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

Gasoline and Diesel Fuel Injection: Operation, Diagnosis, and Service 693
Figure 29–42 Schematic of a General Motors 2.8 litre gasoline fuel injection system with a mass airflow sensor.
Many European and Asian vehicles use a cold-start fuel injector (as does this vehicle); however, cold-start injectors
are not common in domestic vehicles, which typically use a major increase in injector pulse-width (“on” time) or a
primer pulse (extra injector pulse) for cold engine starting. (Courtesy General Motors)
this did not allow the precise control required to
meet new standards. Electronic systems were introduced
in the mid to late 1990s. We will start with
conventional fuel injection.
CONVENTIONAL
(MECHANICAL) FUEL INJECTION
Conventional fuel injection uses, for the most part, all
mechanical components.There is limited electrical use.
Other than glow-plug circuits, solenoids, block heaters,
and fuel heaters, fuel delivery is governed by a mechanical
injection pump. See Figure 29–44. Although
here are variations between makes and engine types,
the following is common with most systems.
■ Fuel tanks—Very similar to gasoline vehicles;
multiple tanks are often used for long distance
vehicles such as vans or pick-up trucks. The fuel
supply line in the tank usually contains a prefilter
to limit large contaminants from entering
the system.
■ Lift pump—Transfers fuel from the fuel tank,
through the fuel filter and on to the delivery
system. This may be an electric pump or a
mechanical pump driven by the engine.
■ Fuel filter—Very important with a diesel engine
as any small particles or abrasives that get past
the filter may cause damage to the injection
pump or injectors. See Figure 29–45. Hand
priming pumps are often found on the fuel filter;
they are used to remove trapped air from the fuel
system and to force fuel to the injection pump.
Many late-model systems remove air
automatically.
■ Water/fuel separators—Water in the fuel creates
a number of driveability problems as well as
system damage. Water is heavier than diesel fuel
and will accumulate at the bottom of the
separator, where it is drained as part of regular
maintenance. Some separators have a sensor
that illuminates a warning light on the
instrument panel when the water reaches a
given level. See Figure 29–46. Many late-model
systems incorporate the fuel filter, water
separator, and fuel heater in one unit.