Gasoline and Diesel Fuel Injection: Operation ... - Pearson Canada

Gasoline and Diesel Fuel Injection: Operation, Diagnosis, and Service 697
Figure 29–50 Diesel fuel leak testing. Use cardboard to test
for leaks, NEVER your hand! (Courtesy Ford Motor Co.)
Figure 29–49 Fuel passing through the delivery valve to
the injector. (Courtesy Ford Motor Co.)
Figure 29–51 Movement of the
control rack in an in-line injection
pump changes the fuel delivery
volume. (Courtesy Robert Bosch)
Fuel Control—In-line Injection
Pump
Remember that diesels do not use a throttle plate;
under most operating conditions the engine takes in
far more air than it requires. Power and speed are
controlled by the amount of fuel injected; more fuel
equals higher speed and greater power.
Note the control rack in Figure 29–51, which is
connected to the accelerator pedal. As the rack is
moved in or out, it rotates a gear and control sleeve,
which turns the plunger.
A tapered groove, called the helix, is machined
into the plunger. This increases or decreases the
amount of fuel as the plunger is rotated. The helix
controls fuel volume by opening or restricting a passage
to the spill port: a large opening means less fuel
is left in the barrel for injection, a restricted opening
leaves more fuel in the barrel and a greater volume
of fuel is injected. See Figure 29–52.
Governors
Governors are usually incorporated into the fuel injection
pump where engine speed is controlled by
limiting the amount of fuel supplied to the injectors.
The most common type of in-line pump governor
uses flyweights, which are held in by spring pressure.
See Figure 29–53. At higher RPM, centrifugal
force causes the flyweights to move outward against
the spring; this movement limits fuel-rack travel,
which in turn restricts fuel delivery and prevents engine
over-revving.