View Full Version : Knock parameter on scanmaster3 for wrx

11-06-2009, 11:17 PM
I have had the scanmaster3 in my car for a few
years now and really like it!

One thing that has bothered me about the scanmaster is the knock value that is shown on the main screen.

It appears to be the 'knock correction advance' parameter reported by the ecu. So it shows the amount of timing advance added to the base timing map.

You can figure out if there is knock, if you know what the values are in the max ignition advance map.

Would it be possible with a firmware update to make the main screen's knock
display show the 'feedback knock correction' parameter from the ecu?

I think that would be a much more useful value to display.

The displayed value would be 0 unless the ecu is pulling timing due to a knock
event and in that case it would show a negative value (how much timing is being

11-07-2009, 12:23 AM
I haven't looked at that software in years...... When we developed the SCM3 for the Subaru that knock parameter was the popular one to use.

I'm not sure I have the details on the knock feedback. Do you know the address of that parameter?

The GM stuff has a similar parameter, "Knock Retard", its generally shown as positive degrees, and you tune to minimize it. By not using a negative sign, you save one digit in the display as well.


11-07-2009, 03:40 AM
I can understand how that would be a popular parameter to display.
But its really difficult to tell if there is lighter knock (few degrees of retard) since the value constantly changes very quickly based on rpm/load minus any learned correction at that rpm/load point plus any feedback correction(negative value).

It would be awesome if it could the display the feedback parameter, acting more like a knock light. Any value other than 0 would indicate that the ecu is hearing knock from the sensor. And how far negative that value is would show how severe the knock is at that moment.
It would be even better if it could flash the value on and off anytime its not 0 to help draw attention to it...I am probably dreaming :)

My ecu ID is 1B14400605
and the address for the feedback knock correction is 0x20B80

What I can tell from logging, it increments -2.11 degrees (funky ecu math?) each time it hears a knock event, then slowly(every second or 2) adds the timing back 1.05 degrees at a time, as long as it doesn't hear knock anymore.
I wouldnt mind if it was displayed as a positive number, although I don't think I would need the extra resolution gained by removing the minus sign, since the ones place is the important part.

Thanks for your help!

11-07-2009, 04:52 AM
I think I can make something work.

Are you running software version 1.1 in your scanmaster?

I assume you have a laptop handy to reprogram the scanmaster.

It will most likely take a couple tries to get it right. I'm somewhat buried with some other projects, but can take a couple whacks at it.


11-07-2009, 06:54 PM
Yes on the 1.1 and the laptop.
Whenever you have time.