Catastrophic engine failure

[Billman]

When you take away the ability of the knock control to react to the knock, this is usually what happens.

many stock engines also....sensors get old, sensitivity is also debatable....of course is nice to have working knock control but if it was so good Audi's recommendation i.e. for the RS2 would not be 98 fuel and if you must fuel 95 then take it easy and avoid full throttle and runs above 4500 RPM (or so).

[prj]

i know of NO sane tuner that deliberately does that on an ECU that can control knock. Those who do, should be avoided!

That sadly includes more than half of all the tuners around...

many stock engines also....sensors get old, sensitivity is also debatable....of course is nice to have working knock control but if it was so good Audi's recommendation i.e. for the RS2 would not be 98 fuel and if you must fuel 95 then take it easy and avoid full throttle and runs above 4500 RPM (or so).

Sensitivity is very good. Too good actually, it detects knock sometimes when there is none, above 400hp knock sensitivity needs to be re-tuned...
The recommendation is mainly due to performance concerns. An RS2 will run on 95 RON, it won't blow up your engine or anything...
As for stuff getting old - yeah if the knock sensors are not installed correctly or not picking up the right frequencies anymore, then the system will fail.

[A80Avant]

are you referring to motronic tuners? cause most aftermarket systems dont have adequate knock senssing, so tuning is done differently. But if you are talking about motronic tuners, how do you know? Have you seen maps from half/all of them or have you spoken to them?

[Keeper of The Kitten]

Lou, I was away from home when I first read this and a very busy boy, but now I'm home I want to say sorry to read about it - I do hope you'll get your S2 back on the road.

[prj]

But if you are talking about motronic tuners, how do you know? Have you seen maps from half/all of them or have you spoken to them?

Very stiff springs or no N75 boost control = basically no knock safety.
Timing pull alone is not really enough... and the system is not designed to save your engine by timing pull.

[A80Avant]

ah, ok you are talking about an indirect reduction of safety then. I would say 'best guessing' timing pull is even more destructive than a stiffer spring.

[prj]

ah, ok you are talking about an indirect reduction of safety then. I would say 'best guessing' timing pull is even more destructive than a stiffer spring.

No, it's a very direct reduction of safety.
Especially on tuned engines.
As you pull timing, your EGT's rise. To prevent excessive EGT rise it slowly reduces boost.
It works in tandem - boost reduction and timing pull. If you take away it's ability to reduce boost when needed, then as you pull timing your EGT's spike, the combustion chamber gets even hotter, and it starts a very bad chain reaction of events - it pulls even more timing, and it gets even worse...

And then people blame Bosch for bad knock control.

[Billman]

Timing pull alone is not really enough... and the system is not designed to save your engine by timing pull.

AFAIK it does not cuts boost. Or does it pulls timing to let's say 10 degrees in steps and then cuts boost?

[prj]

AFAIK it does not cuts boost. Or does it pulls timing to let's say 10 degrees in steps and then cuts boost?

It slowly cuts timing, after a certain threshold which is adaptive (it learns continously) it pulls some boost, then continues pulling boost and pulling timing. Once a knock-free operating state is reached it gradually steps up timing and boost.
During this entire process it learns and remembers in memory how much boost and timing it needed to pull to reach knock-free operation. The timing pull is individual for each cylinder.

If you take the ability to pull boost from the system, it almost completely loses it's operational capability, especially during heavier knock on high revs and higher loads where pulling timing without reducing boost does just as much harm as it does good.

If you look at ME7.1, not that much has changed. Perhaps the fact that it additionally has frequency control, whereas M2.3.2 has narrowband knock sensors, which are tuned and produced specifically for the engine. And the fact that it has an electronic throttle, so it can override the human factor before the engine is destroyed.

There is a bosch patent document from that time describing exactly how this adaptive closed-loop process works.
Also, if you read any decent book on forced induction which deals with knock control, it will explain all of this and why it is a very bad idea to only pull timing in a FI engine.

[A80Avant]

Of course you do know that EGT rise when timing is being reduced is because part of the flame of the combustion is done whilst the exhaust valves are open and therefore the heat in the chamber is less, not more in the combustion chamber...

Going a lot off topic again.
I hope the engine gets replaced soon!

[prj]

Of course you do know that EGT rise when timing is being reduced is because part of the flame of the combustion is done whilst the exhaust valves are open and therefore the heat in the chamber is less, not more in the combustion chamber...

My bad, not combustion chamber, temperature at the exhaust valves is what I mean, thus heating up the turbine. The more it is retarded, the more the turbine is heated.
In an already tuned engine, which is pushed far, this can lead to a downhill spiral, as stated earlier.
In M2.3.2, EGT is approximated as a function of engine operating parameters, rather than measured directly. Also Motronic's knock control is not meant to work on timing retard alone - it's meant to also pull boost during more severe knock, to further reduce knocking as well as control EGT. That's why it doesn't work properly when boost is not controlled by the N75 anymore.

Anyway, enough of OT.
At the end of the day - taking any system, bringing it outside it's operating parameters and then blaming it on the system is not the right way of thought.

[220bhp]

If my engine had a problem with injectors or knock sensors, surely I would have felt it running badly.I have had a failed front knock sensor before and the car ran badly with no boost.
As I said earlier the injectors are fairly new bosch green rs2. Both the knock sensors are new and tourqed correctly a mrc,fuel fillter was also replaced.
Would not any of these issue have shown up when the car was mapped, even though the car did ot make the power MRC thought it should, the car still ran well.

[220bhp]

The engine came out today and I, managed to take the sump of. Number three conrod is missing and the other four ar all turning with no apparent damage,the block however has a hole right through it. no 3 piston was still in the bore but with no skirt.
I .could only find the conrod cap and 1 bolt to go with the top of the conrod I retreaved from the engine bay,the rest is missing.
The head appears to be unmarked, but you can see marks on the piston that show contact with the valves.
I will post some pics asap, did not have my camera today.

[Billman]

I think the number 3 cylinder is the most prone to knock.

[Phil Payne]

Number three conrod is missing ...

#3 big end is usually (read almost always) the first bearing to go in a catastrophic oil pressure loss event.

So much so that I have for years now Plastigaged it as my absolute first measure after the oil pickup pipe is out of the way.