The MPGuino needs an injector "signal" from the injector's ground wire.
Reason is, the positive wire is always hot and the ground is switched by the computer to control injector pulses.
On my '97 Civic I hooked mine up at one of the injectors. Doesn't matter which one. Check for voltage in the two injector wires with ign switch in "run" position, and use the wire that has no voltage. That's the switched ground. Yes you also could find that wire at the computer harness but I was more comfortable tapping into it at the injector.
Good luck with it - super project! Project thread, in case you haven't stumbled on it:
http://ecomodder.com/forum/showthrea...crx-17565.html