Cylinder 4 knock and knock control

[vwnut8392]

so as of lately im seeing 1-2 degrees pulled from cylinder 4 only when in boost. i have had problems with AAN chewing up rod bearings on 4 in the past but that was before i could see the per cylinder knock control. what i was wondering is if im seeing early indication of something failing on cylinder 4 or if i have a phantom knock issue?

i know PRJ said the stock knock control works perfect in 99% of applications PRJmod could be used on. i have not touched the knock control settings at all. i reduced timing from the mapping as low as 9 degrees advance and it did not show back up but thats far too low of a timing advance under boost to me. when i was knocking i timing was between 16-18 degrees advance. i did check and retorque my knock sensors to 12 ft/lbs as per the bentley manual specs but i figured if one was loose or over torqued it would trigger more than 1 cylinder. i have an oil pressure gauge in the car and i get 65-65psi on average driving under full boost at 26psi. those are the oil pressure numbers i have always seen since i installed the gauge over a year ago. i may end up pulling the pan and inspecting cylinder 4 rod and rod bearing for damage but im hoping to avoid that. engine runs perfectly fine under normal driving conditions. any thoughts on if this may be an indicator of some sort of rod failure or of 16-18 degrees timing with 26psi is just too much and only cylinder 4 is seeing the effects from it?

[newsh]

I had similar issues
I found a poor connection on an injector, the wiring plug was failing. I also ended up relaying my 044 fuel pump as the fuse in the fuse box was getting hot and melting.
I also replaced the knock sensors and torqued to 20Nm. One of them the plastic was cracked.

[vwnut8392]

Thanks for the input. i have not relayed my fuel pump yet and i do have a walbro 255 in tank. i will look over injector connectors. my knock sensor looked perfect still when i took them off before retoquing them.

[Error404]

If you are hammering rod bearings on that cylinder sounds like genuine knock caused by a hardware / tune issue to me. As Newsh says injector plugs and the engine loom are a common fault. Can you trim ignition / fuel per cylinder in Motronic? Why not pull timing / add fuel until you get to the bottom of it.

[Acki]

At the end he's tried to archive 3 bar boost with stock hardware :-D some cylinder will always start to knock first.

Not enough information to tell you anything.
From hardware perspective - a loss big-end conrod cap would cause knocking to the head - always.
To small oil film would lead to contact when the pressure raises in the cylinder. Don't know the exactly working of the knock routine but would expect some "knock window" function so the noise came "far" after ignition or you can hear it anyways and you ignore it. Conrod bearing damages you can exclude by rev up the engine a little bit, at some point the mass force of the conrod and the gas forces will equal - no bearing load - at the combustion cycle. At youtube you find enough videos.
Other noises (alternator for example) are also possible or mal function of injector.

I don't expect that you will have success when you tune the way you going now.
Too rich idle -> solution lambda correction...
I think you mismatched some maps and some malfunction is the result.
When I tune I would tune the mixture with a stron retarded ignition first - until mixture works as it shall.
Then I will advance the ignition until it knocks.
Tune finished in some simple words.
I would also start the tuning with a stock bin file (with prj mod).
Always start by the basics, always check the basics.

[vwnut8392]

At the end he's tried to archive 3 bar boost with stock hardware :-D some cylinder will always start to knock first.

Not enough information to tell you anything.
From hardware perspective - a loss big-end conrod cap would cause knocking to the head - always.
To small oil film would lead to contact when the pressure raises in the cylinder. Don't know the exactly working of the knock routine but would expect some "knock window" function so the noise came "far" after ignition or you can hear it anyways and you ignore it. Conrod bearing damages you can exclude by rev up the engine a little bit, at some point the mass force of the conrod and the gas forces will equal - no bearing load - at the combustion cycle. At youtube you find enough videos.
Other noises (alternator for example) are also possible or mal function of injector.

I don't expect that you will have success when you tune the way you going now.
Too rich idle -> solution lambda correction...
I think you mismatched some maps and some malfunction is the result.
When I tune I would tune the mixture with a stron retarded ignition first - until mixture works as it shall.
Then I will advance the ignition until it knocks.
Tune finished in some simple words.
I would also start the tuning with a stock bin file (with prj mod).
Always start by the basics, always check the basics.

what you are suggesting is what i have been doing. i started with stock PRJmod BIN and set my timing table that had 9 degrees advance when in boost. it was a flat even 9 degrees. the whole way across the board. my other car that is still on VEMS is running the same amount of boost out of the same turbo, essentially the only difference in engines is the other car has 7A cams. the other car has no problems and has been taking abuse for 4 years at 28psi on stock rods and pistons and its going strong after all these years of abuse. the other car is an 84 audi 80 quattro i swapped with an AAN in 2012. over all my S6 does have 482,000km on it and the bottom end has never been touched. i pulled the head off to inspect it for cracks in the combustion chamber around the spark plug holes when i bought the car and upgrade to 3 layer metal head gasket and ARP head stud kit. beyond that stuff the bottom end has never been opened since i've owned it. it may just simply be ready for a refresh the more i think about it because the documentation that came with the car dont show anything ever being done with the lower half of the engine.

[Acki]

Injector malfunction or loss conrod would be even make trouble when you run 5 degrees advance.

[vwnut8392]

injectors arent that old, maybe a year or so since i installed them. i will check the connectors to see if any have broken down from old age. last thing i will do is toss it on the lift, pull the pan and and start inspecting rod bearings. im running holset HX35's on both of my cars with larger than normal turbine housings, the torque onset is pretty slow with these turbos but the top end power is pretty insane. i learned from another post on here a long time ago that slow torque onset can keep a stock bottom end together for a long time and it will put out some decent power running at boost levels higher than most suggest running on a 20v. i tried it myself on my 80 quattro and was pleased with the results so the S6 got the same treatment too.

[Error404]

IME the injector harness can break down inside the harness jacket so I'd have a really good check over it, also disassemble all the injector connectors and check the inserts for damage (them get really crumbly over time).
HTH

[vwnut8392]

I think I may have just found the cause of the problem. My drivers side engine mount is ripped completely in half. I’m willing to bet if I replace that mount it goes away. The bracket on the engine lines up with cylinder 4 perfectly.

[newsh]

Might be that, I’m sure at some point I was seeing knock from the ISV banging on the Wagner inlet manifold

[vwnut8392]

Might be that, I’m sure at some point I was seeing knock from the ISV banging on the Wagner inlet manifold

i think im going to order a full set of engine and trans mounts from AKmotorsport in poland. once i get replacement mounts i will report back if that was the cause of my knock or not.

[prj]

Cyl 4 always knocks first, then cyl 3.
If you actually had shot rod bearings the ECU is correct.

If you have some sort of knock sensing error, then it will mess with all the cylinders that are listened to by the sensor, and it will be totally random, not on full boost, but just driving casually on part throttle.