Quick Knock/Clunk When Starting M56?

[AlphaSnacks]

Does anyone else have this issue? Mine comes and goes. Stock ECU or tuned ECU. Weather doesn't seem to make a difference, either.

Sometimes as I start the car, while it's cranking/turning over it'll make one quick knock noise and start up. There's no delay or hesitation to start, and the car idles, drives, etc. perfectly smooth. But it's always concerned me that the car does this on and off.

Perhaps a similar issue that occurs with QX56 owners?

[adeedpb]

Is it a knock like the starter teeth hitting the flywheel or more like a knock inside the engine?

[AlphaSnacks]

It sounds like it's inside the engine. Kind of like when an old car would knock as it ran out of gas and stall out.

It could be a delayed spark issue, perhaps needing a new plug?

[adeedpb]

Something plug related would be more of a ping. I doubt it would be rod knock, these engines are pretty tough and you have a new car. Could be something simple, I would definitely bring it up to the dealer at the next oil change, at least have them check it out.
But good luck with getting a definitive answer, I am still trying to convince them I hear pinging sometimes.

[AlphaSnacks]

Yeah, it's definitely not rod knock. That just sounds awful.

It is a ping, which is probably spark or injector related. I noticed if I drive the car hard and heat it up, it won't ping when it turns to start the next time. But if I drive it like a pansy, it's more common to occur as carbon may be building up.

The other day I drove the car in 3rd and 4th at highway speeds, 90-degree day. Parked it for an hour, restarted it, and perfect start all day.

Audis have these issues a lot, and they are direct injected like the VK56VD is. BMW N54/N55s too. They get carbon buildup around injectors which causes a poor spray, which then causes some issues with the spark. What these guys have discovered is if they beat the piss out of their cars for about 30 minutes, it has the same effect as a carbon cleaning, because the internal heat breaks apart the carbon inside (this is also why our cars blow so much soot).

So what I'm going to do is keep driving my car hard, use a bottle of Techron/Chevron fuel system cleaner as well since it helps in breaking apart the carbon. I'll follow up.