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Figure 4-43.—Mechanical-timed injection. | Up
Construction Mechanic Basic Volume 01 - Construction methods and practices | Next
Timed Fuel Injection Systems - Continued |
A high-pressure electric pump draws fuel from
the fuel tank and delivers it to the metering unit. A
pressure relief valve is installed between the fuel pump
and the metering unit to regulate fuel line pressure by
bleeding off excess fuel back to the tank.
The metering unit is a pump that is driven by the
engine camshaft. It is always in the same rotational
relationship with the camshaft, so it can be timed to feed
the fuel to the injectors just at the right moment.
Each injector contains a spring-loaded valve that
is opened by fuel pressure, injecting fuel into the intake
at a point just before the intake valve.
The throttle valve regulates engine speed and
power output by regulating manifold vacuum, which, in
turn, regulates the amount of fuel supplied to the
injectors by the metering pump.
The more common type of timed fuel injection is
the electronic-timed fuel injection, also known as
electronic fuel injection (EFI) (fig. 4-44). Anelectronic
fuel injection system can be divided into four
subsystems:
1. Fuel delivery system
2. Air induction system
3. Sensor system
4. Computer control system
The fuel delivery system of an EFI system includes
an electric fuel pump, a fuel filter, a pressure regulator,
the injector valves, and the connecting lines and hoses.
Figure 4-44.—Electronic-timed injection.
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