Navistar International DT 466 Diagnostic/Troubleshooting Manual page 34

30
Fuel Injector Features
Two 48 volt 20 amp coils control a spool valve
that directs oil flow in and out of the injector. The
injector coils are turned on for approximately 800
µs (microseconds or millionths of a second). Each
injector has a single four pin connector that couples
to the valve cover gasket assembly.
Injector Coils and Spool Valve
An OPEN coil and a CLOSE coil on the injector move
the spool valve from side to side using magnetic force.
The spool has two positions:
• When the spool valve is open, oil flows into the
injector from the high-pressure oil rail.
• When the spool valve is closed oil exhausts from
the top of the fuel injector and drains back to the
crankcase.
Intensifier Piston and Plunger
When the spool valve is open, high-pressure oil
enters the injector pushing down the intensifier piston
and plunger. Since the intensifier piston is 7.1 times
greater in surface area than the plunger, the injection
pressure is also 7.1 times greater than ICP pressure
on the plunger.
Plunger and Barrel
Fuel pressure builds at the base of the plunger in
the barrel. When the intensifier piston pushes the
plunger down, the plunger increases fuel pressure in
the barrel 7.1 times greater than ICP. The plunger has
a diamond-like coating to resist scuffing.
Injector Needle
The injector needle opens inward, off its seat when
fuel pressure overcomes the Valve Opening Pressure
(VOP) of 28 mPa (4,075 psi). Fuel is atomized at high
pressure through the nozzle tip.
Fuel Injector Operation
The injection operation has three stages:
• Fill stage
• Main injection
• End of main injection
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
1 ENGINE SYSTEMS
Fill Stage
Figure 23 Fill stage
1.
2.
3.
4.
5.
During the fill stage both coils are de-energized and
the spool valve is closed. High-pressure oil from the
high-pressure oil rail is deadheaded at the spool valve.
Low-pressure fuel fills the four ports and enters
through the edge filter on its way to the chamber
EGES-270-1
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
CLOSE coil (off)
OPEN coil (off)
Needle (seated)
Disk check (seated)
Fuel inlet (4)