Halderman J.D., Linder J. Automotive Fuel and Emissions Control Systems

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CATALYTIC CONVERTERS 351

STEP BY STEP

The CO molecule is absorbed onto a catalyst side. Only

a few grams of catalyst material are applied to the

washcoat.

The CO molecule is converted to a CO

molecule.

The CO

molecule is exiting the small micropore.

The CO

molecule is exiting the larger micropore.

The CO

molecule is exiting the converter.

A poisoned converter.

CATALYST

MATERIAL

CATALYST

MATERIAL

CATALYST

MATERIAL

MICROPORE

POISON

MACROPORE

POISON

POROUS

WASHCOAT

352 CHAPTER 28

5. A catalytic converter has to be over 500°F (260°C) before

it starts to become effective and is therefore mounted as

close as possible to the exhaust parts of the engine.

6. The OBD-II system monitor compares the relative activity

of a rear oxygen sensor to the precatalytic oxygen sensor

to determine catalytic converter efficiency.

7. Catalytic converters can be tested for restriction and for

efficiency.

1. A catalytic converter is an after treatment device that

reduces exhaust emissions outside of the engine.

2. The honeycomb shape of the catalytic converter is con-

structed of a ceramic material about 0.006 inch thick with

small square openings.

3. A catalyst is an element that starts a chemical reaction but

is not consumed in the process.

4. The catalyst materials used in a catalytic converter include

rhodium, palladium, and platinum.

SUMMARY

4. How does the computer monitor catalytic converter

performance?

5. What tests can be performed by a service technician to

test the catalytic converter?

1. What are the three most commonly used catalysts in a

catalytic converter?

2. How does a catalytic converter reduce NO

to nitrogen and

oxygen?

3. Why must a catalytic converter be mounted close to the

exhaust ports of the engine?

REVIEW QUESTIONS

5. A catalytic converter can be harmed by ______________ .

a. Excessive engine oil

b. Antifreeze

c. Sulfur from poor-quality fuel

d. Any of the above

6. Two technicians are discussing testing a catalytic con-

verter. Technician A says that a vacuum gauge can be

used and observed to see if the vacuum drops with the

engine at 2,500 RPM for 60 seconds. Technician B says

that a pressure gauge can be used to check for back pres-

sure. Which technician is correct?

a. Technician A only

b. Technician B only

c. Both Technicians A and B

d. Neither Technician A nor B

7. A catalytic converter is being tested with an infrared py-

rometer. Which is an acceptable (good converter) result?

a. The inlet should be hotter than the outlet by 10%.

b. The outlet should be hotter than the inlet by 10%.

c. Both the inlet and the outlet should be the same

temperature after the converter reaches operating

temperature.

d. The temperature of a catalytic converter is the best

test to perform to locate a restricted (clogged) unit.

1. What is applied to the ceramic substrate to make the sur-

face porous?

a. Honeycomb filler

b. Washcoat

c. Aluminum

d. Cerium

2. Two technicians are discussing catalytic converters. Tech-

nician A says that the exhaust mixture must fluctuate

between rich and lean for the best efficiency. Technician

B says that the air-fuel mixture must be leaner than 14.7:1

for best performance from a three-way catalytic converter.

Which technician is correct?

a. Technician A only

b. Technician B only

c. Both Technicians A and B

d. Neither Technician A nor B

3. A catalytic converter has to be at least how hot before it

starts to work?

a. 500°F (260°C)

b. 1,000°F (540°C)

c. 1,500°F (815°C)

d. 2,000°F (1,100°C)

4. What two primary sensors does the PCM use to check the

catalytic converter?

a. Catalytic converter temperature sensor and rear

oxygen sensor

b. Precat and postcat oxygen sensor

c. Precat oxygen sensor and MAF

d. MAP and TP

CHAPTER QUIZ

CATALYTIC CONVERTERS 353

10. Technician A says that the catalytic converter is warranted

for eight years or 80,000 miles, whichever comes first.

Technician B says that after replacing the catalytic con-

verter, the old converter must be kept for possible inspec-

tion for 60 days. Which technician is correct?

a. Technician A only

b. Technician B only

c. Both Technicians A and B

d. Neither Technician A nor B

8. Which exhaust gas reading indicates a good catalytic

converter?

a. O

is zero c. Both a and b

b. CO is zero d. Neither a nor b

9. A P0422 (catalytic converter efficiency failure) is set. What

is a possible cause?

a. Engine mechanical fault

b. Exhaust leak

c. Fuel contamination

d. Any of the above

354 CHAPTER 29

chapter

IGNITION SYSTEM

OPERATION

AND DIAGNOSIS

OBJECTIVES: After studying Chapter 29 , the reader should be able to: • Prepare for ASE Engine Performance (A8)

certification test content area “B” (Ignition System Diagnosis and Repair). • Explain how ignition coils create 40,000 volts or

more. • Discuss crankshaft position sensor and pickup coil operation. • Describe the operation of waste-spark

and coil-on-plug (COP) ignition systems. • Describe how to test ignition coils. • Explain how to test spark plug wire.

• Describe the test procedure for the diagnosis and repair of electronic ignition systems. • Explain how to inspect

and replace spark plugs. • Discuss what to inspect and look for during a visual inspection of the ignition system. • List the

steps necessary to check and/or adjust ignition timing on engines equipped with a distributor-type ignition system.

KEY TERMS: Coil-on-plug (COP) ignition 355 • Companion cylinders 361 • Detonation 365 • Distributor ignition 355

• Electronic ignition 355 • EMI 355 • Firing order 360 • Hall effect 357 • ICM 356 • Ignition coil 355 • Ignition

timing 375 • Ion-sensing ignition 365 • Iridium spark plugs 372 • Knock sensors 365 • Magnetic pulse generator 357

• Pickup coil 357

• Ping 365 • Platinum spark plugs 372 • Primary ignition circuit 356 • Primary winding 355 • Schmitt

trigger 358 • Secondary ignition circuit 356 • Secondary winding 355 • Spark knock 365

• Spark plugs 372 • Spark

tester 367 • Switching 356 • Track 370 • Transistor 357 • Trigger 357 • Turns ratio 355 • Waste-spark system 355

PURPOSE AND FUNCTION The ignition system includes

components and wiring necessary to create and distribute a high

voltage (up to 40,000 volts or more) and send to the spark plug.

Ahigh-voltage arc occurs across the gap of a spark plug at the

right time inside the combustion chamber. The spark raises the

temperature of the air-fuel mixture and starts the combustion

process inside the cylinder.

BACKGROUND All ignition systems apply battery voltage

(close to 12 volts) to the positive side of the ignition coil(s) and

pulse the negative side to ground:



Early ignition systems. Before the mid-1970s, ignition

systems used a mechanically opened set of contact

points to make and break the electrical connection to

ground. Acam lobe, located in and driven by the distribu-

tor, opened the points. There was one lobe for each cylin-

der. The points used a rubbing block that was lubricated

by applying a thin layer of grease on the cam lobe at

each service interval. Each time the points opened, a high

voltage was created in the ignition coil. The high-voltage

then traveled to each spark plug through the distributor

cap and rotor. The distributor was used twice in the

creation of the spark, as follows:

IGNITION SYSTEM

POINTS

DISTRIBUTOR

CAM

CONDENSER

FIGURE 29–1 A point-type distributor from a hot rod.

1. It was connected to the camshaft which rotated the

distributor cam, causing the points to open and close.

2. It used a rotor to send the high-voltage from the coil

entering the center of the distributor cap to inserts

connected to spark plug wires to each cylinder.

 SEE FIGURE 29–1 .



Electronic ignition. Since the mid-1970s, ignition sys-

tems have used sensors, such as a pickup coil and

reluctor (trigger wheel), to trigger or signal an electronic

module that switches the primary ground circuit of the

IGNITION SYSTEM OPERATION AND DIAGNOSIS 355

ignition coil. Distributor ignition is the term specified by

the Society of Automotive Engineers (SAE) for an ignition

system that uses a distributor. Electronic ignition is the

term specified by the SAE for an ignition system that does

not use a distributor. Electronic ignition system types

include the following:

1. Waste-spark system. This type of system uses one

ignition coil to fire the spark plugs for two cylinders at

the same time.

2. Coil-on-plug (COP) system. This type of system uses

a single ignition coil for each cylinder with the coil

placed above or near the spark plug.

IGNITION COIL CONSTRUCTION The heart of any igni-

tion system is the ignition coil. When the coil negative lead is

grounded, the primary (low-voltage) circuit of the coil is com-

plete, and a magnetic field is created around the coil windings.

When the circuit is opened, the magnetic field collapses and

induces a high voltage in the secondary winding of the igni-

tioncoil.

The coil creates a high-voltage spark by electromagnetic

induction. Many ignition coils contain two separate but electri-

cally connected windings of copper wire. Other coils are true

transformers in which the primary and secondary windings are

not electrically connected.

 SEE FIGURE 29–2 .

The center of an ignition coil contains a core of laminated

soft iron (thin strips of soft iron). This core increases the mag-

netic strength of the coil:



Secondary coil winding. Surrounding the laminated

core are approximately 20,000 turns of fine wire (approxi-

mately 42 gauge). The winding is called the secondary

winding.



Primary coil winding. Surrounding the secondary

windings are approximately 150 turns of heavy wire

(approximately 21 gauge). The winding is called the

primary winding. The secondary winding has about

100times the number of turns of the primary winding,

referred to as the turns ratio (approximately 100:1).

In older coils, these windings are surrounded with a thin

metal shield and insulating paper and placed into a metal

container filled with transformer oil to help cool the coil wind-

ings. Other coil designs use an air-cooled, epoxy-sealed

E coil. The E coil is so named because the laminated, soft iron

core is E shaped, with the coil wire turns wrapped around

the center “finger” of the E and the primary winding wrapped

inside the secondary winding.

 SEE FIGURES 29–3

AND 29–4.

IGNITION COIL OPERATION All ignition systems use

electromagnetic induction to produce a high-voltage spark from

the ignition coil. Electromagnetic induction (EMI) means that

a current can be created in a conductor (coil winding) by a

moving magnetic field. The magnetic field in an ignition coil is

produced by current flowing through the primary winding of

BATTERY (B+)

IGNITION

SWITCH

IGNITION

SWITCH

PRIMARY

SECONDARY

COIL

IGNITION

MODULE

SPARK

PLUG

BATTERY (B+)

PRIMARY

SECONDARY

COIL

IGNITION

MODULE

SPARK

PLUG

SPARK

PLUG

FIGURE 29–2 Some ignition coils are electrically connected,

called married (top figure), whereas others use separate pri-

mary and secondary windings, called divorced (lower figure).

The polarity (positive or negative) of a coil is determined by the

direction in which the coil is wound.

FIGURE 29–3 The steel lamination used in an E coil helps

increase the magnetic field strength, which helps the coil pro-

duce higher energy output for a more complete combustion in

the cylinders.

356 CHAPTER 29

the coil. An ignition coil is able to increase battery voltage to

40,000 volts or more in the following way:



Battery voltage is applied to the primary winding.



A ground is provided to the primary winding by the

ignition control module (ICM), igniter, or PCM.



Current (approximately 2 to 6 amperes) flows in the primary

coil creating a magnetic field in the primary winding.



When the ground is opened by the ICM, the built-up

magnetic field collapses.



The movement of the collapsing magnetic field

induces a voltage of 250 to 400 volts in the primary

winding and 20,000 to 40,000 volts or more in the

secondary winding with a current of 0.020 to

0.080ampere.



The high voltage created in the secondary winding is high

enough to jump the air gap at the spark plug.



The electrical arc at the spark plug ignites the air-fuel

mixture in the combustion chamber of the engine.



For each spark that occurs, the coil must be charged with

a magnetic field and then discharged.

SECONDARY

TERMINAL

PRIMARY

WINDING

SECONDARY

WINDING

FIGURE 29–4 The primary windings are inside the secondary

windings on this General Motors coil.

ICM

SECONDARY

PRIMARY

IGNITION

SWITCH

COIL

CMP

SENSOR

CKP

SENSOR

PCM

FIGURE 29–5 The primary ignition system is used to trigger

and therefore create the secondary (high-voltage) spark from

the ignition coil.

The spark from an ignition coil is strong enough

to cause physical injury. Always follow the exact

service procedure and avoid placing hands near

the secondary ignition components when the

engine is running.

WARNING

The ignition components that regulate the current in the

coil primary winding by turning it on and off are known collec-

tively as the primary ignition circuit. When the primary circuit

is carrying current, the secondary circuit is off. When the pri-

mary circuit is turned off, the secondary circuit has high volt-

age. The components necessary to create and distribute the

high voltage produced in the secondary windings of the coil are

called the secondary ignition circuit.

 SEE FIGURE 29–5 .

These circuits include the following components:



Primary ignition circuit

1. Battery

2. Ignition switch

3. Primary windings of coil

4. Pickup coil (crankshaft position sensor)

5. Ignition control module (igniter)



Secondary ignition circuit

1. Secondary windings of coil

2. Distributor cap and rotor (if the vehicle is so equipped)

3. Spark plug wires

4. Spark plugs

IGNITION SWITCHING

AND TRIGGERING

SWITCHING For any ignition system to function, the primary

current must be turned on to charge the coil and off to allow the

coil to discharge, creating a high-voltage spark. This turning on

and off of the primary circuit is called switching. The unit that does

IGNITION SYSTEM OPERATION AND DIAGNOSIS 357

NARROW GAP

RESULTS IN

STRONG MAGNETIC

FIELD FOR COIL

ROTATING FERROUS

METAL RELUCTOR

PERMANENT

MAGNET

WIDE GAP

OFFERS WEAK

MAGNETIC

FIELD FOR

COIL

PERMANENT

MAGNET

VOLTAGE REVERSES AS STAR WHEEL

MOVES PAST CLOSEST POINT





FIGURE 29–6 Operation of a typical pulse generator (pickup coil). At the bottom is a line drawing of a typical scope pattern

ofthe output voltage of a pickup coil. The module receives this voltage from the pickup coil and opens the ground circuit to the

ignition coil when the voltage starts down from its peak (just as the reluctor teeth start moving away from the pickup coil).

triggers the transistor inside the module and is also used by

the PCM for piston position information and engine speed

(RPM). The reluctor is shaped so that the magnetic strength

changes enough to create a usable varying signal for use by

the module to trigger the coil.

 SEE FIGURE 29–6 .

Magnetic crankshaft position sensors use the changing

strength of the magnetic field surrounding a coil of wire to

signal the module and computer. This signal is used by the

electronics in the module and computer to determine piston

position and engine speed (RPM). This sensor operates simi-

larly to the distributor magnetic pickup coil. The crankshaft

position sensor uses the strength of the magnetic field sur-

rounding a coil of wire to signal the ICM. The rotating crank-

shaft has notches cut into it that trigger the magnetic position

sensor, which change the strength of the magnetic field as the

notches pass by the position sensor.

 SEE FIGURE 29–7 .



Hall-effect switch. This switch also uses a stationary sen-

sor and rotating trigger wheel (shutter). Unlike the magnetic

pulse generator, the Hall-effect switch requires a small input

voltage to generate an output or signal voltage. Hall effect

has the ability to generate a voltage signal in semiconduc-

tor material (gallium arsenate crystal) by passing current

through it in one direction and applying a magnetic field to

it at a right angle to its surface. If the input current is held

steady and the magnetic field fluctuates, an output voltage

is produced that changes in proportion to field strength.

Most Hall-effect switches in distributors have the following:

1. Hall element or device

2. Permanent magnet

3. Rotating ring of metal blades (shutters) similar to a trig-

ger wheel (Another method uses a stationary sensor

with a rotating magnet.)

 SEE FIGURE 29–8 .

the switching is an electronic switch, such as a power transistor.

This power transistor can be found in the following locations:



Ignition control module (ICM) or igniter



PCM (computer)

NOTE: On some coil-on-plug (COP) systems, the ICM is part

of the ignition coil itself and is serviced as an assembly.

TRIGGERING The device that signals the switching of the

coil on and off or just on in most instances is called the trigger.

A trigger is typically a pickup coil in some distributor-type

ignitions and a crankshaft position sensor (CKP) on electronic

systems (waste spark and coil on plug). There are three types of

devices used for triggering:

1. Magnetic sensor

2. Hall-effect switch

3. Optical sensor

PRIMARY CIRCUIT OPERATION To get a spark out of

an ignition coil, the primary coil circuit must be turned on and off.

The primary circuit current switching is controlled by a transistor

(electronic switch) inside the ignition module (or igniter) or PCM

and is controlled by one of several devices, including the following:



Magnetic sensor. A simple and common ignition electronic

switching device is the magnetic pulse generator system.

This is a type of magnetic sensor, often called a magnetic

pulse generator or pickup coil, and is installed in the dis-

tributor housing. The pulse generator consists of a trigger

wheel (reluctor) and a pickup coil. The pickup coil consists of

an iron core wrapped with fine wire, in a coil at one end and

attached to a permanent magnet at the other end. The center

of the coil is called the pole piece. The pickup coil signal

358 CHAPTER 29

Some blades are designed to hang down, typically

found in Bosch and Chrysler systems, while others may

be on a separate ring on the distributor shaft, typically

found in General Motors and Ford Hall-effect distributors.

There are two types of Hall effect sensors used, including

the following:



When the shutter blade enters the gap between

the magnet and the Hall element, it creates a

magnetic shunt that changes the field strength

through the Hall element.



This analog signal is sent to a Schmitt trigger

inside the sensor itself, which converts the analog

signal into a digital signal. A digital (on or off) volt-

age signal is created at a varying frequency to the

ignition module or onboard computer.

 SEE

FIGURE 29–9 .



Optical sensors. These use light from an LED and

a phototransistor to signal the computer. An inter-

rupter disc between the LED and the phototransis-

tor has slits that allow the light from the LED to

trigger the phototransistor on the other side of the

disc. Most optical sensors (usually located inside

the distributor) use two rows of slits to provide

individual cylinder recognition (low resolution) and

precise distributor angle recognition (high reso-

lution) signals that are used for cylinder misfire

detection.

 SEE FIGURE 29–10 on page 360.

MAXIMUM

POSITIVE

SWING









MAXIMUM

NEGATIVE

SWING

SWINGS

THROUGH

ZERO VOLTS

















FIGURE 29–7 A magnetic sensor uses a permanent magnet

surrounded by a coil of wire. The notches of the crankshaft (or

camshaft) creates a variable magnetic field strength around

the coil and create an analog signal when the engine rotates.

When a metallic section is close to the sensor, the magnetic

field is stronger because metal is a better conductor of mag-

netic lines of force than air.

Optical Distributors Do Not Like Light

Optical distributors use the light emitted from LEDs

to trigger phototransistors. Most optical distributors

use a shield between the distributor rotor and the

optical interrupter ring. Sparks jump the gap from

the rotor tip to the distributor cap inserts. This shield

blocks the light from the electrical arc from interfer-

ing with the detection of the light from the LEDs.

If this shield is not replaced during service, the

light signals are reduced, and the engine may not

operate correctly.

 SEE FIGURE 29–11 on page 360.

This can be difficult to detect because nothing

looks wrong during a visual inspection. Remember

that all optical distributors must be shielded between

the rotor and the interrupter ring.

TECH TIP

The Tachometer Trick

When diagnosing a no-start or intermediate missing

condition, check the operation of the tachometer. If the

tachometer does not indicate engine speed (no-start

condition) or drops toward zero (engine missing), then

the problem is due to a defect in the primary ignition

circuit. The tachometer gets its signal from the pulsing

of the primary winding of the ignition coil. The follow-

ing components in the primary circuit could cause the

tachometer to not work when the engine is cranking:

• Pickup coil

• Crankshaft position sensor

• Ignition module (igniter)

• Coil primary wiring

If the vehicle is not equipped with a tachometer,

use a scan tool to look at engine RPM. The results

are as follows:

• No or an unstable engine RPM reading means the

problem is in the primary ignition circuit.

• A steady engine RPM reading means the

problemis in the secondary ignition circuit or is a

fuel-related problem.

TECH TIP

359

1 KΩ

+5 V

SIGNAL

GROUND

0 V

+5 V

TRIGGER

WHEEL

HALL-EFFECT

SENSOR

FIGURE 29–8 A Hall-effect sensor produces a digital on-off voltage signal whether it is used with a blade or a notched wheel.

HALL-EFFECT REFERENCE

CAMSHAFT SENSOR

REFERENCE

FOR CYLINDER #5

REFERENCE

FOR CYLINDER #4

REFERENCE

FOR CYLINDER #6

REFERENCE

FOR CYLINDER #3

REFERENCE

FOR CYLINDER #2

REFERENCE FOR CYLINDER #1

HALL-EFFECT CRANKSHAFT

POSITION SENSOR

TORQUE CONVERTER

DRIVE PLATE

CRANK SENSOR

ELECTRICAL

CONNECTOR

PAPER

SPACER

CAM SENSOR

ELECTRICAL

CONNECTOR

CRANK

CAM

TDC-2

O-RING

TDC-3 TDC-4

TDC-5

TDC-6 TDC-1

PAPER

SPACER

SLOTS

FIGURE 29–9 Some Hall-effect sensors look like magnetic sensors. This Hall-effect camshaft reference sensor and

crankshaft position sensor have an electronic circuit built in that creates a 0- to 5-volt signal as shown at the bottom. These

Hall-effect sensors have three wires: a power supply (8 volts) from the computer (controller), a signal (0 to 5 volts), and a

signal ground.

360 CHAPTER 29

ROTOR PLATE

CRANK ANGLE

SENSOR

ROTOR SHAFT

(a)

FIGURE 29–10 (a) Typical optical distributor. (b) Cylinder I slit signals the computer the piston position for cylinder I. The

1-degree slits provide accurate engine speed information to the PCM. Optical sensors generate digital (on and off) signals.

(b)

ROTOR PLATE

180° SIGNAL SLIT FOR NO. 1 CYLINDER

180°

SIGNAL SLIT

1° SIGNAL SLIT

FIGURE 29–11 A light shield is being installed on an optical

distributor before the rotor is attached.

FIGURE 29–12 The firing order is cast or stamped on the in-

take manifold on most engines that have a distributor ignition.



First, to trigger the ignition control module by the use of

the rotating distributor shaft



Second, by rotating the rotor to distribute the high-

voltage spark to the individual spark plugs

FIRING ORDER Firing order means the order that the

spark is distributed to the correct spark plug at the right

time. The firing order of an engine is determined by crank-

shaft and camshaft design. The firing order is determined

by the location of the spark plug wires in the distributor cap

of an engine equipped with a distributor. The firing order is

often cast into the intake manifold for easy reference.

 SEE

FIGURE 29–12 .

Service information also shows the firing order and the di-

rection of the distributor rotor rotation as well as the location of

the spark plug wires on the distributor cap.

PURPOSE AND FUNCTION The purpose of a distributor

is to distribute the high-voltage spark from the output terminal

of the ignition coil to the spark plugs for each cylinder. A gear

or shaft drives the distributor that is connected to the camshaft

and is driven at camshaft speed. Most distributor ignition sys-

tems also use a sensor to trigger the ignition control module.

OPERATION OF DISTRIBUTOR IGNITION The distrib-

utor is used twice in most ignition systems that use a distributor:

DISTRIBUTOR

IGNITION