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Constant fouling of plug on cylinder 3

Caymanjp

Passed Driver's Ed
Location
Grand Cayman
Car(s)
2008 3DR Golf GTI
Hey everyone recently my GTI has been misfiring terribly. I replaced the coil packs and no change whatsoever, I am getting a cylinder 3 misfire fault. I see cylinder 3's plug is fouled with black wet looking deposits, other plugs look normal. I changed the plug but it's fouled again. Recently serviced car has had no issues otherwise, just a sudden issue I started having. Hope the picture helps, was probably the clearest I could take with my phone. Thanks in advance for any help

My vehicle is smoking too suddenly so obviously burning oil. Only on the 1 cylinder,
 

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ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Are the new coils; genuine VW?

What plug is that? And its code please? E.g.: NGK - PFR7S8EG. It looks to not be the correct type plug.

I would suggest having the intake valves cleaned. Generally, when sooting envelops the center electrode it is possible to be caused by poor valve seating or it has excess oil coming in. But you can't rule out problems with ignition. The coil harness may have a wiring issue for the #3 coil lead.

Swap the 'wet soot-#3 plug' into another cylinder. After driving long enough, check the new #3 plug and see if it has been covered in wet-black soot...and also look at the previous #3 plug to see if it has burned itself clean while in another cylinder. Then, if the new #3 plug is now oily...go ahead and swap the #3 coil onto a known cleaner plug and replace it with the coil from the other cylinder. After a while, see if the coil swap now makes the plug in cyl.#3 clean...and if the coil placed onto a known clean plug is now covered in wet-black soot. If you find the plug installed in the #3 cylinder is always the one covered in wet-black soot...then it has an issue with valve seating or excessive oil entering the combustion chamber.

I would not drive it much while it is in this state. Fuel wash from a badly leaking injector can wreck the engine. And if an intake valve is not seating, the flame will shoot into its plastic intake manifold and melt through it.
 
Last edited:

Caymanjp

Passed Driver's Ed
Location
Grand Cayman
Car(s)
2008 3DR Golf GTI
Are the new coils; genuine VW?

What plug is that? And its code please? E.g.: NGK - PFR7S8EG. It looks to not be the correct type plug.

I would suggest having the intake valves cleaned. Generally, when sooting envelops the center electrode it is possible to be caused by poor valve seating or it has excess oil coming in. But you can't rule out problems with ignition. The coil harness may have a wiring issue for the #3 coil lead.

Swap the 'wet soot-#3 plug' into another cylinder. After driving long enough, check the new #3 plug and see if it has been covered in wet-black soot...and also look at the previous #3 plug to see if it has burned itself clean while in another cylinder. Then, if the new #3 plug is now oily...go ahead and swap the #3 coil onto a known cleaner plug and replace it with the coil from the other cylinder. After a while, see if the coil swap now makes the plug in cyl.#3 clean...and if the coil placed onto a known clean plug is now covered in wet-black soot. If you find the plug installed in the #3 cylinder is always the one covered in wet-black soot...then it has an issue with valve seating or excessive oil entering the combustion chamber.

I would not drive it much while it is in this state. Fuel wash from a badly leaking injector can wreck the engine. And if an intake valve is not seating, the flame will shoot into its plastic intake manifold and melt through it.
Thank you very much for the detailed post, I appreciate you taking the time to type it out. Yes the coils are Original VW, I bought a spare set not too long ago just incase I ran into coil pack issues. The plug in the image is in fact cheaper Autolite plugs I purchased from the parts store since the car keeps destroying the NGK's I put in. Simply switched from a cost perspective until I get the issue resolved. The original plugs that were in are NGK 06H905601A.

I did indeed switch coils to try and see if the issue moves but it has consistently stayed on the #3 cylinder. Changing the plug, led to a misfire on the cylinder with the dirty plug. I cleaned it with abit of brake clean and thoroughly dried it. Re-installed and it seems to burn and clear up okay, but after a day of driving I start getting misfires again and the plug in cylinder #3 will be oil fouled. I keep getting told to change the valve cover gasket but I dont have oil in the spark plug tubes or on top of the plug. Oil is only on the combustion chamber side.

Vehicle only has about 90K miles so I'm leaning towards valve issue since smoke is only on occasional start-up and not constant like I would expect from piston rings. I'm just trying to figure out what would be worst-case scenario for repairs as this is my primary vehicle at the moment. Thanks again for taking the time.

JP
 

Caymanjp

Passed Driver's Ed
Location
Grand Cayman
Car(s)
2008 3DR Golf GTI
It's time for a compression check. It isn't the spark plug or coil.
That is my next step, would my compression be worse if it was piston rings compared to valve seals? Wondering how I can pinpoint one issue and eliminate another. Thanks for the reply
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
I would skip the compression test and instead, do a Leak-down test. It's your choice...if you do a compression test and are prepared to replace or rebuild the whole engine should it fail.

Compression test will, yes, tell you it loses pressure...but doesn't tell you where. It is just an additional test you will perform, and you will still need to do the Leak-down if you only want to determine if just the head or the block needs work.

The Leak-down test will pressurize each cylinder at TDC. If the pressure drops, you can tell if it leaks into the exhaust, the intake, or the crankcase. If you find a cylinder or more leaking, but not into the crankcase, then you will only need to rebuild the head.

I'm not sure I would jump to a conclusion yet, until the intake valves are looked at and cleaned if necessary. But again...your choice.
 
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