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Discussion Starter #1
2008 V8 FSI

When the engine is at operating temperature, shut down for 1-5 minutes, and restarted, I get detonation about 50% of the time. It's only one or (rarely) two pings, and does not seem to happen again while running. Cold starts are always fine. I only run premium fuel.

Does anyone else have this? What about in Q7s of the same age?
 

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Discussion Starter #3
Update: "Top tier" seems to mean nothing for my particular problem. Octane booster, though, has stopped this from happening. I used 104+ by Heet. Will update again once I can test with a full tank of ethanol-free without additives.
 

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FSI is bad for carbon buildup. Look for some of the de-carbon threads for more info.
 

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Thanks, but it was carbon cleaned less than 10k miles ago, and when it was gunked up it had no symptoms at all. I'm starting to suspect the cleaning has caused it, somehow...

EDIT: I spoke too soon. The octane booster has not solved the problem. Back to the drawing board.
 

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Coil packs, plugs? Possibly oil in spark plug tubes. This happened to both our FSI's. I replaced both engine's valve cover gaskets and made sure mating surfaces were super clean and everything tightened to specs and still had oil in tubes with spark plugs and coils soaked with oil. Off with valve covers again and used RTV to seal the gaskets when I put it back together.
 

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^^Truth in the above. Pull the coils and plugs and look for any tell tell signs.

The valve cover gaskets are prone to leaks in both versions of the V8 engine. The internal o-ring type gaskets (that seal the spark plugs) often go bad as mtnride described.
 

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Discussion Starter #9
No go. Pulled the coilpacks and there's not a trace of any oil in the spark tubes. While I'm glad my valve covers aren't leaking, detonation can cause much more expensive damage, so it's a bummer that wasn't the answer.

mtnride mentioned the coilpacks specifically. There are painted dots on some of mine from the previous owner. I think I know what that means. Can faulty coilpacks cause knocking?

Hoping to hear other suggestions. Thanks
 

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Discussion Starter #10
Ethanol free fuel did not help me here. Still looking for an answer. I'm due for a spark plug changed based on mileage, so will see if there is any improvement.
 

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Discussion Starter #11
Gave up trying to find the cause myself and took it to a VW dealer. Two in the shop and VW was unable to diagnose. They are flying in the regional traveling tech to have a look.
 

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What I thought was detonation (and corroborated by my indy shop telling me it sounds like detonation) was in fact coming from the HPFP. This is why there were no associated codes. The dealer recommended replacement of both for $1k and I agreed to the work. They are "100% certain this is the cause".
 

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HPFPs replaced, dealer reports the noise is still there! Waiting to hear about escalation. At least they didn't hand it back to me and leave me to discover this on my own.
 

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Discussion Starter #14
$1500, two new HPFPs, and two new fuel pressure regulator valves, no resolution. If this is happening to you and you're at the point of throwing parts at the car, consider starting somewhere else first and working back to these parts.
 

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$1500, two new HPFPs, and two new fuel pressure regulator valves, no resolution. If this is happening to you and you're at the point of throwing parts at the car, consider starting somewhere else first and working back to these parts.


Any updates?


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