Understanding Spark - $42 7747

[shimniok]

I want to continue to try to wrap my head around spark advance in the 7747 $42 mask that I have. I've seen some of EagleMark's posts (this and this) that describe it, and have looked thru the latest XDF's comments. I am putting together a spreadsheet to (try to) duplicate the interaction between tables and parameters. I'm using ASDU

Let's assume temp of 185-195°F so I don't have to deal with Coolant Comp Spark Adv yet. Let's assume cruise and no PE, DFCO, or AE involved. Let's assume there's no knock retard happening. And let's talk about 400-3600 rpm only for the moment.

Starting with the Main Spark Advance table, it gives the ECM a mapping between spark given rpm and MAP. So the ECM knows what rpm and MAP it's at, and it can interpolate given the table, what spark to start with.

Then it subtracts from that the Spark Bias-Warm value (9.84).

Then it subtracts the Initial SA (0 in the stock bin) (EDITED 9/21)

Then it adds the unbiased value for Coolant Comp Spark Adv. It gets that unbiased value by subtracting Spark Bias-Cold value (20.04) from whatever the value is in the table given MAP and Temp. Let's say the temp is 195 and MAP is 30. The entry in the stock bin is (gasp) 20.04. Subtract bias. You get 0 spark compensation.

So if you were to take the Main SA table, subtract Spark Bias-Warm, subtract (edit 9/21) Initial SA, then subtract the actual base timing (let's say your dist is set to 0), add in the applicable Coolant Comp Spark Adv, subtract the Spark Bias-Cold, then you'd get the almost actual spark advance? Except HiWay Spark Added (stock bin is zero'ed out).

...and ... except for Spark Latency Correction-- how does the ECM use that? (I'll go search)

What else comes into play for this simple case? I'll ask about other specific cases later.

In terms of practical application, I'm not doing anything with SA tables for awhile. Hoping it is "close enough" However, I do need to set my Initial SA scalar to 10 to match my distributor base timing which we set at 10. I've been running around with Initial set to 0 without knowing it until last night. Before I do more test and tune I need to fix that.