Marcel, it will be straightforward to add a gear indicator as you mentioned; it is reported by the ECM as part of the runtime dataset. Information on runtime data:
http://ecmspy.com/cgi-bin/runtime.cgi. I would like to add navigation as well, but due to apparent limitations in the Google Navigation/Maps Android app, it is a lot more work than I want to take on for now.
Sirius, I agree that there are better options for power supplies- I'll be looking around before I make any purchases and haven't ruled out just building something myself. I'm concerned about transient voltages destroying my project, but even more so about power system noise causing random bugs- there is nothing more frustrating than poring over code for hours, only to find a bad ground or some power issue to be the problem. As far as power output goes you're right, the Arduino will max at about 10W, and the displays power use will be minimal. I figure a little extra clean power for expansion isn't a bad thing though
I know the right pile of mosfets, capacitors, and diodes would be easy to solder up, but I'm no engineer so Ill probably leave this part to the professionals. If you have any suggestions or expertise- I would appreciate the help!
AZmidget, this guy did some datalogging and hp/torque estimates for a class project:
http://arduinobuell.blogspot.com/, and Ive seen another similar project someone did including a display hacked into the stock gauges, but I cant find a link now. Once communication is up and running between the arduino and ecm, it will be straightforward to run all of the tests that ECM spy can do - coils, injectors, fuel pump, tps, etc.. I know I'm not doing anything really new, just doing it the way I want to
I had an idea this morning that I thought a few folks could find useful: It wouldn't be all that difficult to load custom maps to an SD card and set up the arduino to reflash the ECM on command.. You could have a map for the track, a map for commuting, and a map for those damn 8,000ft peaks just West of here..
Thanks for the feedback everyone!