knock control on AQG

[oldnick]

knock control cyl 7 P1331 reg limit exceeded intermittent is the fault code I am getting

is there really a separate sensor on each cylinder ?
being a simple fellow I thought there was a sensor per engine or at most one per bank so what is this about and what to do ???

there must be some info about but can I find it ? can I ******

[Ameiseuk]

I thought there was one on each bank of cylinders?

[mattylondon]

Originally Posted by Ameiseuk

I thought there was one on each bank of cylinders?

Yes, that's my understanding as well.

[MikkiJayne]

Yes, one per bank, but the ECU knows which cylinder it just fired so it can work out which one just knocked as well.

There are measuring blocks for individual cylinder knock detection parameters iirc so you can watch it running and see what is happening, and plot it on a graph using VCDS. Swap the coil pack and / or spark plug to another cylinder to see if it moves.

[Ameiseuk]

Originally Posted by MikkiJayne

Yes, one per bank, but the ECU knows which cylinder it just fired so it can work out which one just knocked as well.

There are measuring blocks for individual cylinder knock detection parameters iirc so you can watch it running and see what is happening, and plot it on a graph using VCDS. Swap the coil pack and / or spark plug to another cylinder to see if it moves.

Ah, thats how it works...very clever.

[oldnick]

[quote=MikkiJayne;118912]Yes, one per bank, but the ECU knows which cylinder it just fired so it can work out which one just knocked as well.

There are measuring blocks for individual cylinder knock detection parameters iirc so you can watch it running and see what is happening, and plot it on a graph using VCDS. Swap the coil pack and / or spark plug to another cylinder to see if it moves.[/QUOTE

aha BUT
looking for parts it seems there are what are called blue sensors and green sensors ...presumably should be the same on each bank?

if I read this correctly the problem can be either

spark plug , coil pack OR knock sensor ?

tks MJ

[MikkiJayne]

S8s use 2 green sensors. One is in the V under the inlet manifold and the other is just behind the power steering pump. The 4-cylinders use one blue and one green.

I would say spark plug most likely, then coil pack, then excess carbon in that cylinder causing local hotspots and pre-ignition, then knock sensor. If it was failing one bank then sensor first, but since its one cylinder look at cylinder-specific things first

[27litres]

Originally Posted by MikkiJayne

I would say spark plug most likely, then coil pack, then excess carbon in that cylinder causing local hotspots and pre-ignition, then knock sensor.

I would add checking the spark holes for oil.
Based on D2 experience, coil pack failure is more likely than spark plug failure - though spark plugs are cheap! Swapping the coil with another cylinder is a good idea to test both.
The fact that's it's able to detect knock would almost straight away knock out the knock sensor as a fault (not sure if pun intended or not!)

To deal with carbon (and as general maintenance), add some injector cleaner for the next few tanks, and some octane booster (many products do both), along with the highest rated fuel available (98RON BP is good) and go for some long drives with a mix of highway and spirited driving to give it every chance to burn off.
This is a good to do on occasion anyway!

[oldnick]

thanks all for your comments
did a critical path analysis on what to do first ,started with taking a friend to catch his flight back home to canada , some brisk overtaking required to get past the trucks on the country roads