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 engine.

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.

Q9. 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?

Q11. On a throttle body injection system, what device is used to control engine idle speed?

EXHAUST AND EMISSION CONTROL SYSTEMS

LEARNING OBJECTIVE: Identify 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 today's 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 (H₂ O); 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 (NO_X ) 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.