Introduction Strict emission standards require precise fuel delivery Computers used to calculate fuel needs EFI very precise, reliable & cost effective EFI provide correct A/F ratio for all loads, speeds, & temp ranges
The Fuel Injector Electromechanical device Controlled by PCM Engine rpm determines when injector opens How long it stays open determined by: –Engine temp –Engine load –Throttle pos. –O2 sensor voltage
Throttle Body Injection (TBI) First injection unit used Housing similar to Carb One or two injector One or two of these units mounted to intake manifold FIG 6-40 CLASS
Multi-Port Fuel Injection One injector per cylinder Mounts in intake manifold, sprays directly at intake valve Fired in groups or individually (SFI) Ram Tuning for denser air charge Lower A/F temps Leaner mixture during warm-up
Fuel Pressure Regulator Located at end of fuel rail Maintains constant pressure at injectors Internal chamber contains a diaphragm –Pressurized fuel on one side –Manifold vacuum & spring tension on other Manifold vacuum pulls up on diaphragm, metering fuel that is returned to tank Excess fuel pressure can overcome spring tension, allowing fuel to return to tank Increases in manifold pressure causes spring tension to push diaphragm down, blocking return line, increasing pressure in rail.