Bit B3 has been assigned to indicate Petrol or Diesel in the 2007 version of the spec.
Wikipedia here has the latest/newest/correct information.
Get a copy of Sae J1979 and all your questions will be answered.
The information from obddiagnostics is out of date by something like 15 years or more.
Pid 1F and following have been around for a long time now.