Hi,

Just wondering if the knock count (e.g. 3, 7) acquired through logging has a specific unit of measurement?

I imagine that the sensor will be reading something like frequency and reporting that raw (and measured) value back to the ECU.

Does the ECU then return the value from the sensor in its raw form, or does it process it into an arbitrary value before returning through logging?

Thanks,
Brendan

 

I suspect the sensor measures voltage and that value is cross referenced in a table and then is used by the ECU to retard timing. I think it's likely that the ECU correlates more knock counts to a higher voltage value from the knock sensor. However it could work the other way, the knock sensor could only have 1 signal type and the ECU might just poll it many times per second and the knock counts are cumulative, or both!

One thing that I do know is that the ECU will pull 1 degree of timing for every 3 counts of knock that are detected by the sensor.

 

Thanks - I understand how the knock count works within the Evo ECU, I just specifically need to know if the value that is returned through logging (i.e. MitsuLogger) has a unit of measurement, or if it is an arbitrary value.

When I say "unit of measurement" I mean something like counts per ms, or Hz, or V or similar.

By "arbitrary value" I mean a number that has no unit of measurement. On it's own it is just a number, but when taken into context of scale (e.g comparing 2 to 17) it has value and meaning.

So - does anyone know if the knock count has a unit of measurement?!

 

AFAIK, the knock sensor only returns a voltage. The voltage varies depending on the strength and pitch of the frequencies that are being picked up from the block. The resulting voltage is then used by the ECU to determine a knock count value.

l8r)

 

Most OEM ECU's use the knock sensor voltage and a threshold value, which changes with engine load and RPM(the knock threshold is usually lower at higher engine speeds and high engine loads...a lower threshold means more sensitivity to hear knock). The ECU uses this predetermined knock threshold as a calculation of knock. Once the voltage surpasses the threshold, the ECU considers the event to be knock and counts off one knock count. At this time, the ECU retards ignition timing according to it's knock protocols, usually 2 degs at a time until knock is no longer heard, then advancing back to the original timing for the given table, until knock is heard again(by knock voltage exeeding knock threshold), and the process starts over. Every time this happens, the knock count rises.

CJ