Just did another timing test with the same scan tool in my chevy silverado, it has a 5.3L v8.
this engine idles at 17-18 degrees positive timing. And under WOT it advances to about 32 to 38 degrees positive timing.
and when I get off the gas it will advbance up to 50 degrees positive timing then slowly come down to 17 degrees again at no load.

any thoughts on this? I'm thouroughly confused. is there anychance the scan tool is reading the crossfires' timing out of phase? which is why I get negative numbers?

I'm using the INNOVA ScanTool CANOBD2 1303