Electronic fuel injection for spark ignited/petrol road vehicle engines uses a feedback loop, ie. a voltage from an oxygen sensor in the exhaust system is fed back to the electronic controller.
The more oxygen in the exhaust (= a lean mixture, not enough fuel put in) the higher the voltage produced by the sensor and the controller holds open the electronic injector(s) for longer to bring the mixture back to where it's required.
Unfortunately the oxygen sensor cannot tolerate leaded fuel (lead salts from combustion contaminate and "kill" it). So this type of system can't be used on an AVGAS burning engine and the pilot needs to get more involved in setting the mixture for himself.
AVGAS still contains a lot of tetraethyl lead, despite the "LL" designation. It's only low lead compared to what it used to contain. To put this in perspective, it contains about five times the lead content of "old fashioned 4 Star" petrol. For racing purposes only, of course, one gallon of AVGAS in a five gallon tank of cheap pump unleaded gives you a similar octane rating to that of 4 Star. AVGAS must not be put in a modern catalytic convertor equipped engine because it will also ruin that, as well as the O2 sensor.