Emission Control System Testing, Service, and Repair

 Computer-controlled emission system service  Emission maintenance reminder  Inspecting emission control systems  Exhaust gas analyzer 16 Topics...  Catalytic converter service Oxy

Russell Krick

 Computer-controlled emission system

service

 Emission maintenance reminder

 Inspecting emission control systems

 Exhaust gas analyzer

(16 Topics)

 EGR system service

 Air injection system service

 Catalytic converter service

 Oxygen sensor service

 Emission control information sticker

 OBD II drive cycle

 Most emissions problems are caused

by a malfunction in a system unrelated

to the emission control system

 fuel system

 ignition system

 exhaust system

Scanning Emission

Systems

Scan Tool Readout

A DTC

B Description

C Possible causes

 The circuit turns on a dash light to

indicate the need for emission control system service

 After repairs, the light must be

turned off

 Refer to the service manual for

Inspecting Vacuum

Hoses

Four-Gas Analyzer

 Measures four gases:

 hydrocarbons (HC)

 carbon monoxide (CO)

 carbon dioxide (CO2)

 oxygen (O2)

Five-Gas Analyzer

 Measures five gases:

 hydrocarbons (HC)

 carbon monoxide (CO)

 carbon dioxide (CO2)

 oxygen (O2)

 oxides of nitrogen (NOx)

Five-Gas Analyzer

Using a Gas Analyzer

 Warm-up the analyzer

 about 10 minutes

 Zero and calibrate the analyzer

 zero the meter while sampling shop air or calibration gas

 Warm the vehicle to operating

temperature

 Insert a probe into the tail pipe through

Analyzer Test Procedures

 Two speed idle test

Using a Gas Analyzer

Exhaust Gas Analyzer

Readings

Carbon Monoxide

 CO

 Measured in percentage (%) by volume

 Indicates incomplete burning of fuel or

rich mixtures during combustion caused by insufficient air or excess fuel

 Normal readings are below 1.5%

Oxides of Nitrogen

 NOx

 Measured in parts per million (PPM) by

volume

 Formed when nitrogen and oxygen in

the cylinder combines

 Occurs when combustion chamber

temperatures are high

Carbon Dioxide

 CO2

 Measured in percentage (%) by volume

 Byproduct of normal combustion that

occurs when one carbon atom combines with two oxygen atoms

 Readings should be high, 8–15%

 O2

 Measured in percentage (%) by volume

 Typical readings should be 1–2% on a

fuel-injected engine

 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

 Exhaust gas readings are taken

 idle and a set rpm (e.g 2500 rpm)

 The vehicle may be checked for a

catalytic converter, fuel inlet restrictor, and other emission control systems

IM 240

 The vehicle is operated on a

dynamometer at speeds up to 55 mph (89 kmh) for 240 seconds while

exhaust gases are measured

 The evaporative emissions system may

be tested:

 purge test

 pressure test

Purge Test

 Measures the flow of fuel vapors into

the engine while performing the IM 240 test

 A flow meter is installed into the purge

line between the canister and the intake manifold

A computer compares the purge rate to

Pressure Test

 Checks the system for leaks into the

atmosphere

 Pressure test equipment is connected

to the evaporative emission system

 A computer meters low pressure

nitrogen into the system (0.5 psi,3.4 kPa)

 If the pressure drops too much, the

Refer to a vacuum hose

diagram

Vacuum

Solenoid

Service

Checking Solenoid

Valves

Checking Solenoid Valves

Use a multimeter

to check forvoltage tothe solenoid

Checking Solenoid

Valves

Checking Solenoid

Valves

 A faulty PCV system can increase

emissions, cause engine sludging, wear, and idle quality problems

 A leaking system can cause lean

mixture

 A plugged system can cause a rich

mixture

 Clean or replace the breather filter

 Check or replace the PCV valve

PCV 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

 The engine speed should drop 40–80

rpm on carbureted engines

PCV Testing

PCV Test / Gas

Analyzer

 Run the engine at idle; note the readings

 Pull the PCV valve out of the grommet;

note the readings

 Compare the readings

 If O2 and CO do not change, the PCV

system is plugged

 If O2 goes up more than 1% or CO goes

down more than 1%, the oil may be

 Symptoms:

 fuel odor

 fuel leakage

 fuel tank collapse

 excess pressure in fuel tank

Maintenance and

Repair

 Clean or replace the canister filter

when specified

 Inspect the fuel tank cap and pressure

test it for leakage

 Inspect all hoses for deterioration

 Replace with fuel-resistant hose

Canister Filter Replacement

Purge Valve Check

 If the flap remains in the cold air

position all the time, the engine may miss and hesitate

 If the flap stays in the hot air position,

the engine could perform poorly when

Maintenance and

Testing

 Visually inspect the following parts:

 hoses

 hot air tube

 exhaust manifold heat shroud

 sensor and vacuum motor operation

 Refer to a service manual

 Warm the engine to operating

temperature

 Quickly increase engine speed to

2500–3000 rpm

 The valve pintle should move

 With the engine idling, apply vacuum to

EGR Testing

EGR Testing

Testing (Electronic Type)

 A scan tool may allow you to observe

the valve status or drive the valve open manually

 An oscilloscope can be used to

observe the solenoid drive signal or feedback signal from a pintle position

Testing (Electronic Type)

Testing (Electronic Type)

Testing (Electronic Type)

 Replace the pump inlet filter if specified

 Adjust the belt tension

 Inspect the hoses and components

 Use an exhaust gas analyzer

 Run the engine and note the readings

 Disable the air injection system by

pinching or disconnecting the pump discharge hose

 O2 should drop 2–5%

 HC and CO should increase

Pump Output Check

The pump should produce

 Problems are caused by contamination,

overheating, and extended service

 A plugged converter can cause high

exhaust back pressure and loss of power

 Pellet-type converters may be drained

Plugged Catalytic

Converter

Backpressure Test

Gas Analyzer Test

 Run the engine and catalytic converter

to operating temperature, and note the readings

 If oxygen is 1–2% or more, and CO is

high (above 0.5 %), the converter is not oxidizing

Converter Replacement

 Sensors become coated or fouled with

exhaust byproducts

 Fuel economy and emissions may be

affected

 A “lazy” or “dead” O2 sensor will

change resistance or voltage slowly, or not at all, with changes in the exhaust gas oxygen level

 Connect a scan tool, check for

diagnostic trouble codes

 Observe the O2 sensor voltage in the

scan data

 A digital voltmeter may be used

 An oscilloscope may be used

Voltmeter Testing

Oscilloscope Testing

Oscilloscope Testing

Oscilloscope Testing

Dual Trace Scope

Emission

Systems

Wiring

O2 Sensor Replacement

 Disconnect the negative battery cable

 Unplug the sensor connector

 Spray the threads with penetrating oil

 Use a special sensor socket

 Inspect for contamination

O2 Sensor

O2 Sensor

 The emission control information

sticker contains important engine data

 evaporative emissions information

 schematics

 specifications

Vehicle Emission

Control Information

OBD II Drive Cycle

OBD II Drive Cycle

 The vehicle is driven on a road test or

dynamometer

 To begin, coolant has to be below a

specified temperature

 The vehicle is driven through various

conditions to allow computer to monitor all specified systems