If the voltage drops below about 8.5v when starting, the Mk1 will reboot as the 3.3v rail goes out of regulation. A diode and a capacitor (which doesn't really have to be a huge thing - without doing the calculations, maybe a couple of 4700uF 25v ones might do it) could help, depending on how long you have to crank your engine for.

The Mk2 is a bit better, as the new PSU will keep the CPU running down to about 5.5v. The Mk1 would reboot when I started my CRX, the Mk2 would blank the display (powerfail) then come back without a reboot every time.

Hugo