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
FIG 6-40 CLASS
LOW PRESSURE FUEL
INJECTOR
• 13-16 psi
operating
pressure
• Ball style
pintle
• Easily
replaceable
GM’s Crossfire Injection
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
Bosch & Delphi Multec
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.
Fuel Pressure Regulator
Fuel Pressure Regulator
Vacuum hose
connection
Fuel
return
Fuel 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
CMPI Connections
Electrical Connectors
Fuel Supply
Fuel Return
CMPI Up Close
Cylinder
Numbers
Fuel Pressure Regulator
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
Injector Cleaning
• Periodic cleaning
removes varnish &
other deposits
• Pressurized canister
dispenses cleaning
solution
• MUST disconnect
fuel pump!