Count on us for fair, friendly service!
emission control systems and what they do
pollutants come from three sources: tailpipe, crankcase blowby vapors
and fuel vapors that evaporate from the fuel tank and carburetor.
blowby vapors are eliminated as a source of pollution by recirculating
the vapors into the engine for reburning through the Positive Crankcase
Ventilation (PCV) system.
PCV valve acts like a small calibrated vacuum leak, allowing manifold
vacuum to siphon air through the crankcase, taking with it moisture
and blowby gases that would otherwise pollute the atmosphere. As a side
benefit, it extends motor oil life.
emissions have been eliminated by sealing the fuel system and storing
vapors in a charcoal canister. When the engine starts, a purge valve
on the canister opens, allowing manifold vacuum to siphon vapors into
the intake manifold to be burned in the engine.
are 3 primary tail pipe pollutants:
monoxide (CO) is formed whenever there is not enough oxygen to completely
burn the fuel. The richer the mixture, the greater the quantity of CO
monoxide is the worst pollutant of the three because it is deadly. CO
emissions are reduced by keeping the air/fuel ratio lean, by preheating
incoming air and manifold to aid fuel vaporization, and by converting
the remaining CO into harmless carbon dioxide in the catalytic converter.
(HC) emissions are unburned gasoline. HC is not directly harmful, but
it contributes to smog formation. A fouled spark plug, a leaky exhaust
valve, or a fuel mixture so lean it won't ignite (lean misfire) can
all allow unburned fuel to enter the exhaust.
is reduced by maintaining a balanced air/fuel mixture, by making sure
compression and ignition are OK, and by reburning any HC remaining in
the catalytic converter.
of Nitrogen (NOX) are formed in the combustion chamber when temperatures
rise above 2,500>1|F and nitrogen begins to react with oxygen. Lean
air/fuel mixtures burn hotter and increase NOX.
not as poisonous as carbon monoxide, NOX irritates the eyes, nose and
lungs, and contributes to ozone depletion and acid rain formation.
is reduced by the Exhaust Gas Recirculation (EGR) system, and by three-way
EGR system allows a small amount of exhaust gas to be siphoned back
into the intake manifold to slightly dilute the incoming air/fuel mixture.
This lowers combustion temperatures to reduce NOX. It also helps prevent
catalytic converter contains a ceramic honeycomb or ceramic pellets
coated with a thin layer of platinum and palladium metal. In three-way
converters, a third catalyst (rhodium) is included to reduce NOX.
converter acts to reburn pollutants. To do so, it needs extra oxygen
received from an air pump or an aspirator valve.
show air flow through the system. Air travels from the air filter to
each cylinder where it mixes with hydrocarbons and carbon monoxide and
then escapes into the atmosphere through the exhaust system.
air pump is belt-driven and feeds air to the exhaust manifold through
a diverter valve and check valve. The diverter valve dumps excess air
back into the atmosphere when it's not needed (during deceleration,
some engines, a gulp valve is another part of the plumbing. The gulp
valve diverts air from the pump into the intake manifold. This momentarily
leans out the mixture during deceleration, preventing backfiring in
the exhaust from too much fuel.
some engines, an aspirator is used in place of an air pump. An aspirator
is a one-way valve that allows air to be siphoned into the exhaust system
between exhaust pulses.
computerized engine controls and three-way catalytic converters were
added, the air pump gained yet another control valve. When the engine
is cold, air is routed to the exhaust manifold to help reduce the initial
HC and CO emissions.
is not a problem when the engine is cold. As the engine warms up and
NOX starts to rise, the flow of air is diverted from the exhaust manifold
directly to the converter where it enters a chamber between the two