Cylinder 4 Misfire P0304 and EPC

[englishmuffin52]

Unitronic Stage 2 2017 Golf R, manual, with 36k miles. At 30k miles had the same code but replaced the coils and plugs. Now i have the same code again but also with EPC. It happened when i put my foot down to overtake someone and went into limp mode. After restart it was fine. I have tried switching plugs and coils and it does not follow them to different cylinders, compression is good, no carbon build up and injectors have been swapped around too still without changing a thing. I have noticed it only happens once I reach 6k rpm. I have tried the 1:1 test by putting my foot the the floor in 4th gear from 1500 rpm upwards and the car runs very smoothly until it reaches 6k. There are no revisions for the tune either, I checked that. I can drive it around normally from day to day still and even put my foot down a bit still without breaking up. Its very frustrating and it feels like it'll soon be a case of just throwing money at it. If anyone knows or has experienced this before, any advice would be greatly appreciated!

 

[Diggs24]

Buy a cheap boroscope off amazon and scope the cylinder. Post vids so we can see what it looks like.

 

[englishmuffin52]

Buy a cheap boroscope off amazon and scope the cylinder. Post vids so we can see what it looks like.

What am I checking with a Boroscope?

 

[Diggs24]

scoring on the cylinder walls
pitting

 

[englishmuffin52]

how can that be corrected?

 

[Diggs24]

You have 1 cylinder acting up. This is a cheap way to see if anything can be seen short of opening the motor. Get one with 8.5mm or less diameter on the camera to ensure it will fit down the hole.

 

[jimlloyd40]

Rebuild. Do a compression check. Are you burning oil?

 

[englishmuffin52]

Checked cylinders, all healthy, compression and leak down came back perfect. No burning oil. Technicians are at a loss so I'm trying a software re-flash next.

 

[jimlloyd40]

Besides the tune what mods do you have?

 

[JerseyDrew77]

OP, are you sure the fuel injector for that cylinder is good?

 

[englishmuffin52]

The guy looking at my car said all injectors are good. May be worth having another look. Other than the tune it's and intake, high flow downpipe and stage 2 clutch (not that the clutch is relavent)

 

[englishmuffin52]

Turns out it was actually the unitronic tune. It just took so long for them to get back to me.

 

[jimlloyd40]

Turns out it was actually the unitronic tune. It just took so long for them to get back to me.

Thanks for the update.