Volvo D16F Service Bulletin page 9

Volvo Trucks North America
Service Bulletin
Injector Operational Phases
Fill Phase
During the filling phase, the pump plunger is on its way
up, the camshaft lobe is passing its highest point and the
rocker arm is on its way toward the camshaft base circle.
The fuel valve is open, allowing fuel to flow into the unit
injector from the lower fuel gallery. Fuel flows into the
cylinder head and the unit injector pump cylinder. Filling
continues until the pump plunger reaches its upper
position.
Spill Phase
The spill phase begins when the camshaft turns to the
position at which the camshaft lobe forces the rocker arm
to push the pump plunger down.
The fuel can now flow through the fuel valve, through the
holes in the unit injector and out through the fuel gallery.
The spill phase continues as long as the fuel valve is
open.
Injection Phase
The injection phase begins when the fuel valve closes.
The camshaft lobe and rocker arm continue to press
down the pump plunger and injection occurs as the
route through the fuel valve closes. The injection phase
continues as long as the fuel valve is closed.
Pressure Drop Phase
The injection phase ends when the fuel valve opens
and pressure in the unit injector drops below the nozzle
opening pressure. The fuel flows through the open fuel
valve, through the unit injector holes and out through the
fuel gallery. Note that the fuel valve position (closed or
open) determines when the injection phase begins and
ends. The time during which the fuel valve is closed
determines the amount of fuel injected at each pump
stroke.
D
Date Group No.
230 247
11.2006
Page
9(11)