Modern gasoline engines use what system to deliver fuel into the engine?

Fuel delivery systems, evolution: (1) CARBURETOR (older, pre-1990s) — uses venturi effect (Bernoulli's principle) and mechanical metering; air drawn through narrowing passage creates low pressure, drawing up fuel from float bowl; mixed with air, drawn into intake; simple, no electronics needed, but imprecise control of fuel-air ratio across operating conditions; harder to meet emissions standards; affected by altitude, temperature; (2) FUEL INJECTION (modern, EFI/electronic fuel injection) — electronic control unit precisely meters fuel via INJECTORS (electrically-operated valves that spray fuel); much more accurate, adapts to conditions; required to meet emissions and fuel economy standards; subtypes: (a) THROTTLE BODY INJECTION (TBI) — one or two injectors at throttle body (early EFI); (b) MULTI-PORT INJECTION (MPI/MPFI) — one injector per cylinder, sprays into intake port near valve; (c) DIRECT INJECTION (DI/GDI) — sprays directly into cylinder at very high pressure; better atomization, more efficient, more power; common in modern engines; (d) PORT + DIRECT (some modern engines combine both). FUEL SYSTEM components: FUEL TANK; FUEL PUMP (electric, in tank usually); FUEL FILTER (removes contaminants); FUEL LINES; FUEL RAIL (manifold supplying injectors); INJECTORS; FUEL PRESSURE REGULATOR; RETURN LINE (sends excess fuel back to tank). Pressures: port injection 35-65 psi; direct injection 500-3000+ psi. ENGINE CONTROL UNIT (ECU/PCM/ECM) computes fuel needs based on: air flow (MAF or MAP sensor), oxygen sensor feedback (closed-loop control), engine speed, temperature, throttle position, accelerator, knock sensor, and many others. Stoichiometric ratio: 14.7:1 air:fuel by mass for gasoline = chemically optimal complete combustion; ECU varies this for starting (richer), warmup (richer), wide-open throttle (slightly rich for power), cruising (stoichiometric for efficiency and emissions). DIESEL fuel injection: very high pressure (15,000-30,000 psi modern common rail); diesel injected late in compression stroke; compression ignition (no spark plug). Carburetors still used in: lawn mowers, small engines, motorcycles (some), older cars. Diagnosing fuel system problems: weak fuel pump, clogged filter, bad injector, faulty sensor — affecting performance, economy, emissions, drivability.