Hot start detonation 4.2 FSI
I actually have a Touareg, but since its 4.2 FSI far more common in the Q7, I thought I would ask here.
When the engine is at operating temperature, shut down for 1-5 minutes, and restarted, I can hear detonation. Hot starts almost seem too fast-- the knock happens on the 1st or 2nd crank, and the engine immediately starts after. It does not seem to happen again while running. Cold starts are always fine, but they take longer, after 4-5 cranks. I only run premium fuel. Octane booster does nothing. I've yet to try ethanol free fuel, but it's never needed special fuel before. Carbon cleaned ~10k miles ago. Does anyone else have this? VCDS does not indicate any problems, and I have no check engine light. |
Bumping. Nobody else with this issue? It seems to be getting worse and I'm concerned I'm eroding away my pistons/seals.
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Greetings,
Have you ever resolved the issue? |
I would suggest looking at your injectors. If one is leaking fuel and you try to restart the warmed up engine, you can hear that detonation. That doesn't always produce an engine light or any code. Hope this helps.
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Totally agree with KoJackee.
This injectors are crap. My car has the same behavior, when hot,if a turn it off an restart after a few minutes, it knocks. But in my case, I almost always hear 2 knocks. And don't bother testing them on bench: they only leak when hot. That's why it's hard to determine which of them are bad. I figure one of them by removing spark plug when engine are hot and, believe or not, I could hear the spray inside cylinder, coming from crappy injector. I replace it, and one of the 2 knocks at start was gone. Some time in the future, I will replace the other piece of expensive garbage. I let you know if knock stops. |
Have you replaced them yet? If so, are the symptoms of detonation gone? I plan on doing carbon cleaning and replacing all 8 injectors while I am at it.
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Originally Posted by hydrolocked
(Post 25187421)
I actually have a Touareg, but since its 4.2 FSI far more common in the Q7, I thought I would ask here.
When the engine is at operating temperature, shut down for 1-5 minutes, and restarted, I can hear detonation. Hot starts almost seem too fast-- the knock happens on the 1st or 2nd crank, and the engine immediately starts after. It does not seem to happen again while running. Cold starts are always fine, but they take longer, after 4-5 cranks. I only run premium fuel. Octane booster does nothing. I've yet to try ethanol free fuel, but it's never needed special fuel before. Carbon cleaned ~10k miles ago. Does anyone else have this? VCDS does not indicate any problems, and I have no check engine light. |
Originally Posted by KoJackee
(Post 25715251)
I would suggest looking at your injectors. If one is leaking fuel and you try to restart the warmed up engine, you can hear that detonation. That doesn't always produce an engine light or any code. Hope this helps.
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Originally Posted by legisus
(Post 25809453)
How it could be, gasoline not working without sparks?
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Originally Posted by KoJackee
(Post 25809456)
I believe if the injector is leaking after engine shut off, there is too much of fuel in the cylinder when restarting an engine which causes a loud detonation.
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