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What is this sound? Broken spark plug electrode - clicks intermittently - need help

golfare

Passed Driver's Ed
Location
CT
Details about my car mods first:
2016 6MT Golf R, APR Stage 2 high torque, CTS high flow catted DP, APR intake, APR coils, RS7 plugs, Southbend Stage 2 daily clutch, stock intercooler.
61k miles, no carbon cleaning yet, plugs were at 12k miles.

The electrode from spark plug in Cyl 3 broke off. Car threw P0303 and P0304 (cyl 3 and 4 misfire) and P0300 (random/multiple cylinder misfire).

Compression, leak down test and cylinder boroscope visual check passed. No metal in the oil on the dipstick. Replaced the old RS7 spark plugs with new stock plugs, went back to the stock coils. Car ran totally fine for about 30 miles, babying it. Then I gave it a 1-2-3 pull with about 3/4 throttle and let off. Instead of hearing pops and bangs when I let off like I normally would, I heard a new ticking sound. Limping it home 1/4 mile, the sound came and went intermittently. Car threw P0301 and P0302 (cyl 3 and 4 misfire) and P0300 (random/multiple cylinder misfire). Pulled the new plugs, they all looked fine.

I disassembled the downpipe and did not find the electrode. Turbine blades looked perfect, no shaft play in the turbo. Started it with the catback removed in hopes of blowing any metal bits out. No luck. Perhaps the electrode was so small by the time it broke off that it disintegrated?

The noise:

After the noise happened with the new plugs and that one pull I did with them, every time I restart the car, the noise does not come back at idle. I think it needs to be higher in the RPMs to recreate the sound. Car ran totally normal with no bad sounds at idle. Ran it for about 15 minutes and brought it up to 2k without issue. Was too afraid to take it out of the garage to run it down the street as I ran out of free tows. I took off the PCV valve off to see if it was a loose/damaged rocker arm, could only see a couple of them, all looked fine.

My next steps:
1. Use boroscope in the PCV opening to inspect the remainder of the rockers arms / valve train components.
2. Change oil and look for metal bits
3. Reassemble, see if problem comes back and if it does, use stethoscope to pinpoint sound. It sounds like it is definitely top end, not bottom end sound.

What do you recommend?
 

Escape Hatch

Autocross Champion
Location
USA
Car(s)
Mk7 GTI
Good luck!
 

golfare

Passed Driver's Ed
Location
CT
Removed the PCV Valve to inspect some of the valvetrain. Nothing obvious seen with the boroscope.
 

AceHammer

Go Kart Champion
Location
NY USA
Car(s)
2015 A3
Check coil packs as well

Edit also good to note, cylinders 3 and 4 use the same knock sensor. So often if one is knocking bad it will show as both
 
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golfare

Passed Driver's Ed
Location
CT
Have you found anything?
I haven't found anything. VW said I would need a new engine, but there is no scoring on the cylinder walls, and it seems to be running normal, turbo is perfect, so I took it back from them. I'm too afraid to put it under boost or drive it at all currently since I'm out of free tows from AAA. So I'm still trying to figure out what to do.

With the fact that I ran these plugs 40% past their service interval using slightly more powerful coils, we suspect that the plug tip disintegrated to almost nothing when it burned up through the engine. I know some folks will disagree, but this is the opinion of a master mechanic friend of mine who sees plugs burn down close to nothing when they go past their service interval on cars like these. So that tells me *probably* why it ate a spark plug tip.

However, I'm still at a loss why I got that ticking noise towards the left side of the valve train after I put it in boost and let off. Normally when you let off with the Stage 2 APR tune (pops and bangs), you get pops and bangs. Not this time. I got the same valve train-area ticking noise again.
When trying to recreate that sound when I got it back into my garage, we didn't push the engine past 2,500 rpm, and the noise did not come back. However, when using a stethoscope, the splitter part that leads to the PCV valve makes a similar tapping sound with the same exact rhythm as ticking sound in the video I shared. Could this just mean I'm getting this sound because of carbon buildup? I performed a PCV valve 'paper over the opened oil fill' test and it seemed to pass. Keep in mind I'm at about 61k miles.
 

AceHammer

Go Kart Champion
Location
NY USA
Car(s)
2015 A3
The splitter part that runs off the PCV is to the evap system, it's called the N80 valve could try replacing it.

I'd also suggest swapping the PCV out. The stock ones really don't like high boost and Stg 2 is right at the limit of when they can fail.
 

golfare

Passed Driver's Ed
Location
CT
The splitter part that runs off the PCV is to the evap system, it's called the N80 valve could try replacing it.

I'd also suggest swapping the PCV out. The stock ones really don't like high boost and Stg 2 is right at the limit of when they can fail.
Here's an update. A fellow MK7R owner with RS7 plugs who ran them past their service interval had the same problem as me. He experienced the same intermittent clicking sound as I did. His boroscope inspections of the cylinder walls also checked out fine and so did his compression test. He removed his intake manifold and found the broken spark plug strap in the intake manifold.
 

adgainai95

New member
Location
Melbourne
Car(s)
Golf R wagon
Here's an update. A fellow MK7R owner with RS7 plugs who ran them past their service interval had the same problem as me. He experienced the same intermittent clicking sound as I did. His boroscope inspections of the cylinder walls also checked out fine and so did his compression test. He removed his intake manifold and found the broken spark plug strap in the intake manifold.
beru or ngk?
 
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