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30

AIR POLLUTION ANDEMISSIONS CONTROL

Motor vehicles are major contributors to air pollu-tion, which causes a number of health-related andenvironmental concerns. High concentrations of con-taminants and smog were first noted in larger cities,usually in areas with limited air movement.

Automobile manufacturers, in cooperation withthe federal government, began researching thecauses and effects of vehicle emissions in the early1960s. They determined that there are three mainsources of automobile emissions:

■ Exhaust emissions - HC, CO and NOx■ Crankcase vapours - HC■ Fuel evaporation - HC

The factory installation of emission-control sys-tems first started with California vehicles in 1961;Canada and the remaining U.S. states joined in a fewyears later. Federal laws were enacted to ensure thatall automobiles, domestic and imported, must meetfederal control standards before being offered forsale in Canada and the U.S.

MAJOR POLLUTANTS

■ Hydrocarbons (HC). Gasoline is made ofhydrocarbons, which are consumed in the engineduring the combustion process. Any conditionthat causes a misfire (or poor combustion) willraise HC levels. Ignition problems, very leanmixtures, and vacuum leaks are major causes ofhigh HC. Fuel arrives at the engine as ahydrocarbon; if it leaves as unburned fuel, it’sstill a hydrocarbon.

■ Carbon monoxide (CO) is formed when thereis insufficient oxygen during combustion. CO isformed when one carbon atom from the fuelcombines with one oxygen atom from the air.High CO readings are usually the result of anoverly rich mixture.

CO is a poisonous gas that kills by replacingthe oxygen in red blood cells. Never run anengine inside without fitting adequate exhaustextraction hoses.

■ Oxides of nitrogen (NOx) are formed whennitrogen and oxygen from the air combine at

Emission Control DeviceOperation, Diagnosis,and Service

OBJECTIVES: After studying Chapter 30, you shouldbe able to:

1. Prepare for the interprovincial Red Seal certificationexamination in Appendix VIII (Engine Performance)on the topics covered in this chapter.

2. Describe how the PCV system operates and how todiagnose a fault with the system.

3. List two methods for diagnosing problems with theAIR system.

4. Describe how the evaporative emission controlsystem works and how to test for its properoperation.

5. Discuss the purpose and function of the EGR systemand how to diagnose EGR operational problems.

6. Explain how to test a catalytic converter forobstructions and operating efficiency.

7. Describe the operation of a hybrid vehicle.8. Explain the electrochemical reaction inside a fuel cell.

Emission Control Device Operation, Diagnosis, and Service 707

very high temperatures; major NOx formationbegins at temperatures above 1390°C (2500°F).Any condition that raises combustion chambertemperatures will increase NOx , e.g., lean air-fuel mixtures, over-advanced ignition timing, andmalfunctioning exhaust gas recirculation (EGR)systems.

■ Particulates, composed mainly of carbon, are amajor pollutant with diesel engines. The blacksmoke from a diesel under acceleration is usuallycaused by a rich air-fuel mixture or a restrictedair cleaner.

SMOG

The common term used to describe air pollution issmog, a word that combines the two words smoke andfog. See Figure 30–1. Smog is formed in the atmos-phere when sunlight combines with unburned fuel(hydrocarbon, or HC) and oxides of nitrogen (NOx) pro-duced during the combustion process. Smog is ground-level ozone (O3), a strong irritant to the lungs and eyes.

CONTROL OF EMISSIONS

■ HC (unburned hydrocarbons). Excessive HCemissions (unburned fuel) are controlled by theevaporative system (charcoal canister), thepositive crankcase ventilation (PCV) system, theair-pump system, and the catalytic converter.

NOTE: Although upper-atmospheric ozone is desir-able because it blocks out harmful ultraviolet rays fromthe sun, ground-level ozone is considered to be un-healthy smog.

Figure 30–2 Notice the reddish-brown haze that is oftenseen over major cities.

Figure 30–1 Smog is ground-level ozone that looks likeeither smoke or fog.

■ CO (carbon monoxide). Excessive COemissions are controlled by the PCV system,the air-pump system, and the catalyticconverter.

■ NOx (oxides of nitrogen). Excessive NOx

emissions are controlled by the exhaust gasrecirculation (EGR) system and the catalyticconverter. An oxide of nitrogen (NO) is acolourless, tasteless, and odourless gas when itleaves the engine, but as soon as it reaches theatmosphere and mixes with more oxygen,nitrogen oxides (NO2) are formed, which appearas reddish-brown. See Figure 30–2.

■ Particulates. Excessive particulate emissionsare controlled (on very recent diesels) withelectronic fuel injection and new catalyticconverters designed to eliminate particulatematter.

POSITIVE CRANKCASEVENTILATION (PCV) SYSTEM

Most engines remove blow-by gases from thecrankcase with a positive crankcase ventilation(PCV) system. This system pulls crankcase vapours

HINT: Exhaust emissions depend on the condition ofthe engine, ignition system, and fuel system as well asthe proper operation of exhaust emission-control de-vices. Proper vehicle maintenance, including regular oiland oil filter, air filter, and fuel filter changes and otherscheduled service, contributes to the ability of the en-gine to operate properly and produce the lowest possi-ble emissions.

into the intake manifold, where they are sent to thecylinders with the intake charge. The vapours arethen burned in the combustion chamber. Undersome operating conditions, the blow-by gases areforced back through the inlet filter. See Figure 30–3.

NOTE: A blocked or plugged PCV system is a majorcause of high oil consumption, and contributes to manyoil leaks. Before expensive engine repairs are attempted,check the condition of the PCV system. See Figure 30–4.

PCV System Performance Check

A properly operating positive crankcase ventilationsystem should be able to draw vapours from thecrankcase and into the intake manifold. If the pipes,hoses, and PCV valve itself are not restricted, vac-uum is applied to the crankcase. A slight vacuum iscreated in the crankcase (usually less than 25 mm[1 in.] Hg if measured at the dipstick) and is also ap-plied to other areas of the engine. Oil drainback

708 CHAPTER 30

Figure 30–3 A positive crankcase ventilation (PCV) system includes a hose from the air-cleaner assembly so that filtered air can be drawn into the crankcase. This filtered air is then drawn by engine vacuum through the PCV valve and into the intake manifold,where the crankcase fumes are burned in the cylinder. The PCV valve controls and limitsthis flow of air and fumes into the engine. The valve shuts in the event of a backfire to prevent flames from entering the crankcase area. (Courtesy of Chrysler Corporation)

Figure 30–4 A dirty PCV vent filter inside the air cleanerhousing. The air enters the crankcase through this filterand then is drawn into the engine through the PCV valve.

DIRTY PCVVENT FILTER

AIR CLEANER HOUSING

T E C H T I P

Check for Oil Leaks with the Engine Off

The owner of an older vehicle equipped with a V-6 enginecomplained to his technician that he smelled burning oil,but only after shutting off the engine. The technicianfound that the rocker cover gaskets were leaking. Butwhy did the owner only notice the smell of hot oil whenthe engine was shut off? Because of the positivecrankcase ventilation (PCV) system,engine vacuum tendsto draw oil away from gasket surfaces. But when the en-gine stops, engine vacuum disappears and the oil remain-ing in the upper regions of the engine will tend to flowdown and out through any opening. Therefore, a goodtechnician should check an engine for oil leaks not onlywith the engine running but also shortly after shut-down.

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Emission Control Device Operation, Diagnosis, and Service 709

holes provide a path for oil to drain back into the oilpan. These holes also allow crankcase vacuum to beapplied under the cam or rocker covers and in thevalley area of most V-type engines. There are severalmethods that can be used to test a PCV system.

The Rattle Test

The rattle test is performed by simply removing thePCV valve and shaking it in your hand.See Figure 30–5.

■ If the PCV valve does not rattle, it is definitelydefective and must be replaced.

■ If the PCV valve does rattle, it does notnecessarily mean that the PCV valve is good. AllPCV valves contain springs that can becomeweaker with age and heating and cooling cycles.Replace any PCV valve with the exactreplacement according to vehicle manufacturers’recommended intervals, usually every 3 years or60 000 km (36 000 miles).

The Card Test

Remove the oil-fill cap (usually in the valve cover)and start the engine. See Figure 30–6.

Hold a 75 � 125 mm (3 � 5 in.) card over theopening (any other piece of paper can be used for thistest).

■ If the PCV system, including the valve andhoses, is functioning correctly, the card should be

NOTE: Use care on some overhead camshaft engines.With the engine running, oil may be sprayed from theopen oil fill opening.

held down on the oil-fill opening by the slightvacuum inside the crankcase.

■ If the card will not stay, carefully inspect thePCV valve, hose(s), and manifold vacuum portfor carbon build-up (restriction). Clean or replaceas necessary.

The Snap-Back Test

The proper operation of the PCV valve can bechecked by placing a finger over the inlet hole in thevalve when the engine is running and removing thefinger rapidly. Repeat several times. The valveshould “snap back.” If the valve does not snap back,replace the valve.

AIR PUMP SYSTEM

An air pump provides the air necessary for the oxi-dizing process inside the catalytic converter. See Fig-ure 30–7.

On late model systems, a computer controls theairflow from the pump by switching on and off vari-ous solenoid valves. When the engine is cold, the airpump output is directed to the exhaust manifold to

NOTE: This system is commonly called AIR, meaningair injection reaction. Therefore, an AIR pump doespump air.

NOTE: On some 4-cylinder engines, the card may vi-brate on the oil fill opening when the engine is runningat idle speed. This is normal because of the longer timeintervals between intake strokes on a 4-cylinder engine.

Figure 30–6 A typical PCV valve installed in a rubbergrommet in the valve cover.

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Figure 30–5 A typical positive crankcase ventilation(PCV) valve. A defective or clogged PCV valve or hose cancause a rough idle or stalling problem. Because the airflowthrough the PCV valve accounts for about 20% of the airneeded by the engine at idle, use of the incorrect valve foran application could have a severe effect on idle quality.

help provide enough oxygen to convert HC (un-burned gasoline) and CO (carbon monoxide) to H2O(water) and CO2 (carbon dioxide). This also helps toheat the exhaust gas oxygen sensor.When the enginebecomes warm and the engine is operating in closedloop, the computer operates the air valves to directthe air pump output to the catalytic converter. Whenthe vacuum rapidly increases (above the normal idlelevel), as during rapid deceleration, the computer di-verts the air pump output to the air cleaner assem-bly to silence the air. Diverting the air to the aircleaner prevents exhaust backfire during decelera-tion. See Figure 30–8. Three basic types of air pumpare the belt-driven air pump, the pulse air-driven airpump, and the electric motor-driven air pump. Allair-pump systems use one-way check valves to allowair to flow into the exhaust manifold and to preventthe hot exhaust from flowing into the valves on theair pump itself.

NOTE: These check valves commonly fail, resulting inexcessive exhaust emissions (CO especially). When thecheck valve fails, hot exhaust can travel up to and de-stroy the switching valve(s) and air pump.

710 CHAPTER 30

Figure 30–7 A typical belt-driven air pump. Air entersthrough the revolving fins. These fins act as a moving airfilter because dirt is heavier than air and therefore the dirtin the air is deflected off the fins at the same time the air isdrawn into the pump.

Figure 30–8 (a) When theengine is cold and before theoxygen sensor is hot enough toreach closed loop, the airflow isdirected to the exhaustmanifold(s) through one-waycheck valve(s). These valveskeep exhaust gases fromentering the switching solenoids and the air pump. (b) When theengine achieves closed loop, theairflow from the pump isdirected to the check valve andcatalytic converter.

Emission Control Device Operation, Diagnosis, and Service 711

Belt-Driven Air Pumps

The belt-driven air pump uses a centrifugal filterjust behind the drive pulley. As the pump rotates,underhood air is drawn into the pump and slightlycompressed. See Figure 30–9. The air is then di-rected to

■ The exhaust manifold when the engine is cold tohelp oxidize CO and HC into carbon dioxide(CO2) and water vapour (H2O)

■ The catalytic converter on many models to helpprovide the extra oxygen needed for the efficientconversion of CO and HC into CO2 and H2O

■ The air cleaner during deceleration or wide-open throttle (WOT) engine operation (seeFigure 30–10)

Electric Motor-Driven Air Pumps

This style of pump is generally used only during coldengine operation.

Pulse Air Devices

The exhaust ports are normally under pressure fromthe burned exhaust leaving the cylinder. When theexhaust valve closes, the velocity of the escaping ex-haust creates a vacuum in the port. This vacuum isused to draw fresh air from the air cleaner into theexhaust port. A one-way check valve prevents ex-haust gases from reversing into the air cleaner whenthe exhaust valve opens and pressure returns. See

Normal Operation of a TypicalAir Injection Reaction

Engine Operation (AIR) Pump System

Cold engine Air is diverted to the exhaust (open-loop operation) manifold(s) or cylinder head

Warm engine Air is diverted to the catalytic (closed-loop operation) converter

Deceleration Air is diverted to the air cleanerassembly

Wide-open throttle Air is diverted to the air cleanerassembly

Figure 30–9 A typical belt-driven air pump.

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Figure 30–11. Pulse air systems cannot be used withoxygen sensors.

Air Pump System Diagnosis

The air pump system should be inspected if an ex-haust emissions test failure occurs. In some cases, theexhaust will enter the air cleaner assembly, resultingin a rough running engine because the extra exhaustdisplaces the oxygen needed for proper combustion.With the engine running, check for normal operation:

Visual Inspection

Carefully inspect all air injection reaction (AIR) sys-tem hoses and pipes. Any pipes that leak air or ex-haust require replacement. The check valve(s)should be checked when a pump has become inoper-ative. Exhaust gases could have leaked past thecheck valve and damaged the pump. Exhaust gas inthe air cleaner is usually an indication of a leakingcheck valve. Check the drive belt on an engine-driven pump for wear and proper tension.

Four-Gas Exhaust Analysis

An AIR system can be easily tested using an exhaustgas analyzer. Follow these steps:

1. Start the engine and allow it to run untilnormal operating temperature is achieved.

2. Connect the analyzer probe to the tail pipe andobserve the exhaust readings for hydrocarbons(HC) and carbon monoxide (CO).

3. Using the appropriate pinch-off pliers, shut offthe airflow from the AIR system. Observe theHC and CO readings. If the AIR system isworking correctly, the HC and CO shouldincrease when the AIR system is shut off.

4. Record the O2 reading with the AIR system stillinoperative. Unclamp the pliers and watch theO2 readings. If the system is functioningcorrectly, the O2 level should increase by 1 to 4%.

712 CHAPTER 30

Figure 30–10 The air pump supplies air to the exhaust port of each cylinder.Unburned hydrocarbons (HC) are oxidized into carbon dioxide (CO2) and water (H2O),and carbon monoxide (CO) is converted to carbon dioxide (CO2).

Figure 30–11 Cutaway of a pulse air-driven air device. Itis used on many older engines to deliver air to the exhaustport through the use of the exhaust pulses acting on aseries of one-way check valves. Air from the air cleanerassembly moves through the system and into the exhaustport, where the additional air helps reduce HC and COexhaust emissions.

Emission Control Device Operation, Diagnosis, and Service 713

EVAPORATIVE EMISSIONCONTROL SYSTEM

The purpose of the evaporative (EVAP) emissioncontrol system is to trap and hold gasoline vapours.The charcoal canister is part of an entire system ofhoses and valves called the evaporative control sys-tem. See Figure 30–12. Before the early 1970s, mostgasoline fumes were simply vented to the atmosphere.

Charcoal or carbon granules have a natural ten-dency to absorb gasoline fumes (vapours) becausecarbon attracts carbon. See Figure 30–13. After be-ing absorbed by the canister, the gasoline vapoursare drawn by the engine vacuum back into the in-take manifold to be burned (see Figures 30–14 and30–15). This process of drawing in vapours from thecharcoal canister is called purging. How muchshould be purged and when is controlled by a vac-uum valve or a computer-controlled solenoid.

Diagnosing the EVAP System

Before vehicle emissions testing began in manyparts of the country, little service work was done onthe evaporative emission system. Common engine-performance problems that can be caused by a faultin this system include:

■ Poor fuel economy. A leak in a vacuum-valvediaphragm can result in engine vacuum drawingin a constant flow of gasoline vapours from thefuel tank. This usually results in a drop in fueleconomy. Use a hand-operated vacuum pump tocheck that the vacuum diaphragm can holdvacuum.

■ Poor performance. A vacuum leak in themanifold or ported vacuum section of vacuumhose in the system can cause the engine to run

Figure 30–13 Some vehicles, especially trucks equippedwith a carburetor or TBI, use a charcoal (carbon) filterinside the regular air filter located in the air cleanerhousing. The purpose and function of this charcoal insert isto absorb evaporating fumes that occur when the engine isturned off. These fumes can come from the carburetor orintake manifold. When the engine is started, the normalairflow through the charcoal insert draws the gasolinefumes into the engine, where they are burned. Many fuelinjection systems (from 2004 on) use a hydrocarbonabsorber in the hose between the air cleaner and throttlebody. This hydrocarbon trap is a thin-wall honeycomb discthat holds HC until the engine starts.

CHARCOAL FILTER

Figure 30–12 The evaporativeemission control system includes allof the lines, hoses,and valves plus the charcoalcanister. (Courtesy of ChryslerCorporation)

714 CHAPTER 30

Figure 30–14 A typical evaporative emission control system. Note that when the computer turns on the canister purge solenoid valve, manifold vacuum draws any stored vapours from the canister into the engine. Manifold vacuum also is applied to the pressure control valve and when this valve opens, fumes from the fuel tank are drawn into the charcoal canister and eventually into the engine. When the solenoid valve is turned off (or the engine stops and there is no manifold vacuum), the pressure control valve is spring loaded shut to keep vapours inside the fuel tank from escaping to the atmosphere.

rough. Age, heat, and time all contribute to thedeterioration of rubber hoses.

Enhanced exhaust emissions (I/M 240) testingtests the evaporative emission system. A leak in the

system is tested by pressurizing the entire fuel sys-tem to 7 kPa (1 psi) with nitrogen, a nonflammablegas that makes up 78% of our atmosphere. The pres-sure in the system is then shut off and the pressuremonitored. If the pressure drops below a set stan-

Emission Control Device Operation, Diagnosis, and Service 715

Figure 30–15 This charcoal canister is mounted underthe hood. Not all charcoal canisters are this accessible; infact, most are hidden away under the hood or in otherlocations on the vehicle.

CHARCOAL CANISTER

dard, then the vehicle fails the test. This test deter-mines if there is a leak in the system.

To test for proper airflow in the EVAP system, aflow gauge is required as shown in Figure 30–16.Most vehicle emission test sites require at least 1 L of volume per purge during the 240 second (4minute) test. Many vehicles today are capable offlowing up to 10 L or more per minute.

HINT: To help diagnose leaks with the evaporativecontrol system, start with a fuel tank that is three-quarters full, or more. Minor leaks will show up fasterwhen the volume of air in the tank is small: The pres-sure drops more quickly.

Figure 30–16 A typical purge flow testerconnected in series between the intake manifold (or control solenoid) and the charcoalcanister. Most working systems should be capable of flowing at least one litre per minute.Some vehicles have to be driven for testing because some vehicle computers only purgeafter a certain road speed has been achieved.

716 CHAPTER 30

Frequently Asked Question

When Filling My Fuel Tank, Why Should IStop When the Pump Clicks Off?

Every fuel tank has an upper volume chamber that allowsfor expansion of the fuel when hot. The volume of thechamber is between 10 and 20% of the volume of thetank. For example, if a fuel tank had a capacity of 80 litres(20 gallons), the expansion chamber volume would befrom 8 to 16 litres (2 to 4 gallons). A hose is attached atthe top of the chamber and vented to the charcoal can-ister. If extra fuel is forced into this expansion volume,liquid gasoline can be drawn into the charcoal canister.This liquid fuel can saturate the canister and create anoverly rich air–fuel mixture when the canister purge valveis opened during normal vehicle operation. This extra-rich air–fuel mixture can cause the vehicle to fail an ex-haust emissions test, reduce fuel economy, and possiblydamage the catalytic converter. To avoid problems, simplyadd fuel to the next dime’s worth after the nozzle clicksoff. This will ensure that the tank is full, yet not overfilled.

???OBD II EVAPORATIVE

CONTROL SYSTEMS

Part of the on-board diagnostic second generation(OBD II) standards includes monitoring for a leak inthe evaporative control system (EVAP).

OBD II Evaporative Systems Monitor

The EVAP system monitor tests for purge volumeand leaks. Most applications purge the charcoal can-ister by venting the vapours into the intake manifoldduring cruise. To do this, the PCM typically opens asolenoid-operated purge valve installed in the purgeline leading to the intake manifold.

A typical EVAP monitor first closes off the sys-tem to atmospheric pressure and opens the purgevalve during cruise operation. See Figure 30–17. Afuel-tank pressure sensor then monitors the ratewith which vacuum increases in the system. Themonitor uses this information to determine the

Figure 30–17 A typical OBD II EVAP system,which uses fuel tank pressure and purge flowsensors to detect leaks and measure purge flow.

Emission Control Device Operation, Diagnosis, and Service 717

EXHAUST GASRECIRCULATION SYSTEM

To reduce the emission of oxides of nitrogen (NOx),engines have been equipped with exhaust gas re-circulation (EGR) valves. See Figure 30–20. From1973 until recently, EGR valves were used on almostall vehicles. Because of the efficiency of computer-controlled fuel injection, some newer engines do notrequire an EGR system to meet emissions stan-dards. Some engines use intake and exhaust valveoverlap as a means of trapping some exhaust in thecylinder.

The EGR valve opens at speeds above idle on awarm engine. (NOx emissions are not high on a coldengine). When open, the valve allows a small portionof the exhaust gas (up to about 7%) to enter the in-take manifold. Here, the exhaust gas mixes with andtakes the place of some intake charge. This leavesless room for the intake charge to enter the combus-tion chamber. The recirculated exhaust gas is inert(chemically inactive) and does not enter into thecombustion process. The result is a lower peak com-bustion temperature. As the combustion tempera-ture is lowered, the production of oxides of nitrogenis also reduced.

The EGR system has some means of intercon-necting the exhaust and intake manifolds. See Fig-ure 30–21. The interconnecting passage is con-trolled by the EGR valve. On V-type engines, theintake manifold crossover is used as a source of ex-haust gas for the EGR system. A cast passage con-nects the exhaust crossover to the EGR valve. Thegas is sent from the EGR valve to openings in themanifold. On inline-type engines, an external tubeis generally used to carry exhaust gas to the EGRvalve. This tube is often quite long so that the ex-haust gas is cooled before it enters the EGR valve.

purge volume flow rate. To test for leaks, the EVAPmonitor closes the purge valve, creating a completelyclosed system. The fuel tank pressure sensor thenmonitors the leak-down rate. If the rate exceedsPCM-stored values, a leak greater than or equal tothe OBD II standard of 1.0 mm (0.040 in.) exists. Af-ter two consecutive failed trips testing either purgevolume or the presence of a leak, the PCM lights theMIL and sets a DTC.

DaimlerChrysler vehicles use an electric pumpto pressurize the fuel system to check for leaks byhaving the PCM monitor the fuel-tank pressuresensor. See Figure 30–18. The fuel-tank pressuresensor is often the same part as the MAP sensorand instead of monitoring intake manifold ab-solute pressure, it is used to monitor fuel tankpressure.

Figure 30–18 A DaimlerChrysler electric EVAP pressurepump located at the rear of the vehicle is used topressurize the fuel tank and the PCM monitors for leaks.

GAS TANKEVAP PUMP

T E C H T I P

Always Tighten 3 Clicks

Many diagnostic trouble codes (DTCs) are set becausethe gas cap has not been properly installed. To be surethat a screw-type gas cap is properly sealed, tighten thecap until it clicks three times. The clicking is a ratchet de-vice and the clicking does not harm the cap. Therefore, ifa P0440 or similar DTC is set, check the cap. Test capscan also be used when diagnosing the system as shown inFigure 30–19.

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Figure 30–19 An assortment of gas caps used duringtesting of the EVAP system.

1. Vacuum must be applied to the EGR valveitself. This is usually ported vacuum on older,carburetor-equipped and some TBI fuel-injectedsystems. The vacuum source on later vehicles isoften manifold vacuum controlled by thecomputer through a solenoid valve.

2. Exhaust back pressure must be present to closean internal valve inside the EGR to allow thevacuum to move the diaphragm.

Electronic EGR

Many engines since the mid-1990s have usedcomputer-controlled solenoids or stepper motors(called linear EGR) to control the flow of exhaust intothe intake manifold. See Figure 30–22 for an exam-ple of an assembly that uses three solenoids on a V-6engine. The vehicle computer controls all three sole-noids and can turn one, two, or all three on as neces-sary to provide the exact amount of EGR needed.Some vehicles use a linear EGR that contains a step-per motor to precisely regulate exhaust gas flow anda feedback potentiometer that signals the computerthe actual position of the valve. See Figure 30–23.

Diagnosing a Defective EGR Valve or System

If the EGR valve is not opening or the flow of the ex-haust gas is restricted, then the following symptomsare likely:

■ Ping (spark knock or detonation) duringacceleration or during cruise (steady-speeddriving)

■ Excessive oxides of nitrogen (NOx) exhaustemissions

718 CHAPTER 30

Figure 30–20 Typical vacuum-operated EGR valve. Theoperation of the valve is controlled by the computer bypulsing the EGR control solenoid on and off.

EGR VALVE

EGR VALVECONTROLSELENOID

Positive and Negative BackPressure EGR Valves

Many EGR valves are designed with a small valveinside that bleeds off any applied vacuum and pre-vents the valve from opening. Some EGR valves re-quire a positive back pressure in the exhaust system.This is called a positive back pressure EGR valve.At low engine speeds and light engine loads, theEGR system is not needed, and the back pressure init is also low. Without sufficient back pressure, theEGR valve does not open even though vacuum maybe present at the EGR valve.

On each exhaust stroke, the engine emits anexhaust pulse. Each pulse represents a positivepressure. Behind each pulse is a small area of lowpressure. Some EGR valves react to this low pres-sure area by closing a small internal valve, whichallows the EGR valve to be opened by vacuum.This type of EGR valve is called a negative backpressure EGR valve. The following conditionsmust occur:

T E C H T I P

Watch Out for Carbon Balls!

Exhaust gas recirculation (EGR) valves can get stuck par-tially open by a chunk of carbon. The EGR valve or sole-noid will test as defective. When the valve (or solenoid)is removed, small chunks or balls of carbon often fall intothe exhaust manifold passage. When the replacementvalve is installed, the carbon balls can be drawn into thenew valve again, causing the engine to idle roughly or stall.

To help prevent this problem, start the engine withthe EGR valve or solenoid removed. Any balls or chunksof carbon will be blown out of the passage by the exhaust.Stop the engine and install the replacement EGR valve orsolenoid. Wear safety glasses or stay in the vehicle dur-ing this operation.

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Emission Control Device Operation, Diagnosis, and Service 719

Figure 30–22 This V-6 uses three solenoids for EGR. Ascan tool can be used to turn on each solenoid. This willcheck whether the valve is working and if the exhaustpassages are capable of flowing enough exhaust to theintake manifold to affect engine operation when cycled.

DIGITALEXHAUSTGASRECIRCULATIONASSEMBLY

Figure 30–21 When the EGRvalve opens, exhaust flowsthrough the valve and into passages in the intake manifold.

If the EGR valve is stuck open or partially open, thenthe following symptoms are likely:

■ Rough idle or frequent stalling■ Poor performance/low power

The first step in almost any diagnosis is to per-form a thorough visual inspection. To check forproper operation of a vacuum-operated EGR valve,follow these steps:

1. Check the vacuum diaphragm to see if it canhold vacuum.

2. Apply vacuum from a hand-operated vacuumpump and check for proper operation. The valveitself should move when vacuum is applied, andthe engine operation should be affected. TheEGR valve should be able to hold the vacuumthat was applied. If the vacuum drops off, thenthe valve is likely to be defective.

NOTE: Positive back-pressure EGR valves requirethat a certain amount of exhaust restriction be presentto allow the valve to operate correctly. If low-restrictionaftermarket or custom exhaust systems have been in-stalled, the EGR valve may not function correctly. If thevalve does not open or does not open enough, the enginewill likely ping or spark knock during acceleration. Ex-haust NOx exhaust emissions are also likely to occur.

NOTE: Because many EGR valves require exhaustback pressure to function correctly, the engine shouldbe running at the specified RPM.

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Figure 30–23 A linear EGR valve.

DIAGNOSTIC STORY

The Blazer Story

The owner of a Chevrolet Blazer equipped with a 4.3 L,V-6 engine complained that the engine would stumble andhesitate at times. Everything seemed to be functioningcorrectly, except that the service technician discovered aweak vacuum going to the EGR valve at idle. This vehiclewas equipped with an EGR valve-control solenoid, calledan electronic vacuum regulator valve or EVRV byGeneral Motors Corporation. The computer pulses thesolenoid to control the vacuum that regulates the oper-ation of the EGR valve. The technician checked the serv-ice manual for details on how the system worked. Thetechnician discovered that vacuum should be present atthe EGR valve only when the gear selector indicates adrive gear (drive, low, reverse). Because the techniciandiscovered the vacuum at the solenoid to be leaking, thesolenoid was obviously defective and required replace-ment. After replacement of the solenoid (EVRV), the hes-itation problem was solved.

NOTE: The technician also discovered in the servicemanual that blower-type exhaust hoses should not be con-nected to the tail pipe on any vehicle while performing aninspection of the EGR system. The vacuum created by thesystem could cause false EGR valve operation to occur.

DIAGNOSTIC STORY

“I Was Only Trying to Help!”

On a Friday, an experienced service technician found thatthe driveability performance problem was a worn EGRvalve. When vacuum was applied to the valve, the valvedid not move at all. Additional vacuum from the hand-operated vacuum pump resulted in the valve popping allthe way open. A new valve of the correct part numberwas not available until Monday, yet the customer wantedthe vehicle back for a trip during the weekend.

To achieve acceptable driveability, the technicianused a small hammer and deformed the top of the valveto limit the travel of the EGR valve stem. The technicianinstructed the customer to return on Monday for theproper replacement valve.

The customer did return on Monday, but now ac-companied by his lawyer. The engine had developed ahole in one of the pistons. The lawyer reminded the tech-nician and the manager that an exhaust emission controlhad been modified. The result was the repair shop paidfor a new engine and the technician learned always to re-pair the vehicle correctly or not at all.

Emission Control Device Operation, Diagnosis, and Service 721

If the EGR valve is able to hold vacuum, butthe engine is not affected when the valve isopened, then the exhaust passage(s) must bechecked for restriction. See the Tech Tip “TheSnake Trick.” If the EGR valve will not hold vac-uum, the valve itself is likely to be defective andrequire replacement.

OBD II EGR SYSTEM MONITOR

The OBD II EGR emission monitor uses a varietyof methods to test EGR flow, depending on themanufacturer and the application. Most vehiclesuse the MAP sensor to test the EGR. During decel-eration, the computer commands the EGR on andwatches the MAP sensor response. The engine vac-uum should decrease if the EGR flow is sufficient,and the MAP sensor should detect this drop in vac-uum. If not enough change is noted, the test fails.The O2S sensor is also used by some systems tocheck the EGR. If the EGR efficiency level does notmeet a predetermined standard after two consecu-tive trips, the computer lights the MIL and sets oneor more DTCs.

CATALYTIC CONVERTERS

An exhaust pipe connected to the manifold or headercarries gases through a catalytic converter to the muf-fler and resonator (if used). In single exhaust systemsused on V-type engines, the exhaust pipe is designed tocollect the exhaust gases from both manifolds using aY-shaped design. Vehicles with dual exhaust systems

have a complete exhaust system coming from each ofthe manifolds. In most cases, the exhaust pipe must bemade up in several sections so that it can be assembledin the space available under the vehicle.

The catalytic converter is installed betweenthe manifold and the muffler to help reduce exhaustemissions. The converter has a heat-resistant metalhousing. See Figure 30–24. A bed of catalyst-coatedpellets or a catalyst-coated honeycomb grid is insidethe housing.

Catalytic Converter Operation

The converter contains small amounts of rhodium,palladium, and platinum. These elements act ascatalysts (entities that start a chemical reactionwithout becoming a part of the chemical reaction).See Figure 30–25. As the exhaust gas passesthrough the catalyst, oxides of nitrogen (NOx) arechemically reduced (that is, nitrogen and oxygenare separated) in the first section of the catalyticconverter. This is called the reduction section. Inthe second section of the catalytic converter, mostof the hydrocarbons and carbon monoxide remain-ing in the exhaust gas are oxidized to form harm-less carbon dioxide (CO2) and water vapour (H2O).This is called the oxidizing section. An air-injectionsystem or pulse air system is used on some enginesto supply additional air that may be needed in theoxidation process. See Figure 30–26. Since theearly 1990s, many converters also contain cerium,an element that can store oxygen. The purpose ofthe cerium is to provide oxygen to the oxidationbed of the converter when the exhaust is rich andlacks enough oxygen for proper oxidation. When

T E C H T I P

The Snake Trick

The EGR passages on many intake manifolds becomeclogged with carbon, which reduces the flow of exhaustand the amount of exhaust gases in the cylinders. Thisreduction can cause spark knock (detonation) and in-creased emissions of oxides of nitrogen (NOx).

To quickly and easily remove carbon from exhaustpassages, cut an approximately 300 mm (1 ft) lengthfrom stranded wire, such as garage door guide wire oran old speedometer cable. Flare the end and place theend of the wire into the passage. Set your drill on re-verse, turn it on, and the wire will pull its way throughthe passage, cleaning the carbon as it goes, just like aplumber’s snake in a drain pipe.

✔

Figure 30–24 Typical catalytic converter. The small tubein the side of the converter comes from the air pump. Theadditional air from the air pump helps oxidize the exhaustinto harmless H2O (water) and CO2 (carbon dioxide).

CATALYTIC CONVERTER

AIR TUBE

the exhaust is lean, the cerium absorbs the extraoxygen. The converter must have a varying rich-to-lean exhaust for proper operation:

■ A rich exhaust is required for reduction—strippingthe oxygen (O2) from the nitrogen in NOx

■ A lean exhaust is required to provide the oxygennecessary to oxidize HC and CO (combiningoxygen with HC and CO to form H2O and CO2)

Early catalytic converters are oxidizing only:helping to control HC and CO. They are know as two-way converters. Later converters added a reductionsection that helps to control NOx. These are known asthree-way converters.

If the catalytic converter is not functioning cor-rectly, check to see that the air-fuel mixture beingsupplied to the engine is correct and that the ignitionsystem is free of defects.

Nitrogen-Oxide-AdsorptiveCatalytic Converters

Conventional three-way converters are not effec-tive in converting NOx into nitrogen when exces-

sive oxygen from lean mixtures is present. NOAconverters attract NOx molecules during lean oper-ating conditions and release them when the mix-ture richens.

Four-Way Converters

Late in 2004, California became the first state to ap-prove a regulation reducing carbon dioxide (CO2)emissions from vehicle exhaust. Canada and theother states are expected to follow. The new regula-tion becomes effective with 2009 vehicles.

The Tap Test

This simple test involves tapping (not pounding)on the catalytic converter using a rubber mallet. Ifthe substrate inside the converter is broken, theconverter will rattle when hit. If the converter rat-tles, a replacement converter is required. See Fig-ure 30–27.

722 CHAPTER 30

Figure 30–25 A cutaway of a monolith substrate converter.

Figure 30–26 A cutaway of a three-way catalyticconverter showing the air tube in the centre of thereducing and oxidizing section of the converter. Note thesmall holes in the tube to distribute air from the AIR pumpto the oxidizing rear section of the converter.

Frequently Asked Question

Can a Catalytic Converter Be DefectiveWithout Being Clogged?

Yes. Catalytic converters can fail by being chemicallydamaged or poisoned without being mechanicallyclogged. Therefore, the catalytic converter should notonly be tested for physical damage (clogging) by per-forming a back-pressure or vacuum test and a rattletest but also for temperature rise, usually with a py-rometer or propane test, to check the efficiency of theconverter.

???

Figure 30–27 This catalytic converter blew up whengasoline from the excessively rich running engine ignited.Obviously, raw gasoline was trapped inside and all itneeded was a spark. No further diagnosis of this converteris necessary.

Emission Control Device Operation, Diagnosis, and Service 723

Testing Back Pressure with a Vacuum Gauge

A vacuum gauge can be used to measure manifold vac-uum at a high idle (2000 to 2500 rpm). If the exhaustsystem is restricted, pressure increases in the exhaustsystem. This pressure is called back pressure. Man-ifold vacuum will drop gradually if the engine is keptat a constant speed and the exhaust is restricted.

The reason the vacuum will drop is that all theexhaust leaving the engine at the higher enginespeed cannot get through the restriction. After ashort time (within 1 minute), the exhaust tends topile up above the restriction and eventually remainsin the cylinder of the engine at the end of the exhauststroke. Therefore, at the beginning of the intakestroke, when the piston traveling downward shouldbe lowering the pressure (raising the vacuum) in theintake manifold, the extra exhaust in the cylinderlowers the normal vacuum. If the exhaust restrictionis severe enough, the vehicle can become undriveablebecause cylinder filling cannot occur except at idle.

Testing Back Pressure with a Pressure Gauge

Exhaust system back pressure can be measured di-rectly by installing a pressure gauge in an exhaustopening. This can be accomplished in one of the fol-lowing ways:

1. To test at an oxygen sensor opening, remove theinside of an old, discarded oxygen sensor andthread in an adapter to connect it to a vacuumor pressure gauge.

2. To test at an exhaust gas recirculation (EGR)valve, remove the EGR valve and fabricate aplate.

3. To test at an air injection reaction (AIR) checkvalve, remove the check valve from the exhausttubes leading to the exhaust manifold. Use arubber cone with a tube inside to seal againstthe exhaust tube. Connect the tube to apressure gauge.

At idle the maximum back pressure should beless than 10 kPa (1.5 psi), and it should be less than15 kPa (2.5 psi) at 2500 rpm.

NOTE: An adapter can be easily made by inserting ametal tube or pipe. A short section of brake line worksgreat. The pipe can be brazed to the oxygen sensorhousing or it can be glued with epoxy. An 18 mm com-pression gauge adapter can also be adapted to fit intothe oxygen sensor opening. See Figure 30–28.

Testing a Catalytic Converter for Temperature Rise

A properly working catalytic converter should beable to reduce NOx exhaust emissions into nitrogen(N) and oxygen (O2) and oxidize unburned hydro-carbon (HC) and carbon monoxide (CO) into carbondioxide (CO2) and water vapour (H2O). During thesechemical processes, the catalytic converter shouldincrease in temperature at least 10% if the con-verter is working properly. To test, operate the en-gine at 2500 rpm for at least 2 minutes to fully warmup the converter. Measure the inlet and the outlettemperatures as shown in Figure 30–29.

OBD II Catalytic Converter Monitor

The catalytic converter monitor of OBD II uses anupstream and downstream heated oxygen sensor(HO2S) to test catalytic efficiency. See Figure30–30. When the engine combusts a lean air–fuelmixture, higher amounts of oxygen flow through theexhaust into the converter. The catalyst materialsabsorb this oxygen for the oxidation process,thereby removing it from the exhaust stream. If aconverter cannot absorb enough oxygen, oxidationdoes not occur. Engineers established a correlation

NOTE: If the engine is extremely efficient, the con-verter may not have any excessive unburned hydro-carbons or carbon monoxide to convert! In this case, aspark plug wire could be grounded out using a vac-uum hose and a test light (see Chapter 21) to createsome unburned hydrocarbon in the exhaust. This willheat the converter. Do not ground out a cylinder forlonger than 10 seconds or the excessive amount of un-burned hydrocarbon could overheat and damage theconverter.

Figure 30–28 A back pressure tool can be easily made byattaching a short section of brake line to the shell of an oldoxygen sensor. Braze or epoxy the tube to the shell.

724 CHAPTER 30

Figure 30–29 The temperature of the outlet should be at least 10% hotter than the temperature of the inlet. This converter is very efficient. The inlet temperature is 230°C (450°F).Ten percent of 230°C is 23°C (450°F, 45°F). In other words, the outlet temperature should be at least 253°C (495°F) for the converter to be considered okay. In this case, the outlet temperature of 274°C (525°F) is more than the minimum 10% increase in temperature. If the converter is not working at all, the inlet temperature will be hotter than the outlet temperature.

between the amount of oxygen absorbed and con-verter efficiency.

The OBD II system monitors how much oxygenthe catalyst retains. A voltage waveform from thedownstream HO2S of a good catalyst should havelittle or no activity. See Figure 30–31. A voltagewaveform from the downstream HO2S of a degradedcatalyst shows a lot of activity. In other words, thecloser the activity of the downstream HO2S matchesthat of the upstream HO2S, the greater the degree ofconverter degradation. In operation, the OBD II

monitor compares activity between the two exhaustoxygen sensors.

Diesel Particulate CatalyticConverters

Diesel exhaust contains some HC and NOx, but ex-cess particulates are the main emissions. There area number of diesel converters that use high internaltemperatures to incinerate the particulates and turnthem into ash.

Emission Control Device Operation, Diagnosis, and Service 725

DIESEL EMISSION CONTROLS

Diesel engines have no throttle plate; they take in farmore air than is needed, except during the maximumpower demands. Because of this, combustion is verycomplete compared to a gasoline engine, and emis-sions differ. See Figure 30–32.

Hydrocarbons (HC) and carbon monoxide (CO)emissions are generally low. Oxides of nitrogen (NOx)may be present because of the high temperaturesand pressures during combustion; however, theworst emission is particulate matter. Particulates,composed primarily of carbon, are visible (black

Figure 30–30 The OBD II catalytic converter monitorcompares the signals of the upstream and downstreamoxygen sensors to determine converter efficiency.

Figure 30–31 The waveform of an O2S downstreamfrom a properly functioning converter shows little, if any,activity.

T E C H T I P

Catalytic Converters Are Murdered

Catalytic converters start a chemical reaction but do notenter into the chemical reaction. Therefore, catalyticconverters do not wear out and they do not die of oldage. If a catalytic converter is found to be defective (non-functioning or clogged), look for the root cause. Remem-ber this:

“Catalytic converters do not commit suicide—they’re murdered.”

Items that should be checked when a defective cat-alytic converter is discovered include all components ofthe ignition and fuel systems. Excessive unburned fuel cancause the catalytic converter to overheat and fail. Theoxygen sensor must be working and fluctuating from 0.5to 5 Hz to provide the necessary air–fuel mixture varia-tions for maximum catalytic converter efficiency.

✔

Figure 30–32 Excess air in adiesel engine contributes to amore complete combustion.(Courtesy Ford Motor Co.)

smoke) and are created by incomplete combustion.Rich fuel mixtures or an air intake restriction arecommon causes of increased particulate formation.

Federal emission standards for diesel engines be-gan in 1988 and have become more stringent sincethat time. As an example, particulate emission limitswere lowered from 60 grams per brake horsepower-hour in 1988 to 10 grams per horsepower-hour in1994. This required the need for catalytic converterson some exhaust systems.

In 1997, OBD II standards for diesel engineswere introduced; EGR systems were now monitoredand in 1998, engine misfire and glow plug malfunc-tions were added. A malfunction indicator lamp(MIL) on the instrument panel turns on to indicate asystem deterioration or failure.

Diesel engines are analyzed with an opacity me-ter (clamped to the exhaust pipe), which uses a lightbeam to measure exhaust density under different op-erating modes. Common emission controls includecatalytic converters for particulates, EGR valves forNOx, and crankcase depression regulator valves, aform of PCV valve used to control crankcase hydro-carbon emissions.

Diesel palladium-oxidation particulate-reductionconverters require low-sulphur diesel fuel, whichwas mandated in Canada beginning in 1995. High-sulphur fuels will render the converter inactive.Bosch and a number of European manufacturershave developed a new sintered metal (vs. traditionalceramic) particulate-filter converter that is expectedto last for the life of the vehicle. Production is ex-pected to begin in 2005–2006.

The introduction of electronically controlled fuelinjection assures a more precise fuel delivery thatbrings emissions to an even lower level.

EMISSIONS TESTING CENTRES

The British Columbia AirCare and the Ontario DriveClean programs are designed to identify vehicleswith high emissions, and to improve air quality byreducing harmful pollutants. Drive Clean inspectsvehicles in southern and eastern Ontario, while Air-Care covers the Greater Vancouver and Fraser Val-ley regions, areas in both provinces experiencing airpollution problems. Although there are differencesbetween the two programs, they are similar. The fol-lowing is typical.

■ Older vehicles, prior to 1991 must be checkedevery year during a steady state 40 km/h (25 mph)tailpipe test.

■ Newer vehicles, from 1992 to date, are inspectedevery two years. They go through a morecomprehensive test. See Figure 30–33.

■ Maximum allowable emissions, listed as partsper million (ppm), percent (%) or grams perkilometre (g/km), vary with the year and modelof the vehicle. See Figure 30–34.

■ New vehicles are exempt for the first year (orfirst two years).

■ The vehicle must either pass the test or have aconditional pass before licence plates will beissued.

Vehicles brought to the test centre are checkedvisually for a catalytic converter, the gas cap is re-moved for pressure testing and the vehicle exhaustis measured for hydrocarbons (HC), carbon mo-noxide (CO) and oxides of nitrogen (NOx) whilerunning at speed on a dynamometer. Special dy-namometers are often used for all-wheel drives.See Figure 30–35.

Owners of vehicles that fail the test will receivea conditional pass if they have the vehicle diagnosedand repaired by an AirCare Certified technician atan AirCare certified repair centre. There is a repaircost limit designed to ensure emissions are reducedwhile limiting the financial burden for the owner.Ontario has a fixed limit; British Columbia’s limit istied to the model year.

Vehicles repaired by a non-certified shop will notqualify for a conditional pass; the vehicle must bereinspected till it passes.

Certified technicians must pass a comprehen-sive examination on emissions control, gas analysis,diagnosing, electronics and engine management forgasoline engines. Diesel and alternate fuel examina-tions may be taken at the same time.

Older vehicles typically account for a high per-centage of failed vehicles. Later vehicles, especially ifequipped with OBD II on-board diagnostics, accountfor a very low percentage of failures; 2005 vehiclesare 98% cleaner than 1970 vehicles.

Because of this, Ontario plans to phase out theDrive Clean program by 2008;AirCare is consideringtesting older vehicles only, starting in 2006.

ADVANCED VEHICLES

The Road to Zero Emissions

In 1990, the California Air Resources Board (CARB)adopted a requirement that 10% of the new cars of-fered for sale in California from 2003 on would haveto be zero emission vehicles (ZEV): cars and trucksthat produce no evaporative or exhaust emissions.

This was later reduced to 4% ZEVs, provided theremaining 6% are clean enough to qualify as partialZEVs. The 4% ZEV level may be further reduced to2% in the future.

726 CHAPTER 30

Emission Control Device Operation, Diagnosis, and Service 727

Figure 30–33 Emissions testing procedure. (Reprinted with permission from Pacific Vehicle Testing Technologies Ltd.,operators of the BC AirCare Program. All rights reserved.)

728 CHAPTER 30

Figure 30–34 Vehicle emission inspection report. (Reprinted with permission from Pacific Vehicle Testing TechnologiesLtd., operators of the BC AirCare Program. All rights reserved.)

18-FEB-2004

7121374

ppm 89.00 5.00 13.50 PASS

ppm 1007 364.00 259.50 PASS

% 0.68 0.00 0.03 PASS

ppm 107

-Your vehicle has passed.-This report may be necessary when licensing this vehicle.

2 8 PASS

% 0.81 0.00 0.02 PASS

1991 TOYT 1385 JT2VV22F3M 15-FEB-2005LDGV 2.5 71

15:36:18 $23.00 PASS PASS PASS PASS PASS

Electric Vehicles

Battery-powered electric vehicles were the firstchoice of most automakers to meet the new ZEVrules. Electric motors produce maximum power at 0rpm and work well for around town transportation.The downside is a limited driving range of 80 to 160km (50 to 100 mi), time for battery recharging, andthe space required for a very heavy battery pack.

As an example, the Ford Ranger EV pickup truck(see Figure 30–36) has 39 8 volt lead-acid batterymodules that weigh almost 900 kg (2000 lb). Con-nected in series, the battery pack produces over300 volts to power the drive motor. See Figure 30–37.Switching to very expensive nickel-metal hydridebatteries (25 12-volt modules) reduced the batterypack weight to 590 kg (1300 lb) and increased thedriving range from 80 km (50 mi) to 130 km (80 mi).The Ranger was the only major EV imported intoCanada. It is now discontinued.

By the year 2000, DaimlerChrysler, Ford, G.M.,Honda, Nissan, and Toyota were all manufacturingelectric vehicles. This ended shortly after for a num-ber of reasons: relaxed CARB ZEV rules, low con-sumer demand, high initial costs, and concerns thatZEVs are not really zero emission vehicles, as emis-sions are often generated at the power company pro-ducing electricity to charge the batteries. These arecalled indirect emissions.

Hybrid Vehicles

Hybrids are the combination of a gasoline internalcombustion engine and an electric motor. A smallergasoline engine, which increases fuel economy andlowers emissions, can then be used; the electric motorpower is brought in during high load conditions. Thetotal power of the engine and the motor cannot beadded together, as gasoline engines produce maximum

Emission Control Device Operation, Diagnosis, and Service 729

Figure 30–35. (a) Typical enhanced exhaust emission testing facility. The sign says to leave the engine running. (b) Vehiclebeing “driven” on the dynamometer. The driver is following a trace displayed on a television screen. (c) The gas cap is testedfor leakage. (d) The final report is printed and given to the driver.

(a)

(b)

(c)

(d)

power at higher RPM, while electric motors producemaximum power at 0 rpm. See Figure 30–38.

Series and Parallel Hybrids

Series hybrids use the engine to drive a generator,which in turn powers an electric motor that drives thewheels. Parallel hybrids use both the engine and theelectric motor to propel the vehicle. See Figure 30–39.

Extensive Testing

Both Honda and Toyota carried out extensive testingin Japan before releasing the cars for sale in Canada

and the U.S. Almost 50 000 hybrids were sold inJapan during the three years prior to North Ameri-can introduction.

Honda Insight and Civic

Honda calls their system Integrated Motor Assist(IMA). The Insight uses a small 1.0-litre, 3-cylinderaluminum engine as the main power source; an elec-tric motor mounted in the bell housing supplies ad-ditional power assist during high load conditionsand acceleration. See Figures 30–40 and 30–41. Theelectric motor also functions as a generator duringbraking and deceleration to keep the 144 volt NiMH

730 CHAPTER 30

Figure 30–37 A typical motor/transaxle unit; torque is controlled by varying the amount ofcurrent flowing through the stator. The motor also charges (regenerates) the battery packduring braking. (Courtesy Ford Motor Co.)

Figure 30–36 A Ford Ranger electric truck uses 39 batteries mounted under the pickup bed.(Courtesy Ford Motor Co.)

Emission Control Device Operation, Diagnosis, and Service 731

100

80

Torque(lb/ft)

2000 4000

Output(Hp)

80

60

40

20

91

66

67

73

6000

Engine speed (rpm)

8000

60

Motor assistance

Figure 30–39 Series and parallel hybrid systems. (Courtesy Honda Canada Inc.)

Figure 30–38 Combined power output of aHonda Integrated Motor Assist (IMA) hybrid.Note the electric motor produces maximumpower at low RPM and the gasoline engine athigh RPM. (Courtesy Honda Canada Inc.)

732 CHAPTER 30

Figure 30–41 The major components of the Honda IMA system are themotor, the high voltage cables, and the Intelligent Power Unit (batteriesand controls). (Courtesy Honda Canada Inc.)

Figure 30–40 The Honda Insight IMA system mounts theultra-compact electric motor in the bell housing. The motorfunctions as an assist motor, a generator and a starter.(Courtesy Honda Canada Inc.)

battery pack charged. If the battery pack shows a lowstate of charge, the motor will continue the genera-tor function at idle. No outside charging is required.

The engine will automatically shut off when com-ing to a stop unless the air conditioning is on, the bat-teries are low, or an electrical load exists (i.e., head-lights on). The IMA motor will restart the enginewhen the accelerator pedal is depressed (with theclutch disengaged). A conventional 12 volt starterand battery are used only under abnormal condi-tions, such as a low battery-module state of charge.

The Insight is a lightweight aluminum-bodied two-seater that ranks as the most fuel-efficient gasoline-powered automobile sold in North America. See Figure30–42.

The Civic is a larger four cylinder, four-seat auto-mobile that also enjoys excellent fuel economy and lowemissions. Most of the Insight IMA features also apply.

Toyota Prius

The Toyota Prius hybrid uses a slightly different con-cept. See Figures 30–43 and 30–44. Two electric mo-tors mounted in the transaxle assembly are used toboth drive the vehicle and charge the 274 volt NiMHbattery pack. See Figure 30–45. One motor (MG2)drives the wheels on acceleration and charges thebatteries during deceleration. The second motor(MG1) supplies electricity to MG2 to drive thewheels. It also functions both as a starter and a gen-erator to charge the batteries. There is no auxiliary12 volt starter. The Toyota hybrid has the ability tooperate with only the electric motor or a combinationof electric motor and engine. See Figure 30–46.

The engine stops automatically when the vehiclecomes to a stop, unless the air conditioning is on, theengine is cold, or the batteries are at a low state ofcharge. A 12 volt battery is used to power body elec-trical components and lighting.

The Prius is an extremely clean vehicle that ex-ceeds CARB super ultra-low emission vehicle(SULEV) standards for CO, HC and NOx while stillachieving excellent fuel economy and driveability.

Emission Control Device Operation, Diagnosis, and Service 733

Figure 30–43 Toyota Prius: layout of main components. (Courtesy Toyota Canada Inc.)

Engine

Inverter

Hybrid Transaxle

HV battery

Figure 30–42 The Honda Insight battery pack is mounted in the trunk area. (Courtesy Honda Canada Inc.)

734 CHAPTER 30

Figure 30–44 The Toyota Prius combines the engine, transaxleand electric motors into a single powertrain assembly.(Courtesy Toyota Canada Inc.)

Figure 30–45 The Toyota Prius uses twoelectric motors (MG1 and MG2) to drivethe wheels and charge the batteries.(Courtesy Toyota Canada Inc.)

Emission Control Device Operation, Diagnosis, and Service 735

Figure 30–46 Operating modes of the Toyota Prius hybrid. (Courtesy Toyota Canada Inc.)

Figure 30–47 Individual fuel cells are combined into astack, similar to a battery; each cell contributes to the totaloutput voltage from the stack. (Courtesy DaimlerChryslerCorporation)

SAFETY

Only trained technicians are allowed to service thehigh voltage circuits in any hybrid. Special training,insulated wearing apparel and tools are needed towork safely in this area. In 2004, as an example, Toy-ota raised their hybrid operating voltage from 274 toalmost 500 volts! Follow all safety instructions to theletter.

Industry Support

While Toyota and Honda were the first major manu-facturers to build hybrids, many other domestic andimport automakers have now joined their ranks. Fordreleased the Escape hybrid for 2005; GM joined withdiesel/hybrid transit buses in 2004 and the Silveradohybrid pickup truck in 2005. GM also plans a hybridSaturn Vue in 2006. DaimlerChrysler is currentlytesting this technology with the Dodge Durango andJeep Liberty. Asian carmakers are moving into largervehicles such as the Toyota Camry, Honda Civic, andLexus SUV.

Fuel Cell Vehicles

Very simply put, a fuel cell vehicle is an electric ve-hicle powered by an electricity generating fuel cell,rather than a battery pack.

A fuel cell is a device that produces electricity fromhydrogen (in our example), leaving nothing behind ex-cept heat and water. See Figures 30–47 and 30–48.

Fuel cells generate electricity from an electro-chemical process using hydrogen as a fuel. See Fig-ure 30–49. Compressed hydrogen is pumped into thefuel cell at the anode, the negative side of the cell.Oxygen (in the air) enters the cell from the oppositeside at the cathode, the positive side of the cell. Theoxygen attracts the hydrogen. The two are separatedby a thin electrolytic membrane of polymer material.

A platinum powder catalyst in the cell begins a re-action that strips the hydrogen of its electrons; onlythe positive charged hydrogen ions (protons) can passthrough the membrane into the positive side of thecell. This leaves the negative charged electrons be-hind. A voltage potential now exists between the two

sides of the cell. Electrons (current) flowing through acircuit (connecting the positive and negative sides)power an electric motor to drive the wheels.

The electrons (�), now at the cathode, join withthe hydrogen ions (�) and oxygen at a second plat-inum powder catalyst; a reaction occurs. Water andheat are the only products: no emissions.

When?

Almost every major automaker is developing a fuelcell vehicle. Some, such as Toyota and G.M., are us-ing their own in-house technologies; others, such asFord, DaimlerChrysler and Honda, are using fuelcells pioneered by a Canadian company, BallardPower Systems of Burnaby, British Columbia.

Many of these car companies have working proto-types currently being tested; however, full productionis still about ten years away. Reduced costs, improvedreliability, and fuel availability are concerns still to beaddressed.

736 CHAPTER 30

Figure 30–48 (a) Operation of a fuel cell.(b) Component layout. (Courtesy Ford Motor Co.)

Figure 30–49 Compressed hydrogen, stored at a hydrogen refueling station, is pumped into a fuel tank in the vehicle. It initiallyarrives at the station as either compressed hyydrogen, clean hydrocarbon fuel or natural gas. (Courtesy Toyota Canada Inc.)

Emission Control Device Operation, Diagnosis, and Service 737

PHOTO SEQUENCE 21 Testing a Vacuum-Operated EGR Valve

P21–1 A cutaway of a typical vacuum-operatedexhaust gas recirculation (EGR) valve.

P21–2 When the engine operates at idle speed, it shouldstall if the EGR valve is opened by hand. The technicianshould use a glove or shop cloth to prevent thepossibility of being burned on the hot EGR valve.

P21–3 An EGR valve can also be tested off the vehicleby applying vacuum from a hand-operated vacuumpump. The diaphragm of the valve should move whenvacuum is applied, and the vacuum should hold if thevalve is okay.

P21–4 This is a negative back-pressure EGR valve becausethe vacuum dropped to zero when shop air (compressedair) was blown over the end of the EGR valve pintle. Apositive back-pressure EGR valve would require the airpressure to close an internal valve to allow the valve toopen when vacuum was applied to the diaphragm.

P21–5 All EGR valve passages should be checked forcarbon blockages that can prevent the valve fromflowing enough exhaust gas to reduce NOx exhaustemissions.

P21–6 All EGR passages in the intake manifold shouldalso be checked for carbon and cleaned out if restricted.Use a vacuum cleaner to help get all of the pieces ofcarbon out of the passages.

738 CHAPTER 30

c. Oxides of nitrogend. Carbon dioxide

2. An air pump system with a defective one-way exhaustcheck valve could ______.

a. Create an external exhaust leakb. Cause exhaust back-pressure to decreasec. Cause the air pump to faild. Reduce engine power during cold operation

3. The charcoal canister can become saturated with gaso-line by ______.

a. Overfilling the fuel tankb. Leaking fuel injectorsc. Excessive fuel injection pressured. Leaving the gasoline filler cap loose

4. Positive back-pressure EGR valvesa. Operate at idleb. Require low exhaust back pressure to openc. Need exhaust back pressure to functiond. Operate only when the coolant temperature is

below 50°C (122°F)

5. A partially clogged EGR passage could cause the vehi-cle to fail an emissions test for ______.

a. Oxides of nitrogenb. Excessive hydrocarbonsc. Carbon monoxided. Particulates

6. Catalytic converters can be damaged bya. Long periods of idleb. Pulling a trailerc. An ignition misfired. High engine RPM

7. A good catalytic converter should bea. Hotter at the outlet than at the inletb. Hotter at the inlet than at the outlet

8. Smog is formed in the atmosphere when oxides of ni-trogen combine with ______.

a. Carbon monoxideb. Hydrocarbonsc. Carbon dioxided. Particulate matter

9. Diesel engines are tested with an opacity meter thatpasses a light beam through the exhaust gases at thetailpipe. This measures

a. Exhaust volumeb. Exhaust densityc. Carbon monoxide levelsd. Excessive back pressure

10. Hybrid vehicles reduce total exhaust emission becausea. The engines are very efficientb. They only carry two passengersc. The batteries are charged overnightd. A smaller internal combustion engine can be

used

SUMMARY

1. The positive crankcase ventilation (PCV) system pullsblow-by gases and crankcase vapours into the intakemanifold.

2. The PCV valve allows a metered amount of manifoldvacuum to be applied to the crankcase. The valve canbe tested by rattling the valve or by using a card overthe oil fill opening.

3. An AIR pump supplies air to the exhaust manifoldwhen the engine is cold and to the catalytic converterwhen the engine achieves closed-loop operation.

4. The evaporative emission control (EVAP) system usesa charcoal (carbon) canister and various hoses andlines to trap and hold gasoline fumes and to preventthese fumes from escaping into the atmosphere.

5. The exhaust gas recirculation (EGR) system bleedssome inert exhaust gases into the combustion cham-ber to prevent the higher peak temperature that couldoccur. The main purpose and function of the EGR sys-tem is to reduce the formation of oxides of nitrogen(NOx) exhaust emissions.

6. A catalytic converter is used in the exhaust system tostart a chemical reaction among the exhaust gases butthe catalysts are not consumed by the reaction. Itsfunction is to separate NOx exhaust emissions into ni-trogen (N) and oxygen (O2). The other part of the con-verter is designed to oxidize hydrocarbons (HC) andcarbon monoxides (CO) into harmless CO2 and H2O(water vapour).

7. Hybrid vehicles use a combination of a smaller inter-nal combustion engine and an electric drive motor.Fuel cells convert hydrogen gas into electricity topower an electric drive motor.

REVIEW QUESTIONS

1. List three tests that can be performed to check the PCVsystem.

2. Describe how to test an AIR system using an exhaustgas analyzer.

3. Explain how to perform a pressure test on an evapora-tive control system.

4. List three methods that can be used to test an EGRvalve and system.

5. Describe three tests that can be used to test the condi-tion of a catalytic converter.

RED SEAL CERTIFICATION-TYPE QUESTIONS

1. Positive crankcase ventilation (PCV) systems help tocontrol ______.

a. Particulatesb. Hydrocarbons