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MGV101

Some confusion with onboard knock control

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Looking at the help file on PC link, it appears knock control uses two systems to retard ignition as a result of knock. The description in the help file isn't particularly clear but it seems like on an global level, when knock is detected, it will retard ignition timing according to how much the threshold had been exceed and the retard gain. Any subsequent knock will continue to increase such retard and the retard will be gradually advanced if no further knock event occurs. It appears to me that this ignition retard system is carried out on a global level regardless of RPM and load am I correct?

In addition to the global system, when a knock event occurs, a value will be subtracted into the cyl X ignition trim table which will retard timing at a specific spot. Looks like this retard is permanent and will not be advances until it is reset (ie. when ECU powered on) and any more subsequent knock at the same spot would add in more retard in the table.

If the engine had been knocking and we happen to be running into a spot where there is a retard value in the cyl X ignition trim table, will both the advances be added up? Also about the maximum retard value, does it apply just the overal timing or is it separately applied to the "global" retard and the cyl I trim?

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Only trims will be the cylinder ones if you have set it to trim cylinders individually. However if you only have one trim table and all cylinders assigned to it then it would operate as a global trim.

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Thank you Simon. If this this the case how does the timing gets reintroduced back into the system?

Seems like when no knock occurs for a specific time, the ECU will try to add timing back. When this happens does it simply add timing back into whichever i-trim cell the engine is currently operating at? Or does the engine have to stay in a cell for the delay countdown to activate and add back timing to that specific cell?

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The engine will need to be operating in the specific i-trim cell, with no knock detected for the set delay period, before that specific cell (only that cell) will start to get re-advanced.  There is also the "clear I-trim table" setting that will remove all retard trims at every power-up.

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