2002 Ford Focus 2.0L DOHC with engine code P0304, what should I check next?

Question

2002 Ford Focus 2.0L DOHC with engine code P0304, plug check good, wire checks good, no vac. leaks. What should I check next?

Answer 1

I would check for intake leaks first, then the fuel injectors (if you use cheap low octane fuel that might be causing the issue) you can try to fill up 91 octane from shell and use a good fuel injector system cleaner and see if that fixes the issue you have.

Possible causes:

- Faulty spark plug 
- Clogged or faulty fuel injector 
- Faulty ignition coil 
- Fuel injector harness is open or shorted
- Fuel injector circuit poor electrical connection
- Ignition coil harness is open or shorted
- Ignition coil circuit poor electrical connection
- Insufficient cylinder compression
- Incorrect fuel pressure
- Intake air leak

Answer 2

P0304 Ford Code - Cylinder 4 Misfire Detected
Read more: https://www.autocodes.com/p0304_ford.html