Chapters 43 and 44: Emission Control Systems, and Diagnosis and Repair

40% of a vehicle's emissions

Emissions from fuel evaporation and crankcase vapors

60% of a vehicle's emissions

Engine exhaust

Higher than normal NoX readings

Excessively high compression ratio, carbon deposits in the combustion chamber, low coolant, blocked cooling system, stuck thermostat or EGR system problems

Carbon Monoxide (CO)

Extremely toxic, colorless and odorless gas that is caused by rich air-fuel mixtures; Indicates incomplete burning of fuel or rich mixtures

Diverter valve

Keeps air from entering the system during deceleration to prevent backfire

Air check valve

Keeps exhaust gases from entering the air injection system

Rollover valve

Keeps liquid fuel from entering the vent line if the vehicle rolls over

Higher than normal HC's

Leaking injector, faulty pressure regulator or high fuel pressure; Blow-by, worn rings or blown head gasket; Bad PCV, catalytic converter or evaporative control system; Fouled spark plug, defective coil or open spark plug wire

Engine designs that can minimize emissions:

Lower compression ratios Small combustion chamber surface volume Reduced quench areas Decreased valve overlap Hardened valves and seats

Fuel tank pressure sensor

Monitors fuel tank pressure, it measures vapor pressure (DOES NOT measure fuel pressure)

Oxygen (O2)

Needed for the catalytic converter to burn HC and CO emissions, indicator of a vehicle's air-fuel mixture; High readings indicate a lean mixture

Ported vacuum

Not present at idle with the throttle plate closed

Purge valve

Operated electrically or by vacuum, it controls the flow of fuel vapors; generally allows flow when the engine is operating above idle and at operating temperature

Emission control systems

Positive crankcase ventilation (PCV) Evaporative emissions control (EVAP) Exhaust gas recirculation (EGR) Air injection/ Pulse air injection Catalytic converter Computer control

Evaporative emissions control system (EVAP)

Prevents evaporating fuel vapors from entering the atmosphere; Fuel vapors are stored in a charcoal canister until they can be burned in the engine

Non-vented fuel cap

Prevents fuel vapors from entering the atmosphere, the pressure and vacuum relief valve will vent if fuel tank pressure or vacuum levels get too high

CO readings

Related to the air-fuel ratio: A high CO reading would indicate an over-rich mixture A low CO reading would indicate a lean air-fuel mixture

PCV valve testing

Remove the valve from the grommet and shake it, the valve should rattle freely; Start the engine and plug the valve with your finger, you should feel vacuum

Particulates

Solid particles of carbon soot and fuel additives, a serious problem with diesel engines

Charcoal canister

Stores fuel vapors when the engine is not running

Hydrocarbons (HC's)

Unburned fuel and all other petroleum-based products, produced by incomplete combustion or fuel evaporation

Enhanced EVAP system

Uses athe control module, solenoids and a pressure sensor to monitor the condition of the fuel system

Positive crankcase ventilation (PCV)

Uses engine vacuum to draw blow-by gases from the crankcase into the intake manifold for burning; Reduces HC, CO, and particulates

Aspirator valve (reed valve, gulp valve)

Uses variations in exhaust back pressure to allow fresh air into the exhaust manifold

Smog

Visible cloud of airborne pollutants, formed when pollutants combine with oxygen and nitrogen in the presence of sunlight

Fuel tank air dome

A hump formed in the top of the fuel tank that allows for fuel expansion without spillage, it provides about 10% air space to allow for fuel heating and expansion

EGR

Allows burned exhaust gases to enter the intake manifold to reduce combustion chamber temperature and reduce NOx emissions

Carbon Dioxide (CO2)

Byproduct of normal combustion that occurs when one carbon atom combines with two oxygen atoms, readings should be high, 8-15%

Air pollution

Caused by an excess amount of harmful chemicals in the atmosphere, emission control systems are used on cars and trucks to reduce those harmful chemicals

PCV valve

Controls flow through the system, it is located in the valve cover, or intake manifold; Varies flow for idle, cruise, acceleration, wide open throttle, and engine-off conditions

Oxides of Nitrogen (NoX)

Directly related to engine combustion temperatures, above approximately 2500 ºF (1370 ºC), nitrogen and oxygen combine

Air injection system

Forces fresh air into the exhaust ports or catalytic converter to reduce HC's and CO's; causes exhaust gas to continue to burn in the exhaust manifold or catalytic converter

Pollutants produced by internal combustion engines:

Hydrocarbons (HC) Carbon monoxide (CO) Oxides of nitrogen (NOx) Particulates

Pulse air system

Instead of a pump, this system uses natural pressure pulses in the exhaust system to operate the aspirator valves