Pushing the pedal did three things:
- it “primed” the engine by using the accelerator pump to spray some fuel in
- it set the automatic choke
- it set the idle to high, via the high idle cam.
Fuel injected systems control the engine’s starting fuel needs by computer.
Eraser gave an excellent description of a majot difference, being that pumping the pedak before turning the key does nothing on a fuel injected car but open and close the throttle plate. The computer in an injected car takes a signal from the engine temp sensor, and based on that combined with the other sensor inputs it
- richens the mix (makes the injector pulsewidths longer) and
- by passes the oxygen sensor circuit, to allow the engine to run rich,
In short, in a carburated engine everything is operated manually by linkages. Pumping the pedal sprays gas into the engine and sets the chok & idle for cold operation.
In an injected engine, all of its fuel comes from the injectors. The injectors stay closed when static and only open when a signal tells them to. Thus, when the kay is “OFF”, there’s no signal, the injectors don;t open, and nothing happens.