On the OBD 1 and 2 questions. HD vehicles (over 8600lbs) run OBDI software in an OBDII pkg. OBDI will not register misfires, catalytic converter failures (no downstream O2 sensors), and some don't have EGR.
My Excursion is an 02 and has OBDI software in an OBDII pkg. yes it will still have an OBDII connector but the system doesn't have the software to monitor other systems. And yes OBDII scanners will read, it will just show up with certain monitors that have not passed (and never will), and some data pids that don't exist in the software.
