Bought one of these for the heck of it. I found one in the close out aisle at Sears but it is older and doesn't speak CAN bus which the Jeep seems to use. It seemed interesting so I bought a USB model. The USB model (8221) works fine with CAN bus cars. The E/X model will record speed plus 4 of 23 available parameters at 5 second intervals. Most of the parameters only apply to gas engines. Useful stuff I can get are RPM, manifold pressure, intake temperature, engine temperature and a few others. You can't see the data real time, you have to download it to your computer.
So far I know that I've peaked man. press. at 32.5 PSI. Looking for a boost gauge? Get one that goes to 35PSI.
My engine temp has never gotten over 175F.
Intake temp has gotten to 167F and cools slowly when in cruise to about 100F.
Boost at cruise speed varies between 17 and 25 PSI.
It gives you a graphs of the data. I have proof that the transmission doesn't shift into top gear unless I speed up to 65 then slow down to legal speed.
Can someone with a repair manual look up something for me. What temperature does the computer need to see in order to switch out of warm-up mode? My older gas truck had a thermostat stuck open. The engine never got to operating temp and the computer kept the fuel system in warm-up mode causing the mileage to be bad. I have never gotten over 20MPG in my Jeep. If it thinks the engine is cold, that may be the reason. I know the diesel is not the same as a gas engine but computer operating logic is generally the same.
Read about the Carchip here
http://www.davisnet.com/drive/index.asp