Hi all,
Signed up to share what I experienced with a similar situation so far. I know this thread is long in the tooth, perhaps I will create a new post, but this thread helped me so far so I wanted to contribute.
My 2017 GTI Sport with Performance Package is about to hit 70K miles, a lot of highway, it is stock with the exception of the clutch that failed which was replaced with a stage 1 (forget the brand, although it lacks springs and is noisy as all get out) and the brakes and rotors because it was cheaper than OEM.
I had a steady CEL with the 'cylinder 2 misfire' code happen almost 5 months back, but the engine didn't feel like it was struggling or seem out of whack, so I cleared the code with a 20 dollar Amazon code reader and waited for it to return.
It didn't seem to, so I thought things were all good.
Fast forward to a few weeks ago, my car starts shuddering when I put the accelerator down more than slightly in the RPM range of 1500-3000. The work around was either feather the pedal slightly, or upshift to get to the higher RPMs.
I couldn't get another CEL so I wasn't sure where to go, until 2 nights ago. I was traveling for work and finally got a flashing CEL briefly when giving the accelerator a heavier push on the highway. It disappeared but I was looking forward to getting back home to use my cheap scanner to figure it out.
On the way back home from my work trip, I had to upshift and give it the beans on the highway, and the car was not happy, a steady EPC light (does it ever flash?) and CEL flashing, but not stopping, I went back to cruising and feathering the accelerator, and the CEL became a steady light.
Before continuing on, I stopped at Autozone and used their code reader, and what greets me? the 'Cylinder 2 Misfire' code returns! (I forgot the number, sorry).
So I carefully continue, eventually making it home and parking for the night.
The next day, I get to work removing the coils and plugs, starting with cylinder 2 and am greeted with this:
So I ended up at this thread.
I removed the remaining plugs and the layout looked like this (cylinders 1-4):
Now on to the cylinders, I am awaiting a 24mm socket to come in with some other items as I was preparing for doing a walnut blasting thinking that may be the issue, as such, I am unable to cycle the cylinders outside of running them for the compression test, more to follow on that. Excuse the pics quality.
Cylinder 1 piston face:
Cylinder 1 wall:
Now for the fun part.....cylinder 2, or known as far side of the moon:
Cylinder 2 wall:
Cylinder 2 Fuel Injector:
Then we have cylinder 3, another interesting entry:
Cylinder 3 wall: Sorry, don't have the shot, but it looked similar to all the others.
Cylinder 4 face (I think the lights on the boro were covered in sealant):
Cylinder 4 wall:
I ran a compression test and the results were as follows:
1: 175 psi
2-4: 180 psi
So cylinders 1 and 4 look pretty good, 2 and 3 look like the bottom of the oven when food falls on it, but the cylinder walls look similar, once I get that socket, I will cycle each piston again and take look at the entire wall.
I replaced all 4 plugs with OEM, put the coils back in swapping 1 and 2, started it up, and everything seems fine. I took it out to the highway, recreating the conditions of more than slight acceleration in that low RPM range, no bucking, no CEL, everything seemed good.
I am still very concerned about where the electrode went, but it's not in the cylinders. I do still plan to remove the intake manifold and move forward with the walnut blasting. I will be sure to check it fully and document that process too.
My luck with cars is never that good, hence why I have decided not to purposely modify beyond stock, no tuning for me. I modified a wrangler with 20k worth of stuff that never got me anything back, so I am content with what I have here on the GTI. But I feel like the broken electrode was product of another issue and not the cause.
When I pull the manifold for blasting, I am thinking about pulling the injectors to scrub the face, but cylinder 2 looked the worst (I can only attach 10 pics, so the injectors are the odd pics out)
The things I don't understand include the following:
-IF the missing electrode was the culprit, why did the engine seem fine in so many other instances besides the slight acceleration? I would think the CEL would be flashing all the time and I'd have more codes like 'hide cylinder'
-WHAT the HECK is going on with the differences in piston face appearance between cylinders 1,4 and cylinders 2,3? I would probably need to remove the head to get in and clear that stuff out, if it's even worth it.
If you took the time to look at all this, I hope something helped you. If you provided feedback, thanks in advance! If you have questions, please let me know and I'll try to answer them to the best of my limited knowledge.