Misfire in cylinder 3 only under high load/boost


New member
Hey everyone, I’ve been through countless misfire threads on here and other forums and can’t seem to figure out mine.

Car is a 2012 Golf R with APR Stage 2+ tune, along with all supporting mods.
Car currently has 142,5xx miles.
Running a pcv delete.
Changed spark plugs and swapped coils with no change.
Motor was rebuilt at around 100k miles due to losing compression in a cylinder due to a split second money shift. In the rebuild, I added APR’s valve train upgrade.

The misfire only appears to happen under heavy load after 4k rpm, and only when the car is attempting to reach full boost. I can sort of sneak the car’s rpm to over this with no issue, but as soon as the load increases to where boost wants to go all the way, it stutters like fuel cut from traction control kicking on or something.

Over the time I’ve had the issue, it has only thrown an actual misfire code once. All other times the only way I could see it is via live data from my obdeleven pro.

At this point, my intuition has me eyeing three things to consider:
First, a compression test. Seeing as Ive been through it before with this car, I’m hoping I have other things to try before this. While I feel confident that the motor “feels” fine in all other circumstances aside the above, I don’t actually know if that’s logical or not.
Second, a bad injector. As far as I can tell, they’re the originals. But based on what I read, I would presume a fuel related code would pop up but none have. Are there channels I can see live that would indicate an issue with an injector?
Third, a boost or vacuum leak. I have a pcv delete that has basically made the related issues go away since the rebuild. I don’t hear any noise that sounds like an obvious leak but I also don’t hear the whoosh from the DV as prominently, though I assumed that’s because the fuel was being cut due to conditions. Could totally be off though.

If anyone has any suggestions on which direction to go based on the above, I would greatly appreciate it!


What are the gaps of the plugs set for? You might try bumping them down by 0.1mm from where they are (roughly); (0.8mm)0.031" down to (0.7mm)0.028"__or 0.028" down to (0.65mm)0.025".

I wouldn't think the intake valve buildup is much after 42k miles, but it's not something to abandon just yet.

Yes, a compression test may be in order...or just jump ahead to a leak-down test. Compression specs are:

I don't know if OBD11's MB's are the same as VCDS. In VCDS, for viewing or logging fuel pressures (both high and low), I use MB's 230 and 231. I prefer a MB for the low pressure which shows the Load% the LPFP is working for both at idle and throughout a rev range run. If the car and OBD11 will allow it...log the fuel data from 2k rpm to redline, but at least check the LPFP pressure and Load% at idle. If you feel it stumble during a data run, make a mental note of the rpm you noticed and look at the fuel data for what it was reporting at the same rpm. You can or should also test it and see if the fuel rail is holding fuel pressure (video link added). This should show if an injector is not shutting or if the pressure limiting valve prematurely leaks fuel into the low delivery tube. Make sure the engine is up to temp, then maybe park it in a garage to retain engine heat better, and then shut it off; watching a MB showing fuel rail pressure data.

I hate seeing the PCV delete or catch-can on a daily driven car. Those are both OK for when it's been dedicated as a track car and is then mostly driven in boost. But having deleted the application of vacuum to the crankcase for removing the PCV-to-inlet manifold tube, this (PCV delete or catch-can) reduces the benefit of improved sealing at the crankcase seals, valve guides and seals, and piston rings. I think it better to just keep a proper working PCV on it.


Go Kart Newbie
Are you sure the plugs are the correct heat range and gap? APR specs BKR8EIX at .024" for stage 2.


Autocross Champion
Are you sure the plugs are the correct heat range and gap? APR specs BKR8EIX at .024" for stage 2.

I'm Stg3 and ran a set of BKR8EIX plugs at .024 because at the time that's what I found from APR, no issues or errors but plugs looked like garbage when I replaced them after about 10k miles (heavy black fouling). Last time I looked APR had removed any gap recommendation from their website and only info is on forum posts and even that contradicts often. The ones I pulled out before installed by PO were at .032 and looked nice and grey, similar mileage. I replaced the fouled ones and left them at .032 and going to see, they only have about 4k miles on them now but plan to replace them at the end of the year at the latest due to planned heavy track use this year.

If there are no misfire codes I would put my money on something else, if you are noticing power loss but the ECU is not seeing it as a misfire to even set a soft code in history that would be odd. I would start with checking fueling as ROH ECHT suggested, even pulling the plugs just to check them and see condition, check for fuel smell in cylinder and on plugs.