2.1.1 Fuel Injector
DETROIT DIESEL 53
upper helix advances the closing of the ports and the
beginning of injection.
General Instructions for Injector Care and Overhaul
The fuel injector is one of the most important and
precisely built parts of the engine. The injection of the
correct amount of fuel into the combustion chamber at
exactly the right time depends upon this unit. Because
the injector operates against high compression pressure
in the combustion chamber, efficient operation demands
that the injector assembly is maintained in first-class
condition at all times. Proper maintenance of the fuel
system and the use of the recommended type fuel filters
and clean water-free fuel are the keys to trouble-free
operation of the injectors.
Fig. 8. - Checking Rack and Plunger for Free
Due to the close tolerances of various injector parts.
Movement
extreme cleanliness and strict adherence to service
instructions is required.
injector in case the valve is accidentally held open by a
small particle of dirt. The injector plunger is then
Perform all injector repairs in a clean, well lighted room
returned to its original position by the injector follower
with a dust free atmosphere. An ideal injector room is
spring. Figure 3 shows the various phases of injector
slightly pressurized by means of an electric fan which
operation by the vertical travel of the injector plunger.
draws air into the room through a filter. This pressure
prevents particles of dirt and dust from entering the
On the return upward movement of the plunger, the high
room through the doors and windows. A suitable air
pressure cylinder within the bushing is again filled with
outlet will remove solvent fumes along
fuel oil through the ports. The constant circulation of
fresh cool fuel through the injector renews the fuel
supply in the chamber, helps cool the injector and also
effectively removes all traces of air which might
otherwise accumulate in the system and interfere with
accurate metering of the fuel.
The fuel injector outlet opening, through which the
excess fuel oil returns to the fuel return manifold and
then back to the fuel tank, is directly adjacent to the inlet
opening.
Changing the position of the helices, by rotating the
plunger, retards or advances the closing of the ports and
the beginning and ending of the injection period. At the
same time, it increases or decreases the amount of fuel
injected into the cylinder. Figure 2 shows the various
plunger positions from no-load to full-load. With the
control rack pulled out all the way (no injection), the
upper port is not closed by the helix until after the lower
port is uncovered. Consequently, with the rack in this
position, all of the fuel is forced back into the supply
chamber and no injection of fuel takes place. With the
Fig. 9. - Injector High Pressure Test
control rack pushed all the way in (full injection), the
upper port is closed shortly after the lower port has been
covered, thus producing a maximum effective stroke
and maximum injection. From this no injection position
to full injection position (full rack movement), the
contour
of
the
1972 General Motors Corp.
Page 4
