Originally Posted by
RobertISaar
OLDPA3 (decoded: previous pulse accumulator #3) = knock counter.
and you can always use just the LSB of the spark advance, it's a signed(or is it 2's compliment?) value, so unless you get near firing ATDC often, i wouldn't think its an issue. when bit 7 of the MSB is set, then the SA is displayed in ATDC, with FFFF being 0* or 0.39* ATDC and lower numbers being even further after TDC.
and yeah, once you have control of the datastream, you'll wonder why GM put in some of the stuff that they did.