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I followed aaron cakes guide and base maps for my 1987 Rx7 TII. I have a question regarding the ignition table. This is on my megasquirt ms3x.
What is the purpose of the low advance area at the 700-800 rpm range, mainly the 5.0s. Should these be there? I have some tip in problems that occur in that area, and im trying to determine if its an acceleration enrichment problem or a problem with the ignition table.
The flame front moves quickly compared to the speed of the rotor at low speed, so it's not necessary to fire the coils as early. Similarly, at high load (near 100kPa or above) the flame front moves more quickly than at light load (50 kPa or below). Those cells are both low speed and high load, so that should be the lowest ignition advance needed. Without a supercharger, the engine will never reach the low RPM boosted cells (125kPa and 0-2000 RPM), so those numbers don't really matter. If the engine could somehow reach those cells they would need to be lower numbers.
Remember to use a timing light to check if the ECU's timing numbers match what is actually happening at the crank (eccentric) pulley. If your map shows 10 degrees but the coils are actually firing at 15 degrees, that needs to be addressed before running the engine hard.
For a bit more safety margin, I would change the 100kPa cells to 20 degrees and all of the 125 kPa cells to 10 degrees. Then add a few degrees more timing on the dyno and only keep it if the extra timing gives a significant power gain.
I doubt the engine needs 245 degrees advance at 1200 RPM either, but that's relatively light load so there's not much harm in keeping those numbers and seeing how it runs.
Last edited by scotty305; May 29, 2023 at 04:45 PM.
If I'm guessing, that map was probably adapted from one made for an earlier Megasquirt which may not have had a separate setting for cranking advance. This won't affect running operation since you will never be at 100% load and 500rpm and it won't hit those bins. I don't know this to be true, but it makes sense.
MS3X (and probably Microsquirt as well, if not MS2) has a setting specifically for advance while cranking which overrides the table.
