TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
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ENGINE - CONTINUED
e.
EFI Operation. EFI operation consists of four stages: pre-injection, injection, end of injection, and fill. EFIs use
plunger and barrel to pump high-pressure fuel into combustion chamber. EFI components include solenoid, tappet,
plunger, barrel, and nozzle assembly made up of spring, nozzle check, and nozzle tip. Cartridge valve is made up
of solenoid, armature, poppet valve, and poppet spring.
Injector is mounted in an injector bore in cylinder head which has an integral fuel supply passage. Injector sleeve
separates injector from engine coolant in water jacket. Some engines use stainless steel sleeve which fits into
cylinder head with light press fit.
(1)
Pre-injection metering starts with plunger and tappet at top of fuel injection stroke. When plunger cavity is
full of fuel, poppet valve and nozzle check are both open. Fuel leaves plunger cavity when rocker arm
pushes down on tappet and plunger. Fuel flow blocked by closed nozzle check valve flows past open pop-
pet valve to fuel supply passage in cylinder head. If solenoid is energized, poppet valve remains open and
fuel from plunger cavity continues flowing into fuel supply passage.
(2)
To start injection, ECM sends current to solenoid on cartridge valve. Solenoid creates magnetic field
which attracts armature. When solenoid is energized, armature assembly lifts poppet valve so it contacts
poppet seat (closed position). Once poppet valve closes, fuel flow path leaving plunger cavity is blocked.
Plunger continues to push fuel from plunger cavity and fuel pressure increases. When fuel pressure reaches
approximately 5,000 psi (34,500 kPa), high-pressure fuel force overcomes spring force. This holds nozzle
check closed. Nozzle check moves off nozzle seat and fuel flows out of injector tip. This starts injection.
(3)
Injection is continuous while injector plunger moves in downward motion and energized solenoid holds
poppet valve closed. When injection pressure is no longer required, ECM stops current flow to solenoid.
When current flow to solenoid stops, fuel injector spring and fuel pressure opens poppet valve. High-pres-
sure fuel can now flow around open poppet valve and into fuel supply passage, resulting in rapid drop in
injection pressure. When injection pressure drops to approximately 3,500 psi (24,000 kPa), nozzle check
closes and injection stops.
(4)
When plunger reaches end of its stroke, fuel is no longer forced from plunger cavity. Plunger is pulled up
by tappet and tappet spring. Upward plunger movement causes plunger cavity pressure to drop below fuel
supply pressure. Fuel flows from fuel supply passage around open poppet and into plunger cavity as
plunger travels upward. When plunger reaches top of stroke, plunger cavity is full of fuel and fuel flow
into plunger cavity stops. This begins pre-injection.
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