Emission control systems
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Emission Control Systems. Vehicle Pollution Sources. 3 areas of a vehicle that can pollute… tailpipe emissions fuel tank vapors (and carburetor vapors) crankcase blow-by gases. Major Engine Pollutants.

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Emission Control Systems

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Emission control systems

Emission Control Systems


Vehicle pollution sources

Vehicle Pollution Sources

  • 3 areas of a vehicle that can pollute…

    • tailpipe emissions

    • fuel tank vapors (and carburetor vapors)

    • crankcase blow-by gases


Major engine pollutants

Major Engine Pollutants

  • hydrocarbons: produced when some or all of the fuel does not get burned during combustion, or from raw gasoline vapors

    • tailpipe emission

    • fuel tank & carburetor emission

  • carbon monoxide: produced when there is insufficient oxygen to support combustion

    • tailpipe emission

  • oxides of nitrogen: produced when combustion temperatures exceed 1400°C / 2500°F

    • tailpipe emission


Blow by emission control

Blow-by Emission Control

  • crankcase ventilation system handles blow-by gases

    • hydrocarbon emissions

  • road-draft tube used until 1962


Blow by emission control1

Blow-by Emission Control

  • Positive Crankcase Ventilation system (PCV system) in use since 1963


Checking pcv system

Checking PCV System

  • replace the Positive Crankcase Ventilation valve and check its hose (inexpensive)…

  • Tech Tip:

  • pull the PCV valve out of the engine while it’s running

  • place your finger under the valve

  • you should feel and hear suction & the valve should click


Fixed orifice tube pcv systems

Fixed Orifice Tube PCV Systems

  • a precisely determined hole size acts as the valve

  • no need for a spring and valve assembly


Evaporative emission control system

Evaporative Emission Control System

  • prevents raw HC’s (from gasoline) from being vented into the atmosphere

    • (in use since 1971)

  • charcoal canister absorbs fuel vapors when the engine is off & sends them to the intake manifold so they can be burned when the engine is running


Evaporative emission control systems

Evaporative Emission Control Systems

  • on 1996 & newer vehicles, PCM…

    • purges canister vapors via a purge solenoid

    • monitors vapor flow

    • monitors the system for leaks

      • vehicle may use a separate pump to pressurize system to see if pressure can be maintained

      • if PCM detects a leak, check engine light will illuminate


Reducing nox tailpipe emissions

Reducing NOx Tailpipe Emissions

  • Exhaust Gas Recirculation valve (EGR) allows some exhaust gas back into the intake air stream

    • used on most engines since mid-1970’s but not all

  • EGR dilutes/displaces fresh, incoming AFM which drops combustion temperature = < NOx


Emission control systems

  • EGR typically operates under light throttle, cruising conditions on a warmed up engine

  • during warm up, WOT & at idle, it does not operate

EGR Valve

EGR Pipe


Egr valve styles

EGR Valve Styles

  • 1) mechanical EGR operated by engine vacuum

    • vacuum acts on a diaphragm to open the valve (fig. a)

    • some EGR valves use a computer controlled solenoid to modulate the vacuum signal to the diaphragm (fig. b)

    • others use an exhaust pressure sensor to help determine rate of exhaust gas flow (fig. c)

fig. c

fig. b

fig. a


Egr valve styles1

EGR Valve Styles

  • 2) digital or electronic EGR valve

    • PCM controls 1 or more solenoids to modulate EGR flow

    • no vacuum diaphragm is used

    • each solenoid has an integral pintle position sensor

      • this sensor “tells” the PCM the position of the pintle valve

    • the solenoids are pulsed on & off by the PCM many times/second when needed


Egr service

EGR Service

  • Inoperative EGR systems can lead to…

    • excessive NoX emissions (possible failure at AirCare)

    • detonation (knocking & pinging)

  • caused by…

    • defective diaphragm

    • weak vacuum signal

      • defective or incorrectly routed vacuum hoses

    • shorted or open solenoid

    • exhaust passage blocked with carbon


Egr service1

EGR Service

  • Excessive EGR operation can lead to…

    • rough idle

    • stalling

  • caused by…

    • improperly routed vacuum hoses

    • carbon on pintle valve seat

    • faulty EGR valve


Reducing tailpipe emissions

Reducing Tailpipe Emissions

  • catalytic converters reduce HC, CO & possibly NOx

    • used on all vehicles since mid-1970’s

  • HC & CO in the exhaust is oxidized by the catalyst which can contains platinum, palladium & rhodium

  • HC + O2 = CO2 & H20

  • CO + 02 = CO2

  • this is a two-way catalyst

  • needs ≈ 315°C / 600°F to operate


Three way catalysts

Three Way Catalysts

  • reduces HC, CO and NOx levels

  • NOx is converted to nitrogen & CO2

  • front ½ controls NOx & back ½ reduces HC & CO

    • contains cerium – has the ability to store oxygen

    • the oxygen is used to oxidize HC & CO

  • in use in Canada since 1988


Reducing tailpipe emissions1

Reducing Tailpipe Emissions

  • air injection systems

    • used on some engines, but not all

  • cold engine: air is injected into the exhaust manifold to oxidize HC & CO

  • warm engine: air is injected into the converter to oxidize HC & CO


Air injection systems

Air Injection Systems


Causes of excessive hydrocarbons

Causes of excessive hydrocarbons…


Causes of excessive carbon monoxide

Causes of Excessive Carbon Monoxide…

  • plugged air filter

  • high float level

  • choke not opening

  • faulty fuel injector

  • higher than normal fuel pressure

  • faulty EFI sensor


Causes of excessive nox

Causes of Excessive NOx…

  • carbon deposits

  • inoperative EGR valve

    • some valves are vacuum operated

    • others are electronically activated

  • higher than normal coolant temperatures


Pollution sources what controls them a recap

Pollution Sources & What Controls Them – a Recap…

  • 3 areas of a vehicle that can pollute…

    • tailpipe emissions

    • fuel tank vapors (and carburetor vapors)

    • crankcase blow-by gases


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