GMC 4000 Series Service Manual page 365

Sec. 6M
Page 354
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
V IE W A
INTAKE
H IG H PRESSURE (IN JE C T IO N ) FUEL
1 Spill Port
2 Metering Sleeve
3 Low Pressure Fuel Chamber
action is described in the following paragraphs:
NOTE: Key numbers in text refer to figure 3.
FUEL INTAKE (VIEW A, Fig. 3)
When plunger (9) is at the bottom of the stroke,
having been brought to that position by the plunger
return spring and tappet which is contacting the
base circle of the cam profile, the fuel flows from
the fuel chamber (3) through a ser ie s of inlet ducts
in the hydraulic head and fills that portion of the
plunger bore cavity above point "A" between the
top of the plunger and the bottom of the delivery
valve (5). The delivery valve (5) is closed due to
the tension of the delivery valve spring.
BEGINNING OF DELIVERY (VIEW B, Fig. 3)
As the rotating plunger (9) moves upward in
its stroke under cam action it closes the head
groove and inlet ports, thus trapping the admitted
fuel and building up pressure until the spring load­
ed delivery valve (5) is lifted and opened.
DELIVERY (VIEW C, Fig. 3)
As the plunger (9) continues its upward stroke
the fuel passes through the delivery valve bore and
is conveyed through the communicating ducts to the
annulus (8) in the plunger which connects to the
vertical distributing slot (7) on the plunger. This
vertical distributing slot registers, on successive
G M C S E R V I C E M A N U A L
V IE W B
TO NOZZLE
\
5 \
* ' ^ 9
BEGINNING
OF DELIVERY
4 Hydraulic Head Assembly
5 Fuel Delivery Valve
6 Fuel Passage in Plunger
Figure 3 — Fuel P um p in g Principle
pumping strokes, with each of the high pressure
outlets in the head so that this portion of the
plunger serves as a distributor as it is rotated
continually by its drive gear. The rotating and re­
ciprocating motions of plunger (9) are so phased
in relation to the outlet ducts that the vertical dis­
tributing slot (7) overlaps only one outlet duct dur­
ing each effective portion of each stroke.
END OF DELIVERY (VIEW D, Fig. 3)
er (9), the spill port (1) p asses upper edge (Point
"B") of the metering sleeve (2) and the fuel under
pressure escapes down the fuel passage (6) in the
center of the plunger, then into the chamber sur­
rounding the metering sleeve (2). The fuel p res­
sure then drops to equal the supply pressure. With
the drop in fuel pressure, the delivery valve (5)
closes during which action the piston portion of the
delivery valve (5) blocks the passage before the
valve reaches its seat and thus performs its func­
tion of reducing the residual pressure in the dis­
charge system . This is the end of the pumping
cycle.
4, except as otherwise indicated. Figure 4 shows
three positions of the fuel metering sleeve on the
injection pump plunger.
V IE W C
4
DELIVERY
OF DELIVERY
□ L O W PRESSURE (SUPPLY) FUEL
7 Distributing Slot in Plunger
8 Plunger Annulus
9 Plunger
After sufficient upward movement of the plung­
FUEL METERING PRINCIPLE
Key numbers in following text refer to figure
V IE W D
T
-4 5 17