electronic fuel injection. introduction strict emission standards require precise fuel delivery...
TRANSCRIPT
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.
Central Port Injection (CPI)
• Injector located in center of intake manifold
• 60 psi system• 6 or 8 poppet
valves attached to one TBI type injector
Poppet Nozzles
• Contains a check ball & extension spring
• Regulate the flow of fuel into cylinder
• Fuel flows when pressure exceeds 40 psi
• Ball reseats when pressure drops
Injector Testing
• Coil Test – Specific current supplied, measures voltage drop
• Injector Balance – Inj. Energized for a precise time frame, record fuel pressure drop
Injector Circuit Testing• Noid lights• Simple test light that plugs into injector
connector• Light flashes with each electrical pulse