I was going through this DIY section and found in the thread DIY homemade MPG monitor. In this thread some of the folks there are making some componets (Connectors) downloading a program(some are free),and using a sound card from their PC(personal Computer) to monitor what is going on in real time with their vehicle. They are basically monitoring the ALDL(Assembly Line Data Link) using the OBD( on board diagnostic) system. (This is how I understand it)
I was totally lost. I found a site that has some great info and some links to free program software and some that you can buy. They do a great job explaining how it works. I have not read everything on the site and do not understand how it all works.
Here is the site.http://http://www.aldlcable.com/
Maybe some of the folks who have made the system can explain it better.
I have a vehicle that has OBD I and its hard to find cheap scanners that give you this kind of data.