Timing Table Help for Bucking

[SRS_Chris]

Working with a 525hp LS3 crate engine from GM. This has the "ASA" GM camshaft. OS is from a Gen3 1999 Corvette. After lots of learning (and criticism) I have the engine running and idling pretty good. The car will start, idle, and run at WOT without issue. The car will also drive & cruise above 1,800 rpm without any noticeable issue. All testing thus far has been performed in OL.

Here's where the fun starts...

Off idle tip in (accelerating lightly from a stop) and decel at low rpm (below 1,600 or so) will produce bucking/trailer hitching. I have tried adjusting the VE table (helped a bit a first, then hit a wall). Tried commanding various AFR's (richer and leaner) after VE tables were adjusted with no help. I have discovered that increased timing upon acceleration will eliminate bucking, as will decreasing timing upon deceleration. The problem is that the ECU uses the same cells (as far as I can tell) for acceleration, idle, and deceleration. I have tried using the HO/LO spark tables and idle tables with the hi/lo spark values and adjusting the "TUMBLE FLAP CLOSED" values (used to determine if idle or HO/LO tables are used), but I can't make it work (high spark upon acceleration, low spark upon deceleration, medium spark for idle).

Anyone know how to accomplish this?

[dermotw]

As far as I know, by doing just what you're doing... repeatedly... I have done it (tweak, test, tweak again...) dozens and dozens of times to get rid of it <all> and still there's a bit left..

[kingtal0n]

Your timing table probably is not smooth enough, Use HPtuner to show the decimal values. Alot of times you have a row like this:

15 15 15 15 15

but really its like this

15.243 15.484 15.313 15.195 15.934

see as the engine tries to acclerate the timing is erratic, the engine doesn't know if its coming or going. So make it smooth like this

15.141 15.249 15.3458 15.4584 15.565 15.674 make sure the decimals are increasing slightly as you go to the right from left, and up from down