Efi is electronic fuel injection,delivers precice amounts of fuel at correct intervals for combustion,Ecu or electronic/engine control unit (not sure which) ,controls and monitors this and many other components/functions

Yep. spot on above. Car computer systems are now very advanced, they allow the sort of fuel economy and power you see from a modern engine coupled with the advances in manufacturing and material technology. 40 years ago a 2 litre 4 cylinder ma55 produced petrol engine might have made 90 horsepower and done 25 miles to the gallon in a saloon, Now they would typically have at least 130bhp and do 35 to the gallon as well as a hundred times cleaner exhaust emissions.

This just wouldn't be possible without precise electronics controlling the engine- spark, timing, fuel injection, emission feedback etc it is especially crucial for emissions, the lambda sensor means the catalyst works to a high efficiency.