Ford Focus - Fault Code P0304

[Rick]

The car (1.6 ZETEC SE, two camshafts) with check engine light came on. The fault - misfire on cylinder 4. The owner replaced spark plugs before. Right after the replacement the car was running good, but later starts hesitating on sudden acceleration. According to the piezo transducer’s waveform can be seen the difference in working exhaust valves. At idle the breakdown voltage in cylinder 4 is higher than in the others. During snap throttle it has strange firing line. I replaced spark plugs in cylinders 3 and 4, but no changes. High-voltage wires are good. I don’t have any high-voltage wires and coil to replace.
What can it be – valves or high-voltage part?

[Kelvin]

Are you having a problems when the starter does crank the engine?

[Rick]

I didn't record while cranking. The car starts and idles fine. Tomorrow will replace high voltage wires and a coil.
Attach throttling waveform.

[knyshmotors]

on your waveform clearly shows failures in the secondary circuits of ignition cylinders 1 and 4. The overvoltage combustion and reduce the burning time characteristic of the fault ignition wire or spark plug gap large. since the cylinder 4 is more pronounced the problem, I can assume the fault ignition wire ... although there may be other reasons, but should look at the 4-cylinder.

[Rick]

Thanks for the reply. I replaced the ignition coil with a new one. Everything is fine.
No ignition problems to date.