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Misfiring above 5k rpm...

duong1994

Passed Driver's Ed
Location
Phoenix, Arizona
2016 Mk7 GTI DSG 64k miles. Recently I decided to tune my car so went and got a Cobb AP, putting their OTS stage 1 tune on and all. Problem starts immediately with WOT, as soon as rpm reaches above 5k the car would sound like a Subaru, throws EPC light and runs like crap until you turn it off and on again with P0304 Cyl4 Misfire,P130A Hide cylinder. Cleared codes and Flashed back to stock map, car runs fine even in full throttle. Thought it might be because of the tune so I went ahead and got a base tune from EQT, along with new rs3 coils and rs7 plugs gapped at .025 just to be on the safe side. However the same problem came back in exactly the same in WOT situation and same codes. Anyone experienced these problems and what would be the solution? I got some theory such as carbon buildup, bad PCV, or plugs need to be gapped more... I'm really lost here.
 

2slowvw

Moderator
Location
VA
Car(s)
2022 Tesla Model 3
it's running out of fuel


While this could be true its probably not what you are thinking. It's not that the fuel system is taxed, the injector could have a problem meeting fuel requirements. Maybe its is clogged up some, or has some sort of issue if you always see it on number 4.

You can try running some FI cleaner through to see if that helps, otherwise might need to swap out the injector. I can't remember who but i think @railroader had an injector go bad or had an injector issue.
 

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
I wont be able pull it until Saturday, bring me the bad news :( bad oil ring? Carbon buildup?

Clean the # 4 plug and put a couple thousand miles on it with the stock tune and check the plug again.
 

The Fed

Old Guys Rule
Location
Florida
I had 72,000 on my MK5 with the original stock plugs with stock coils with 40,000 miles and had no misfiring at speed despite a lot of carbon buildup. You usually get a rough idle, hard starting, and misfiring at idle on most or all cylinders with carbon buildup. Check everything on cylinder 4. Swap the coil for one of the others, then swap the plug. Make sure the threads in the head aren't screwed up and the plug is seated. If 4 keeps misfiring I'd do a compression check then check the injector. That's in the order of easy to hard. If you have VCDS you can check to see if the injector is cycling properly. Since you just changed the coils and plugs I'd bet on one of them being the problem.
 

duong1994

Passed Driver's Ed
Location
Phoenix, Arizona
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these has got to be 3 and 4, I notice oils are on both. These are the old stock plugs I replaced about 15k ago.
 
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