OK, we've got these three timing tables.

[HRD]

Who has made the main, idle base, and coastdown spark tables all the same? I've had issues with jumping between timing tables at low speed causing a surge since the timing is quite different between the tables. From what I've read this seems to be a common occurance.
The question that noone seems to be able to answer is what determines which table is being referenced and how to change that. Some have had luck with bringing the values of the tables closer to each other to reduce the amount of timing change when the ECU jumps between tables. I've use other aftermarket systems with only one main timing table that work just fine. You just adjust the timing values for idle and coastdown at the load/speed that the engine idles or coasts down at. Why not do that here? I mean do we really need completely seperate tables for idle and coastdown?

[IDRIVEAG8GT]

Each table should be set completely different. You especially need more timing in the main spark tables versus the idle cells to prevent this issue that way the car won't surge and your idle spark overspeed/underspeed tables work correctly.

[HRD]

Each table should be set completely different. You especially need more timing in the main spark tables versus the idle cells to prevent this issue that way the car won't surge and your idle spark overspeed/underspeed tables work correctly.

OK, I realize that you need less timing at idle for these reasons, but why not just adjust those cells in the table that the engine runs at when idling rather than a whole different table?

[DSteck]

Because you can have loads when you're trying to take off from a stop, and if you're only running enough timing to idle, it won't have torque to move. If your coastdown spark is too high, the engine may not slow down.

[HRD]

Well for example, what I'm looking at is my engine idles at around .23-.26 g/cyl airmass at 950rpm. As soon as I touch the throttle, the airmass jumps up to .40 or more, so why not just set the timing cells at .28 g/cyl or less to the desired idle timing value and quicly ramp up above that airmass? Likewise, on coastdown, the airmass is less than it is at cruise. So why not just lower those values in the timing table that are referenced during the coastdown and leave the values at the higher airmass cells at the higher timing?

[DSteck]

Try it and find out.

[HRD]

OK.
Do you know exactly what conditions cause the switch between the tables?

[kyphur]

If your coastdown spark is too high, the engine may not slow down.

Just a quick question but is the coastdown spark you speak of the "idle adaptive spark control overspeed"?

[DSteck]

No. Coastdown has its own table.

[kyphur]

Ah, o.k. Don't have that in my setup apparently.

[HRD]

The Coastdown table is under "Idle Spark Advance".
Well I seem to have accidentally fixed the timing fluctuation by calibrating the speedo.
I was going to make a baseline datalog with the timing jumping and surging and then make changes to the timing tables as discussed above. But first, I calibrated the speedometer reading in the VCM using GPS. It was reading way lower speed than actual. After calibrating the speed, the timing is no longer jumping fluctuating like it was before under the same load/actual speed. I still feel a very light surge, but it is much better than before and the timing was very steady when the light surge was felt. I think most of the remaining surge is just due to the cam/large plenum intake.
This indicates to me that the vehicle speed plays a large part into which timing table is being referenced.

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Can you adjust coastdown timing to get better mileage? If not I am trying to get better mileage does anybody know how.