DESCRIPTION AND OPERATION
Page 39
26
Figure 26 — Unit Injector — Injection and Pressure Drop Phases
Injection phase (C): The injection phase begins
when the fuel valve closes. The camshaft lobe
and rocker arm continue to press down on the
pump plunger and injection occurs as the path
through the fuel valve closes. The injection phase
continues as long as the fuel valve is closed.
Pressure drop phase (D): 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.
Unit injectors are categorized and coded with
regard to tolerances. Whenever a unit injector is
replaced, the replacement injector MUST be
programmed for the cylinder in which it is
installed. This is done by programming EECU
parameters using the VCADS PRO to set Injector
Trim parameters with the trim codes marked on
the injectors.
The dimension by which the injector nozzle
extends from the head is critical. This means that
machining the head in any way that changes this
nozzle extension is not permitted.
27
Figure 27 — Injector Coding
1. Pump Plunger
2. Fuel Gallery
3. Injector Nozzle
1. Serial No. 2. Unit Calibration No.
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