knock control question

[bernsaudi]

If one of our cars has been mapped whilst running 98 octane fuel and then ends up on 95 octane fuel will it run without problems until better fuel is found. Can the ecu cope with the poor grade fuel? Please can someone move this to the right place, somehow I ended up in the for sale section

[Nik0las]

probably it will but I wouldn't run it on full boost

[bernsaudi]

My point being that as it has knock control on the ecu it should cope with the differences in fuel grade automatically or so I thought.

[spink]

It will cope with it but will reduce performance and mpg(-2 or 3) and also you will quite likely here it pinging now and again.Will be ok if its all you can get but not worth running on it to save money imo

[prj]

It will be fine, but if you want to always use 95 RON, it is better to map the ecu on 95 RON.

But yes, it will work perfectly fine - even cars I've mapped to 600nm on stock rods have taken a trashing at 95 RON and nothing bad has happened, but obviously there will be a ping every now and then, as if there is no ping, there is nothing for the ECU to react to.
Richard's car is a good example.
And yes, you will have less performance and worse MPG, so no point to use it in hopes that it will be cheaper.

If you put 76 RON in there, that is of course a different story...
Also, this assumes some clown has not disabled knock control in your ECU. I don't do such stuff

[bernsaudi]

Why is it better to map it to 95 ron? Surely the ecu with knock control can be mapped on 98-102 ron and the ecu should still adapt down to compensate for the lower grade 95 ron usage, otherwise it seems to me the knock control is not doing its job.

[Jamo]

For knock control to work your engine has to knock in the 1st place if you run 95 map it to 95 and if you put 98 in the ecu will advance it
Doing it in reverse is asking for trouble

[prj]

For knock control to work your engine has to knock in the 1st place if you run 95 map it to 95 and if you put 98 in the ecu will advance it
Doing it in reverse is asking for trouble

Sorry, that is not how it works.

The car is mapped to a certain octane level, it should not normally knock.
If there is knock, ECU retards ignition timing per cylinder, if there is persistent knock it will enrich fuel / switch maps, if it still is knocking, it will pull boost.

So when you are running on 95 RON, ECU will see that you get knock pretty much constantly and because it won't be able to compensate for it by individual cylinder timing pull (it will reach threshold on a cylinder), it will automatically switch to a lower octane ignition map and enrich fuelling up top.
Some knock is always normal in every engine, the question is how strong it is.

After some time, it will attempt to switch back. If there is knock again, it will again instantly go back to the 95 RON mode.

The ECU can not automatically advance timing beyond what it is mapped for. It can only retard it in case of knock.

Why is it better to map it to 95 ron? Surely the ecu with knock control can be mapped on 98-102 ron and the ecu should still adapt down to compensate for the lower grade 95 ron usage, otherwise it seems to me the knock control is not doing its job.

If you are always driving on 95 RON, then you should map it on 95 RON, because otherwise you are just stressing the engine more, especially with higher performance on stock components. You just increase wear on the engine.

If you are driving usually on 98 RON, but have to sometimes fill up 95 RON, because there is nothing better, then it is okay to drive the car as always, knock control will protect the engine.
It still increases wear, but to a negligible amount.

For race gas you should have switchable maps, because race gas allows you to run MUCH more timing than normally, and if you try to run that timing on 95 RON you will rather quickly damage your engine.

Knock control is mainly designed to work from say 99 to 92 RON, or even 98 vs 95.
It is not designed to work from 110 RON race fuel down to 95 RON.
That is why your car manual says the minimum acceptable octane level is 95 RON.

[bernsaudi]

I am aware of the first part of what you say Jamo, my question is when the car is mapped at 98 ron and it has 95 ron in should the knock control deal ok with it if the vehicle is given full throttle? Am I not right in thinking that is what it's there for, adjusting to deal with the parameter of the engine given a set of conditions so as to not let the engine get into trouble?

I live in an area that has no 98 ron and so the car generally gets 95. The turbo itself is good for 380+ hp, the injectors in this instance are 360cc I believe and the ecu will push to 1.9 bar in the top gears, it has a wagner em on. I dont know what power the engine is developing but the car goes respectably without problem on local fuel however when I put something better in it really flies! I had this setup for 18 months and recently had a 3 inch downpipe added.

Am I right in thinking that this (motronic)ecu will lower boost when offered lower grade fuel or does the boost remain the same and the timing retard according to the current knock situation (as well as other things). What is the difference in the behaviour of an ecu that has knock control disabled compared to one which has not from the point of view of the driver?

[Jamo]

Not in the way you are thinking no basically you are asking the ecu to full time reduce its ignition map through a fault condition
It's like a woman taking the morning after pill instead of using birth control

[UrS4boy]

G61 and G66 Knock Sensor info

If one of our cars has been mapped whilst running 98 octane fuel and then ends up on 95 octane fuel will it run without problems until better fuel is found. Can the ecu cope with the poor grade fuel?

This G61 and G66 Knock Sensor info post might help the discussion:

http://forums.quattroworld.com/s4s6/msgs/21047.phtml

[prj]

I am aware of the first part of what you say Jamo, my question is when the car is mapped at 98 ron and it has 95 ron in should the knock control deal ok with it if the vehicle is given full throttle? Am I not right in thinking that is what it's there for, adjusting to deal with the parameter of the engine given a set of conditions so as to not let the engine get into trouble?

I live in an area that has no 98 ron and so the car generally gets 95. The turbo itself is good for 380+ hp, the injectors in this instance are 360cc I believe and the ecu will push to 1.9 bar in the top gears, it has a wagner em on. I dont know what power the engine is developing but the car goes respectably without problem on local fuel however when I put something better in it really flies! I had this setup for 18 months and recently had a 3 inch downpipe added.

Am I right in thinking that this (motronic)ecu will lower boost when offered lower grade fuel or does the boost remain the same and the timing retard according to the current knock situation (as well as other things). What is the difference in the behaviour of an ecu that has knock control disabled compared to one which has not from the point of view of the driver?

Jamo already said it in laymans terms.
But basically for the ECU to CONTROL knock, knock has to HAPPEN beforehand.
So if you are running it on 95 RON, yes, ECU will save your engine from the worst, but it will still be knocking every now and then. How else could it react to 95 RON fuel?

Get a set of detcans and listen to your engine.
But yeah, if you are running the map I think you are running, knock control is pretty much non-existant there. All threshold maps just lifted up. So you are likely stressing your engine a lot by putting 95 in.

[bernsaudi]

Thanks for that URS4boy...that is what I needed to see.



The timing is dynamically retarded when knock is detected by 3 degree segments until noise is diminished, if knock continues the mixture is richened up to bring down chamber temperature and if the knock continues the charge pressure is reduced, this is what I thought happened. This allows our cars to be able to run on 98 ron fuel and when it has lower grade fuel continue to have the throttle pressed fully down by a driver with the knowledge that the ecu will reign in the timing fuelling and boost pressure in that order before any damage is done to the engine.

[prj]

Yup, but there is a difference between having the car at 380hp and stock.
Also, if in the ecu the knock thresholds are lifted very high, then knock control is effectively disabled.