© 2012 Delmar, Cengage Learning

Emission Control System Service

Chapter 44

© 2012 Delmar, Cengage Learning

Objectives• Determine the causes of various emission

system problems• Perform service on the emission control system• Repair or replace defective emission control

parts• Diagnose emission problems using an exhaust

gas analyzer

© 2012 Delmar, Cengage Learning

Introduction• Environmental Protection Agency (EPA)

– Responsible for U.S. air quality regulation

– Emission control technicians must be licensed

• Focus of the chapter is to understand how to:– Service emission systems

– Diagnose problems

– Remove and replace components

– Diagnose emission problems

© 2012 Delmar, Cengage Learning

Inspecting Emission Control Systems

• Many states require periodic emission inspections– Visual inspection

• Look at hoses and wires• Check that all parts are in place• Run engine and listen for air leaks• Check condition and tension of the pump drive

belt• Inspect the air cleaner

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Computer-Controlled Emission Service

• New cars have sophisticated emission systems– Controlled by a computer, sensors, and

actuators

– May have emission maintenance reminder lights

– Many ways of testing devices and resetting the light

• Refer to emission control applications manual or manufacturer's service manual

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Crankcase Ventilation System Service

• Crankcase system must be air tight• Engine running and OCV valve installed

– Should be a vacuum at oil filter opening when

• Leak in the crankcase ventilation system – Not always readily apparent

© 2012 Delmar, Cengage Learning

© 2012 Delmar, Cengage Learning

Crankcase Ventilation System Service (cont’d.)

• Testing PCV valve– Pull PCV valve from its grommet

– With engine stopped, remove and shake valve

– With engine running, cover valve end

– Pull fresh air hose from air cleaner

• Check the breather hose to the air cleaner– Kinks

– Restriction

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Evaporative Control System Service

• Fuel evaporation– Major cause of air pollution

• Evaporative emission controls – Installed on gasoline filler nozzles

– Vehicles have their own on-board evaporative systems

– Often neglected until driveability problem occurs

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Evaporative System Maintenance

• Fresh air is drawn into the canister during purging– Some canisters have a replaceable filter

• Service interval is usually every two years– More often in dusty conditions

• Check condition of all system hoses– Use fuel hose or hose designed to be used with

fuel vapors

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Evaporative System Problem Diagnosis

• Considerations– Leaking evaporative systems allow gasoline

vapors to escape into the air

– Check liquid/vapor separator if there is liquid fuel in charcoal canister

– Loud rush of air entering the tank when cap is pulled indicates a venting problem

– EVAP systems on OBD II vehicles self-test for leaks

© 2012 Delmar, Cengage Learning

© 2012 Delmar, Cengage Learning

EGR System Service• Problems with the EGR system are common

– Poor EGR performance affects speed density fuel injection systems

• Testing of all types of valves requires:– Test valve operation

– Clear passageways

– Check sources of vacuum

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Air Injection System Service• Visual inspection

– Look for rusty check valves and air manifolds

– Check condition of hoses mounted near exhaust parts

– Inspect air pump drive belt

• Several problems in an air injection system– Exhaust noise under the hood

– Backfiring on deceleration

– Air pump noisy or frozen

– Emission test failure

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Catalytic Converter Service• Common failure of OBD II vehicles

– Overheating caused by a misfiring cylinder

• Plugged converter – Restricts engine exhaust flow

• Do not just replace the converter– Determine whether there is another problem

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Converter Testing• Cat must be heated: at least 600°F

– Converter light off: converter begins to oxidize

– Temperature is measured with a high-temperature pyrometer

– Best test for a converter: emission analyzer

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Catalytic Converter Replacement

• Replacement converter – Often bolted on with new gaskets

– Some require welding

– Use an EPA-approved equivalent replacement

– Installation of a used converter is illegal unless it has been tested and certified

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Analyzing Exhaust Emissions• Important points

– Air is mostly nitrogen and oxygen

– Burning of fuel is called oxidizing

– Compression must be enough to push molecules close together

– Raw fuel going out the tailpipe can be measured as HC

– If air-fuel mixture is too rich, there will not be enough O2

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Emission Analyzers• Measures content of gases in exhaust through a

probe installed in exhaust pipe of a running engine– Two-gas analyzer

• Older • Measures HC and CO

– Five-gas analyzer

• Measures HC, CO, CO2, O

2, and NO

x

• Exhaust gases – Measured in different ways

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Hydrocarbons• HCs are oxidized by the catalytic converter and

air injection system– One ppm means that out of every million parts of

an exhaust sample, one part is HC

• Most common cause of high HC: unburned fuel– Ignition problems

– Not enough air or too much air

– Incorrect air-fuel ratio

• A lean mixture can cause fluctuating HC readings, while CO remains mostly fixed

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Carbon Monoxide (CO)• CO should be CO

2

– Not enough CO2

• Rich air-fuel mixture causes incomplete combustion

• CO – Measured as a percentage of the total exhaust

• High readings can be caused by a rich mixture, retarded ignition timing, or a worn engine

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Carbon Dioxide• By-product of complete combustion

– Read as percent of total

– Reading will not be accurate if the air pump is running during a test

– Readings are taken after the catalytic converter

© 2012 Delmar, Cengage Learning

© 2012 Delmar, Cengage Learning

Oxygen (O2)• Air-fuel mixture is richer than stoichiometric

– Level of O2 will be lower

• Diagnosis with O2

– Nor formed during combustion

– Should be consumed during each combustion cycle

– Consumed by a catalytic converter

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Oxides of Nitrogen• Air is made up of 78% N and 21% O2

– Methods to achieve lower NOX production

• Reducing the compression ratio• Prevented from forming by EGR valve• Reduced after they are formed by the reduction

catalytic converter

• EGT problems – Biggest contributor to high NOX emissions

• Five-gas analyzer tips– Generic five-gas emissions specifications

© 2012 Delmar, Cengage Learning

Catalytic Converter Tests• Broken substrate

– Tap lightly with a rubber mallet to see if it rattles

• Cranking test for CO2

– Tells the condition of a catalytic converter• Catalytic converters on OBD II cars are tested

automatically

• During a converter test:– There should be no exhaust leaks

– Air injection is off and cat is hot

– Engine speed is 2,000 rpm

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Catalytic Converter Tests (cont’d.)

• Additional tests– Snap test

• Can be done only when there is fuel control

– Cat testing using CO2 conversion

• Used when results of an O2 storage test are marginal

– Intrusive testing• Hole is drilled in the exhaust before the cat and an

insert is installed to accept a positive probe attachment