Where to start for ODB/MPGuino?
 

I have two vehicles a 2007 Jeep Liberty and a 2003 Saturn ION. I would like to build a device/gauge that can keep track of the MPG and diagnostic codes on both vehicles. I know the ION uses CAN protocol, the Jeep, I have no idea. I would be nice to have data logging too, to a USB flash drive or SD card. Is this possible? Are there construction guides? Kits? I am new to microcontrollers, LCD displays and such so any input and help will be much appreciated.

I would think your best bet would be something like the scanguage. This forum and the MPGuino mainly focus on pre-'96 cars that have no other options.

The scanguage seems like it should work with both of your vehicles (but if your Liberty is the diesel version [did not know they made one] then it should still work, but some of the guages/displays might not work).

You can read about what it can do here:

ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool

The Jeep should be using the CAN protocol as well. My 07 RAM does, and so does my wife's 08 Avenger. I think Magister tested his OBDuino with a Jeep and it did not like it, so I don't recommend that.
There are several devices to consider that support CAN:

Auterra's palmOS package Dyno-Scan for Palm CAN
PLX gauges PLX Devices : Moe’s Performance, offering Dodge, Chrysler and Jeep Performance Auto Parts, HEMI Performance Parts
Dashhawk DashHawk Vehicle Information Display
Nology PDA Dyno PDA-Dyno and OBD2 Scan Tool
Aeroforce Interceptor Aeroforce Technology Inc | Products - Interceptor
AutoEnginuity scan tool Products
Scantool LLC ScanTool.net LLC - Scan Tools, PC-based OBD-II (OBD2) Interfaces, OBD diagnostic software
OBDKey OBDKey. OBD Bluetooth and OBD USB Products.
OBDPros OBDPros software link on the page
BlueOBD (a DIY type thing) blueOBD - bluetooth project based on OBD-2
[edit] OBDGauge software http://www.qcontinuum.org/obdgauge/

Yes, I have been looking for a while. :) Auterra, Dashhawk, Aeroforce and PLX log data, and maybe the Nology and AutoEnginuity as well. Hope this helps.