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What causes all 4 newish spark plugs to get carbon fouled

Jok3sta

New member
So the car is a 2010 GTI CCTA stratified tuned FBO with APR coils and NGK iridium plugs with about 5k on them. A few months ago, I changed the PCV diaphram with the RKX diaphram. Almost immediately after, the car started misfiring like crazy. Like barely running. So is decided to just change out the complete PCV with a new OEM one from the dealership. But the car was still running the same. Before the diaphram change the car was running fine. So I automatically assumed the main seal is shot and park up the car ( I had shoulder surgery recently and couldnt work on the car on that level ). So fast forward to a few days ago while doing a compression test ( 150 straight across }, I notice the plugs are ridiculously carbon fouled up as shown in the photo below. So i do quick clean on them and reinstall. And what do you know, the car starts right up and is running almost normal. On cold start it misfires a bit but once warm its smooths out and drives fine. Im for sure going to replace the plugs anyway but before i change them I want to know if anyone knows what would have caused this? Im still getting multiple misfire codes after a few starts because the car idles so rough when cold. Im assuming thats because the plugs are still pretty gunky? Since this happened those are the only codes I got, with the exception of a " leak in air intake" code. But i think thats from me not installing the intake to turbo coupler properly. I inspected the plugs again after driving it around a bit and they didnt get any more carbon on them after the quick clean. Thanks in advance for any help. Sorry for the long post.
20240602_164411.jpg
 

king1138

Go Kart Champion
That spark plug looks wet, which would indicate either fuel or oil. Carbon would be dry. Since all four plugs are fouled, I would lean towards oil. You may have lost a seal on the turbo, or the new PCV diaphragm may be faulty.
 

Alpinee30

Go Kart Newbie
+1 for oil
 

GolNat

Autocross Champion
Yeah that looks like oil. Check your pvc work you did since that was the last thing touched.
 

Jok3sta

New member
Thanks for the replies. Since writing this post ive gone over all the PCV parts and the car is running miles better. but the Air leak in intake system keep popping back up. So Im going to get a Smoke test done to see if i can find any leaks.
 

Alpinee30

Go Kart Newbie
Regulated compressed air and soapy water is better than smoke. It's the recommended test from VW service manual, not to not a smoke test. But if its massive it should show with smoke.

I've had a leak at the MAP sensor a smoke machine didn't show that leak.
If you have a regulated air compressor like say 15psi it's a DIY. No need to pay someone.

FYIW you'll get better info here than the other forum.
If you need a service manual, TSB, Diagrams etc. https://erwin.vw.com/erwin/showOrderFlatrate.do
 
Last edited:

Jok3sta

New member
Regulated compressed air and soapy water is better than smoke. It's the recommended test from VW service manual, not to not a smoke test. But if its massive it should show with smoke.

I've had a leak at the MAP sensor a smoke machine didn't show that leak.
If you have a regulated air compressor like say 15psi it's a DIY. No need to pay someone.

FYIW you'll get better info here than the other forum.
If you need a service manual, TSB, Diagrams etc. https://erwin.vw.com/erwin/showOrderFlatrate.do
thank you man. I appreciate the info. i gotta see if my compressor still works lol. Ever since going cordless i never use it anymore..
 
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