90 Grand Wagoneer - chasing cold start hesitation/rough idle

[dave w]

Every project ultimately has to reach a decision; is good enough, really good enough or is there something better?

The ICM cannot be programmed to optimize the timing (Spark Advance).

See sample 1227747 timing table below. The 1227747 controls the Spark Advance via the ignition control module. 1227747 timing tables use a metric vacuum scale call Kilo-pascals (Kpa). WOT Kpa is 100 (kind of like- nearly Zero Hg), and coasting down a 3 mile long 10% grade is 10 Kpa (kind of like nearly 20 Hg). Cruising on a level grade at 70 MPH is usually between 50 Kpa to 70 Kpa.

Better just might be the ability to optimize the timing (Spark Advance) at WOT, Cruise, and Idle?

GM Ignition Module / ECM schematics are also attached below.

dave w