Only the pre-90 ECMs supported 160 baud. In 1990 with the introduction of the CCM, they all moved to 8192 baud (and went from Pin E on the ALDL connector to Pin M for good measure).
Also, figured out the weirdness with your poll. Your poll does make sense since the checksum is different. But both my documentation and an idle scan from a guy on Corvette Forums show the idle poll to be 40 55 6B instead. However, my documentation is from 1989 when the CCM was first introduced, and that user had a 1990 Corvette.
I went back and looked at a log that steveo had me take of idle traffic on one of my cars, and got 40 57 FF FF 6B as my CCM poll. I'm not sure which of my two cars this was since I didn't make a note of it.
I did however take other logs that were marked. My '94 showed the following polls:
94 Key Off: 40570C025B
94 Key On Engine Off: 4057FFFF6B
94 Key On Engine On: 4057FFFF6B
All very interesting. It would appear GM added two bits at some point after 1990. I wonder what the difference in poll is between key off and key on?
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