18-02-2012, 04:12 PM
ELECTRONIC FUEL INJECTION
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
LOW PRESSURE FUEL INJECTOR
13-16 psi operating pressure
Ball style pintle
Easily replaceable
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
Central Multi-Port Injection (CMPI)
Similar to CPI
Individual injectors, with poppet valves
