The THROTTLE BODY INJECTOR consists of
an electric solenoid coil, armature or plunger, ball or
needle valve and seat, and injector spring. Wires from
the computer connect to terminals on the injectors.
When the computer energizes the injectors, a magnetic
field is produced in the injector coil. The magnetic field
pulls the plunger and valve up to open the injector. Fuel
can then squirt through the injector nozzle and into the
The THROTTLE BODY PRESSURE REG-
ULATOR consists of a fuel valve, a diaphragm, and a
spring. When fuel pressure is low, the spring holds the
fuel valve closed, causing pressure to build as fuel flows
into the regulator from the fuel pump. When a preset
pressure is reached, pressure acts on the diaphragm.
The diaphragm compresses the spring and opens the
fuel valve. Fuel can then flow back to the fuel tank,
limiting the maximum fuel pressure at the injectors.
The THROTTLE POSITIONER is used on
throttle body assemblies to control engine idle speed.
The computer actuates the positioner to open or close
the throttle plates. In this way, the computer can
maintain a precise idle speed with changes in engine
temperature, load, and other conditions.
Although throttle body injection does not provide
the precise fuel distribution of the direct port injection,
it is much cheaper to produce and provide a much higher
degree of precision fuel metering than a carburetor.
What type of fuel injection system is the most
precise but is also the most complex?
Q10. In an electronic fuel injection system, what
sensor is used to detect engine speed?
On a throttle body injection system, what device
is used to control engine idle speed?
EXHAUST AND EMISSION CONTROL
components of the exhaust and emission
control systems. Describe the operation of the
exhaust and emission control systems.
Over the past several years, exhaust and emission
control has greatly increased because of stringent
antipollution laws and EPA guidelines. This has made
the exhaust and emission control systems of vehicles
invaluable and a vital part of todays vehicles.
The waste products of combustion are carried away
from the engine to the rear of the vehicle by the exhaust
system where they are expelled to the atmosphere. The
exhaust system also serves to dampen engine noise.
The parts of a typical exhaust system include the
following: exhaust manifold, header pipe, catalytic
converter, intermediate pipe, muffler, tailpipe, hangers,
heat shields, and muffler clamps.
The control of exhaust emissions is a difficult job.
The ideal situation would be to have the fuel combine
completely with the oxygen from the intake air. The
carbon would then combine with the oxygen to form
carbon dioxide (CO2); the hydrogen would combine to
form water (H2O); and the nitrogen present in the intake
would stand alone. The only other product present in
the exhaust would be oxygen from the intake air that
was not used in the burning of the fuel. In a real life
situation, however, this is not what happens. The fuel
never combines completely with the oxygen, and
undesirable exhaust emissions are created as a result.
The most dangerous of the emissions is CARBON
MONOXIDE (CO) which is a poisonous gas that is
colorless and odorless. CO is formed as a result of
insufficient oxygen in the combustion mixture and
combustion chamber temperatures that are too low.
Other exhaust emissions that are considered major
pollutants are as follows:
HYDROCARBONS (HC) are unburned fuel.
They are particulate (solid) in form, and, like carbon
monoxide, they are manufactured by insufficient
oxygen in the combustion mixture and combustion
chamber temperatures that are too low. Hydrocarbons
are harmful to all living things. In any urban area where
vehicular traffic is heavy, hydrocarbons in heavy
concentrations react with the sunlight to produce a
brown fog, known as photochemical smog.
OXIDES OF NITROGEN (NOX) are formed
when nitrogen and oxygen in the intake air combine
when subjected to high temperatures of combustion.
Oxides of nitrogen are harmful to all living things.
The temperatures of the combustion chamber
would have to be raised to a point that would melt
pistons and valves to eliminate carbon monoxide and
carbon dioxide emissions. This is compounded with the
fact that oxides of nitrogen emissions go up with any
increase in the combustion chamber temperature.
Knowing these facts, it can be seen that emission
control devices are necessary.