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Shawn

Knock knock

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I was doing some logging of my car (2012 Audi S4 with a 3.0 V6 with a roots style supercharger) on the stock tune and I am seeing some pull from knock detection. Some cylinders are worse than others and it isn't 100% consistent in how many degrees of timing gets pulled. I can do a series of 3rd gear pulls and each one will have differing results. The one bank is worse than the other but I have logged a bunch of things like cat temp and egt and both banks look the same in that regard. I also can't find anything yet that suggests something is rattling or causing false knock. But maybe I missed something. 

It has been suggested that it is carbon deposits in the combustion chamber. I tried to scope the cylinders but the camera I had wasn't the greatest and I didn't have to ability to rotate the crank to get a good look with the pistons at the bottom of their travel. But it does look like there is some decent buildup. I just don't know if it is a problematic amount. Regardless, cleaning it would be the first step. A month ago I ran a tank of fuel through with some BG 44K cleaner through but I didn't really notice a difference. Car has all new plugs and coils. The knock detection starts to come in at 45% throttle a bit but mostly at WOT. If I wasn't logging the car I would never know. But the issue is preventing me from tuning my car as the knock detection gets too high with the tune so I backed it out.

As the engine is direct injection I know there is an issue with carbon on the tops of the valves and I do plan to do the walnut blasting to clean it up but I doubt that kind of buildup would cause the issues I am seeing in the logs. Am I wrong about that? 

I have been scouring the internet to see if there is a way to clean the combustion chambers without having to disassemble the top half of the engine. If it is possible. Not sure if gasoline additives will really work or maybe I'd have to run a dozen tanks of cleaner through to get decent result?

Any advice, insight or suggestions would be greatly appreciated.

 

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Walnut blasting has become normal routine procedure for many di motors for a reason. I could see deposits causing pinging. Hotspots on the pistons or valves can lead to predetonation. The deposits can be worse bank to bank dependant on runner length and flow characteristics in the intake manifold and runners. 

I’ve heard shell fuels are the best as the detergents help prevent it, and shell has the most detergents/additives. 

Is this common to the Audi v8? Have you looked at others reports on blasting?

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It is a known problem on my V6 and until I pull the supercharger to get to the top of the valves i have no idea what the condition is. At least that part is not a terrible job. The cleaning is time consuming though. Guys on my S4 forums have been made 3D printed adaptors to fit in the intake that allows you to hook up a hose to a vacuum and put the blasting gun in to keep it low mess.

But I am encouraged if that might cause the problem but I was sceptical and thought it would have to be something in the combustion chamber itself. 

 

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Stupid question time...

Have you considered the possibility to be false KR?

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11 hours ago, Shawn said:

It is a known problem on my V6 and until I pull the supercharger to get to the top of the valves i have no idea what the condition is. At least that part is not a terrible job. The cleaning is time consuming though. Guys on my S4 forums have been made 3D printed adaptors to fit in the intake that allows you to hook up a hose to a vacuum and put the blasting gun in to keep it low mess.

But I am encouraged if that might cause the problem but I was sceptical and thought it would have to be something in the combustion chamber itself. 

 

I have a bag of walnut media I’d let go for not much. I did the bmw while the head was off and didn’t use much. 

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6 hours ago, nopistons said:

Stupid question time...

Have you considered the possibility to be false KR?

Yup. I just haven't found the source of it. Unless the sensors were faulty. I was trying to see if I could see any damages wires but couldn't. The knock sensors are under the supercharge of course. And I don't see anything else rattling around but will have to check more once the car is up on a lift again.

5 hours ago, Brian_Earl_Spilner said:

You said the car has all new plugs... How did the last plugs look? Fouled?

Did the new plugs need proper gapping?

Old plugs looked fine as far as I could tell. The new plugs say they don't have to be gapped but I did to make sure they were consistent. I gapped them to the tuner's spec which is a bit tighter than OE spec. That said, In my one test where I I left 3 of the plugs in and cleaned and regapped the other 3 (to the tuner's spec), the regapped plugs seemed to perform a bit better.

2 hours ago, MRS Joe said:

I have a bag of walnut media I’d let go for not much. I did the bmw while the head was off and didn’t use much. 

Cool. I do have some of the fine grit. Do you know if you have coarse or fine? If it's coarse I might snag it from you.

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I thought electrical issues a no charge extra with BMW? Didn't know Audi also included that with the base package. 

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I switch between Shell 91 and Husky 94. I prefer Husky 94 from the octane perspective and I can see that the car has noticeably less knock timing pull with the 94. I am actually back on Shell 91 and have logged my car again after another can of BG 44K and no improvement. Actually it is worse now because of the lower octane. The car was 3 years old when I got it so I have no idea what was used before. And from what I have been reading, most top tier fuels (I know Husky is not top tier) won't clean the engine but simply might help maintain it better.

I keep scouring the internet to find how I can clean the combustion chamber without taking the heads off. I found some videos of a product called Heavy Metal that looks like what I am thinking of but have not found a mainstream solution (if you look at the videos you will see what I mean about not really mainstream).

I don't understand how if carbon buildup is such a big think for DI cars, why is there not a service industry built around it. I have Audi Winnipeg currently investigating what could be done because the service adviser didn't really know of such a procedure, but then again, he did not seem to really be familiar with what was involved in the carbon cleaning solution they do offer (walnut blasting).

Simply due to lack of time is the only reason that I have not yet pulled my supercharger to at least see what the carbon buildup is on the tops of the valves and maybe take care of that part of it. Maybe it would help, depending on how bad it is.

It is interesting though that if I was not logging my car, there is no indication that something is wrong. It pulls hard, no hesitation. The only thing about the car is a somewhat rough idle which is an odd normal characteristic of this car.

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