Make no mistake, the AYBK is a very different calibration than AUAH. AUAH was the second release production calibration circa 1989. AYBK was released nearly 4 years later and, like all the service cals, is substantially different. Mind you, I am not suggesting its better, or even noticeable, but it is different. Here are some of the changes:
- change to Hot Restart spark retard
- slight changes to low-load / idle spark advance
- less MAT-based spark retard
- new idle speed spark corrections (added correction for low idle speed)
- more DFCO spark retard
- tweaks to startup spark advance (and decay) values
- ESC knock retard entry thresholds reduced
- Added low octane spark retard logic
- some new canister purge / integrator reset values
- CARS (CAGS) barometric pressure criteria added
- shift light disabled via temp threshold
- Baro pressure read/update logic added. And a host of BARO checks to various functions in the program
- minor tweak to crank fuel pulse width
- less open loop MAP enrichment
- various startup enrichment parameters changed
- added new startup enrichment vs. MAT
- Totally re-written / new Closed Loop fueling logic
- warm restart fueling adjustment added
- DFCO enable tps v. RPM added
- vastly different Accel Enrich strategy (was TPS-based, now both TPS & MAP-based)
- speed-based throttle follower offset added
- various tweaks to better control IAC
- new IAC keep alive memory function added
- new IAC control added when in DFCO
- new fuel trim factor vs. Baro pressure added
- slight fuel table (VE) changes
Whew! That about does it. It (along with the other "service" issue calibrations) are just simply a little more refined, complicated than the original issue ones. Not saying its better or worse. Engineers tweak anything when given enough time, and over 4 years they just got more sophisticated in the LT5 calibration approach.
Hope this helps.
Todd