I noticed you applied a very high tech test resulting in the engine starting, Why not start with thoroughly checking out the condition of your battery, battery cables, and making absolutely positively certain you have a good ground. This infers a good ground between the battery and the frame and the frame to the engine. I highly recommend doing this before doing anything else. Maybe you should buy a new high quality battery such as an Interstate or an equivalent. Also tell us a little bit about the condition and maintenance of your xfire.