Before I attempt to tune my ignition timing I want to make sure I have an understanding of how the various tables are used. I have read all I can find on this forum, Hondata and the Flashpro help file but I still have a question about the knock limit table. Here is my list of assumptions and question

If I understand correctly, the knock limit table values are offsets from the values contained in the MBT table (ignition high/low tables in Flashpro).

A positive knock limit value denotes the amount of additional advance over and above the best power setting (MBT) that can be applied before knock will occur.

A negative value tells the ECM that the MBT timing cannot be achieved without knock so timing is "retarded" from the MBT value but will not show as knock retard because this is a known condition irrespective of fuel quality (because we can't get very high octane fuel from the pump like they use to develop the MBT value)

The Flashpro help file states: "...the ECU will use the lower of the MBT timing and knock ignition limit so that the engine will make the most possible power, but will not knock."

With this being the case I am having a hard time understanding how it ever uses a positive value from the knock limit table since it always uses the lowest value between the MBT and knock limit tables. The only thing I can think of is that it uses the positive values as it transitions load columns to moderate any large timing jumps between columns. Otherwise it seems that I could set all the positive values in the knock limit table to zero with no change in performance.

Somebody please help me understand. Thanks

 

Crickets...

 

*brain explodes*

 

I could be wrong but from what I understand, the commanded IGN is the value of Knock Ignition Limit - (K.Control * the Knock Retard table) or MBT, whichever is lower. If your ECU thinks it's detecting knock and therefore raises the K.Control value, it's possible for the former to be lower than MBT, even if the KIL is positive vs MBT in the table. I am not an expert, but this is what I understood from the FlashPro help files.

 

Here is what I have experienced so far.

If the value in the KIL table is negative the ECM will retard the timing by that value from MBT unconditionally.

If the value in the KIL table is zero or positive it provides a buffer that is added to MBT then used as a starting point before it actually retards from MBT.

So for example, if MBT is 24 and the corresponding KIL table value is 4 and the result of the knock sensor noise/k.control/knock retard calculation results in a value of <= 4 then the timing will be set to MBT/24 (no higher) BUT if the result of the knock sensor noise/k.control/knock retard calculation is >4 like say 6 then timing will be set to 24+4-6=22 for an effective retard of 2 degrees. Clear as mudddd. What a simple system...

My car will never see octane greater than 93 so at this point I have yet to understand why I need a value in the KIL table greater than zero. I think I should be able to relax the knock sensor noise limit just enough so it doesnt retard timing all while making sure there are no knock counts. My k.control is currently running consistently at 55% so if I do get some bad gas it should still increase k.control and the amount of ignition retard to protect the engine.

 

That was exactly my experience as well and lines up exactly to my explanation of the system. I've also noticed K.Control always seems to run no lower than 55%, which I don't understand. According to Hondata, a value of zero corresponds to 100 RON (95 AKI in the US) and 100% is 90 RON (or 85 AKI). Always being at no less than 55% would mean the ECU never expects greater than midgrade gasoline basically (89.5 AKI = 55% K.Control), which makes no sense. I spent a lot of time figuring out this crazy system due to cyl 2 phantom knock issues. Hate hate hate argh

 

Also, I forgot to mention, the values in the knock retard tables are linked to the values in the knock ignition limit tables. If you have a positive KIL value, you don't want to zero it out, because when K.Control DOES want to apply knock retard (when KIL - [knock retard * knock control] is less than MBT), you'll get more retard than needed at that index. It's probably better to leave it at the value it is (unless you want to adjust both the KIL and the Knock Retard at the same index). The system definitely seems retarded from our point of view, but I think it's designed the way it is because of varying motors from factory and fuel quality from region to region. Not a tuner's concern, but most definitely Honda's concern.