yourself or take it to a highly rated independent mechanic to diagnosis the cause.