Once more - Ignition Max tables

[mrQQ]

ok,

so I can't figure for my life - why did Mazda set Max tables lower than normal tables in certain (low load) regions?

What's the idea here?

[mituc]

I guess that's only for really low load situations, close to engine braking, just to ensure the timing goes to the max as fast as possible. I guess it's something related to emissions.

[mrQQ]

still doesn't explain why they wouldnt just set normal tables high, and max tables the same. Why reverse them?

[mituc]

The actual advance timing depends on a lot of factors, but in this case the most relevant are the boosted air temperature and engine coolant temperature.
if you have a target value in a normal timing table the ECU will not immediately use that in certain conditions. When the target is set higher than the max (meaning, much higher in this case) the timing adjustment/compensation premises are not met and the value will go directly to the value in the MAX table (which is lower).

If, say, in a certain situation the actual timing value that needs to be used would be the "table value" - "compensation value for the ECT" - "the compensation value for the BAT", instead of, say, 50 degrees you will end up with, say, 42 (it's just an example).
If the table value is set to 60 and the corresponding value in the max table is set to 50 then the actual value will be like:
"table value" - "compensation value for the ECT" - "the compensation value for the BAT", so 60 - 8 = 52 which is greater than the max, so the max value of 50 will be used instead.

So in the second situation you will end up using 50 degrees right away without waiting for the car to move and ventilate (which will make the compensation values to be smaller or 0 when you can finally use 50 degrees).

[mrQQ]

ok, so this makes sense. It's like using max table as a "ok, in this area, don't do any kind of compensation at all" way.

however, I'm still not sure if that's what mazda meant. The area where max is lower than normal table is 1000..3500 and up to 0.5 load or so. This is either a cruising range, so they wanted to optimize MPG, or a range where you're most likely to smash the accelerator and need a quick spoolup.

I guess I'm worried, that there is some logic built into ECU, which says, if max is lower than normal, do something else. Perhaps Steve can chime in?