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

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IGNITION SYSTEM OPERATION AND DIAGNOSIS 371

FIGURE 29–29 Corroded terminals on a waste-spark coil

can cause misfire diagnostic trouble codes to be set.

FIGURE 29–30 This spark plug boot on an overhead

camshaft engine has been arcing to the valve cover causing

amisfire to occur.

FIGURE 29–31 Measuring the resistance of a spark plug

wire with a multimeter set to the ohms position. The reading

of 16.03 kΩ (16,030 ohms) is okay because the wire is about

2feet long. Maximum allowable resistance for a spark plug

wire this long would be 20 kΩ (20,000 ohms).

FIGURE 29–32 This spark plug wire boot pliers is a handy

addition to any tool box.

Spark Plug Wire Pliers Are a Good Investment

Spark plug wires are often difficult to remove. Using

good-quality spark plug wire pliers, as shown in

 FIGURE 29–32 , saves time and reduces the

chance of harming the wire during removal.

TECH TIP

Route the Wires Right!

High voltage is present through spark plug wires

when the engine is running. Surrounding the spark

plug wires is a magnetic field that can affect other

circuits or components of the vehicle. For exam-

ple, if a spark plug wire is routed too closely to

the signal wire from a mass airflow (MAF) sensor,

the induced signal from the ignition wire could

create a false MAF signal to the computer. The

computer, not able to detect that the signal was

false, would act on the MAF signal and command

the appropriate amount of fuel based on the false

MAF signal.

To prevent any problems associated with high-

voltage spark plug wires, be sure to route them using

all of the factory holding brackets and wiring combs.

 SEE FIGURE 29–33 .

If the factory method is unknown, most factory

service information shows the correct routing.

TECH TIP

372 CHAPTER 29

in diameter. The small diameter reduces the voltage required to

jump the gap between the center and the side electrode, thereby

reducing possible misfires. The ground or side electrode is usu-

ally tipped with platinum to help reduce electrode gap wear.

Spark plugs should be inspected when an engine perfor-

mance problem occurs and should be replaced at specified in-

tervals to ensure proper ignition system performance:



Nonplatinum spark plugs have a service life of over

20,000 miles (32,000 km).



Platinum-tipped original equipment spark plugs have a

typical service life of 60,000 to 100,000 miles (100,000 to

160,000 km) or longer.

Used spark plugs should not be cleaned and reused un-

less absolutely necessary. The labor required to remove and

replace (R & R) spark plugs is the same whether the spark plugs

are replaced or cleaned. Although cleaning spark plugs often

restores proper engine operation, the service life of cleaned

spark plugs is definitely shorter than that of new spark plugs.

FIGURE 29–33 Always take the time to install spark plug

wires back into the original holding brackets (wiring combs).

CERAMIC

INSULATOR

METAL SHELL

INSULATION

CENTER

ELECTRODE

SIDE

ELECTRODE

THREADS

METAL

SHELL

FIGURE 29–34 Parts of a spark plug.

FAST

HEAT

TRANSFER

MEDIUM

HEAT

TRANSFER

SLOW

HEAT

TRANSFER

COLD PLUG

HOT PLUG

FIGURE 29–35 The heat range of a spark plug is determined

by distance the heat flows from the tip to the cylinder head.

SPARK PLUG CONSTRUCTION Spark plugs are manu-

factured from ceramic insulators inside a steel shell. The threads

of the shell are rolled and a seat is formed to create a gastight

seal with the cylinder head.

 SEE FIGURE 29–34 .

The physical differences in spark plugs include the following:



Reach. This is the length of the threaded part of the plug.



Heat range. This refers to how rapidly the heat created

at the tip is transferred to the cylinder head. A spark plug

with a long ceramic insulator path will run hotter at the tip

than one that has a shorter path because the heat must

travel farther.

 SEE FIGURE 29–35 .



Type of seat. Some spark plugs use a gasket, and others

rely on a tapered seat to seal.

RESISTOR SPARK PLUGS Most spark plugs include a

resistor in the center electrode, which helps to reduce electro-

magnetic noise or radiation from the ignition system. The closer

the resistor is to the actual spark or arc, the more effective it

becomes. The value of the resistor is usually between 2,500

and 7,500 ohms.

PLATINUM SPARK PLUGS Platinum spark plugs have

a small amount of the precious metal platinum included on the

end of the center electrode as well as on the ground or side

electrode. Platinum is a gray-white metal that does not react

with oxygen and, therefore, will not erode away as can occur

with conventional nickel alloy spark plug electrodes. Platinum is

also used as a catalyst in catalytic converters, where it is able to

start a chemical reaction without itself being consumed.

IRIDIUM SPARK PLUGS Iridium is a white precious metal

and is the most corrosion-resistant metal known. Most iridium

spark plugs use a small amount of iridium welded onto the tip

of a small center electrode, 0.0015 to 0.002 inch (0.4 to 0.6 mm)

SPARK PLUGS

IGNITION SYSTEM OPERATION AND DIAGNOSIS 373

NOTE: Platinum-tipped spark plugs should not be re-

gapped on one that has been used in an engine be-

fore. The engine heat makes the platinum brittle, and

the center electrode can be easily broken if regapping

the plug is attempted. Using a gapping tool can break

the platinum after it has been used in an engine. Check

service information regarding the recommended type of

spark plugs and the specified service procedures.

SPARK PLUG SERVICE When replacing spark plugs, per-

form the following steps:

STEP 1 Check service information. Check for the exact

spark plug to use and the specified instructions and/

or technical service bulletins that affect the number of

plug to be used or a revised replacement procedure.

STEP 2 Allow the engine to cool before removing spark

plugs. This is true especially on engines with alumi-

num cylinder heads.

STEP 3 Use compressed air or a brush to remove dirt from

around the spark plug before removal. This step

helps prevent dirt from getting into the cylinder of an

engine while removing a spark.

STEP 4 Check the spark plug gap and correct as needed.

Be careful not to damage the tip on the center electrode

if adjusting a platinum or iridium type of spark plug.

STEP 5 Install the spark plugs by hand. After tightening by

hand, use a torque wrench and tighten the spark plugs

to factory specifications.

 SEE FIGURES 29–36 AND

29–37 .

Spark plugs are the windows to the inside of the combustion

chamber. A thorough visual inspection of the spark plugs often

can lead to the root cause of an engine performance problem.

Two indications on spark plugs and their possible root causes

in engine performance include the following:

1. Carbon fouling. If the spark plug(s) has dry black carbon

(soot), the usual causes include the following:



Excessive idling



Overly rich air-fuel mixture due to a fuel system fault



Weak ignition system output

2. Oil fouling. If the spark plug has wet, oily deposits with lit-

tle electrode wear, oil may be getting into the combustion

chamber from the following:



Worn or broken piston rings



Worn valve guides



Defective or missing valve stem seals

When removing spark plugs, place them in order so that

they can be inspected to check for engine problems that might af-

fect one or more cylinders. All spark plugs should be in the same

condition, and the color of the center insulator should be light tan

or gray. If all the spark plugs are black or dark, the engine should

be checked for conditions that could cause an overly rich air-fuel

mixture or possible oil burning. If only one or a few spark plugs

are black, check those cylinders for proper firing (possible defec-

tive spark plug wire) or an engine condition affecting only those

particular cylinders.

 SEE FIGURES 29–38 THROUGH 29–41 .

FIGURE 29–36 When removing spark plugs, it is wise to

arrange them in the order by the cylinder they were removed

from so that they can be compared and any problem can be

identified with a particular cylinder.

FIGURE 29–37 A spark plug thread chaser is a low-cost tool

that hopefully will not be used often but is necessary to use to

clean the threads before new spark plugs are installed.

If all spark plugs are white, check for possible overad-

vanced ignition timing or a vacuum leak causing a lean air-fuel

mixture. If only one or a few spark plugs are white, check for a

vacuum leak or injector fault affecting the air-fuel mixture only

to those particular cylinders.

NOTE: The engine computer “senses” rich or lean air-

fuel ratios by means of input from the oxygen sensor(s).

If one cylinder is lean, the PCM may make all other cyl-

inders richer to compensate.

Inspect all spark plugs for wear by first checking the condi-

tion of the center electrode. As a spark plug wears, the center

electrode becomes rounded. If the center electrode is rounded,

higher ignition system voltage is required to fire the spark plug.

When installing spark plugs, always use the correct tight-

ening torque to ensure proper heat transfer from the spark plug

shell to the cylinder head.

 SEE CHART 29–1 .

NOTE: General Motors does not recommend the use of

antiseize compound on the threads of spark plugs be-

ing installed in an aluminum cylinder head because the

spark plug will be overtightened. This excessive tighten-

ing torque places the threaded portion of the spark plug

too far into the combustion chamber, where carbon can

accumulate and result in the spark plugs being difficult

to remove. If antiseize compound is used on spark plug

threads, reduce the tightening torque by 40%. Always

follow the vehicle manufacturer’s recommendations.

374

FIGURE 29–38 A normally worn spark plug that uses a

tapered platinum-tipped center electrode.

FIGURE 29–39 A worn spark plug showing fuel and/or oil

deposits.

FIGURE 29–40 A spark plug from an engine that had a

blown head gasket. The white deposits could be from the

aluminum of the piston or from the additives in the coolant.

FIGURE 29–41 A platinum tipped spark plug that is fuel

soaked indicating a fault with the fuel system or the ignition

system causing the spark plug to not fire.

IGNITION SYSTEM OPERATION AND DIAGNOSIS 375

TDC MARK

TIMING

MARK ON

HARMONIC

BALANCER

FIGURE 29–42 Ignition timing marks are found on the

harmonic balancers on engines equipped with distributors

thatcan be adjusted for timing.

or slightly before TDC (BTDC). Ignition timing changes as me-

chanical wear occurs to the following:



Timing chain



Distributor gear



Camshaft drive gear

CHECKING IGNITION TIMING To be assured of the

proper ignition timing, follow exactly the timing procedure indi-

cated on the underhood vehicle emission control information

(VECI) decal.

 SEE FIGURE 29–44 .

NOTE: The ignition timing for waste-spark and coil-on-

plug ignition systems cannot be adjusted.

CHART 29–1

Typical spark plug installation torque.



TORQUE WITH TORQUE WRENCH (LB-FT)

TORQUE WITHOUT TORQUE WRENCH

(TURNS AFTER SEATED)

SPARK PLUG TYPE CAST-IRON HEAD ALUMINUM HEAD CAST-IRON HEAD ALUMINUM HEAD

Gasket

14 mm

18 mm

26–30

32–38

18–22

28–34

1/4

Tapered seat

14 mm

18 mm

7–15

15–20

7–15

15–20

1/16 (snug)

Two-Finger Trick

To help prevent overtightening a spark plug when

a torque wrench is not available, simply use two

fingers on the ratchet handle. Even the strongest

service technician cannot overtighten a spark plug

by using two fingers.

TECH TIP

PURPOSE Ignition timing refers to when the spark plug

fires in relation to piston position. The time when the spark

occurs depends on engine speed and, therefore, must be

advanced (spark plugs fire sooner) as the engine rotates faster.

The ignition in the cylinder takes a certain amount of time, usu-

ally 30 ms (30/1,000 of a second), and remains constant regard-

less of engine speed. Therefore, to maintain the most efficient

combustion, the ignition sequence has to occur sooner as

the engine speed increases. For maximum efficiency from the

expanding gases inside the combustion chamber, the burning

of the air-fuel mixture should end by about 10 degrees after top

dead center (ATDC). If the burning of the mixture is still occur-

ring after that point, the expanding gases do not exert much

force on the piston because the gases are “chasing” the piston

as it moves downward.

Therefore, to achieve the goal of having the air-fuel mix-

ture be completely burned by the time the piston reaches

10 degrees ATDC, the spark must be advanced (occur

sooner) as the engine speed increases. This timing advance

is determined and controlled by the PCM on most vehicles.

 SEE FIGURES 29–42 AND 29–43 .

If the engine is equipped with a distributor, it may be pos-

sible to adjust the base or the initial timing. The initial timing is

usually set to fire the spark plug between zero degrees (TDC)

IGNITION TIMING

376 CHAPTER 29

1000

INITIAL TIMING

ADVANCE ANGLE BEFORE TDC

ENGINE SPEED

(

RPM

)

50004000

30002000

30°

0°

10°

20°

40°

FIGURE 29–43 The initial (base) timing is where the spark

plug fires at idle speed. The PCM then advances the timing

based primarily on engine speed.

(a)

(b)

FIGURE 29–44 (a) Typical SPOUT connector as used on many

Ford engines equipped with distributor ignition. (b) The connector

must be opened (disconnected) to check and/or adjust the

ignition timing. On DIS/EDIS systems, the connector is called

SPOUT/SAW (spark output/spark angle word).

Two Marks Are the Key to Success

When a distributor is removed from an engine, al-

ways mark where the rotor is pointing to ensure that

the distributor is reinstalled in the correct position.

Because of the helical cut on the distributor drive

gear, the rotor rotates as the distributor is being

removed from the engine. To help reinstall a distribu-

tor without any problems, simply make another mark

where the rotor is pointing just as the distributor

is lifted out of the engine. Then to reinstall, simply

line up the rotor to the second mark and lower the

distributor into the engine. The rotor should then line

up with the original mark as a double check.

TECH TIP

IGNITION SYSTEM

SYMPTOM GUIDE

Problem Possible Causes and/or Solutions

No spark out

of the coil



Open in the ignition switch circuit or theft

deterrent system fault



Defective ignition control module



Defective triggering device (magnetic

sensor, Hall-effect or optical sensor)

Weak spark

out of the coil



High-resistance coil wire or spark plug wire



Poor ground between the distributor or ig-

nition control module and the engine block

Engine misfire



Defective (open) spark plug wire



Worn or fouled spark plugs



Defective ignition control module (ICM)

Use a Water Spray Bottle to Check

the Secondary Ignition Circuit

To check for breaks in the insulation in the secondary

circuit perform the following steps:

STEP 1 Start the engine and allow to reach normal

operating temperature.

STEP 2 Using a water spray bottle set to mist,

spray the secondary ignition components

and listen for any change in operation.

STEP 3 If the engine operation is affected at all

there is a break in the secondary ignition

circuit insulation. Continue spraying to

pinpoint the exact location.

TECH TIP

IGNITION SYSTEM OPERATION AND DIAGNOSIS 377

5. A coil-on-plug ignition system uses an ignition coil for each

spark plug.

6. A thorough visual inspection should be performed on all

ignition components when diagnosing an engine perfor-

mance problem.

7. Platinum spark plugs should not be regapped after use in

an engine.

1. All inductive ignition systems supply battery voltage to the

positive side of the ignition coil and pulse the negative side of

the coil on and off to ground to create a high-voltage spark.

2. If an ignition system uses a distributor, it is a distributor

ignition system.

3. If an ignition system does not use a distributor, it is an

electronic ignition system.

4. A waste-spark ignition system fires two spark plugs at the

same time.

SUMMARY

5. Why should a spark tester be used to check for spark

rather than a standard spark plug?

6. How do you test a pickup coil for resistance and AC volt-

age output?

7. What harm can occur if the engine is cranked or run with

an open (defective) spark plug wire?

1. How can 12 volts from a battery be changed to 40,000 volts

for ignition?

2. How does a magnetic sensor work?

3. How does a Hall-effect sensor work?

4. How does a waste-spark ignition system work?

REVIEW QUESTIONS

7. The pulse generator ________ .

a. Fires the spark plug directly

b. Signals the ignition control module (ICM)

c. Signals the computer that fires the spark plug directly

d. Is used as a tachometer reference signal by the com-

puter and has no other function

8. Two technicians are discussing coil-on-plug ignition sys-

tems. Technician A says that they can be called coil-near-

plug or coil-by-plug ignition systems. Technician B says

that some can use ion sensing. Which technician is correct?

a. Technician A only

b. Technician B only

c. Both Technicians A and B

d. Neither Technician A nor B

9. A waste-spark-type ignition system fires ________ .

a. Two spark plugs at the same time

b. One spark plug with reverse polarity

c. One spark plug with straight polarity

d. All of the above

10. Technician A says that a defective crankshaft position

sensor can cause a no-spark condition. Technician B says

that a faulty ignition control module can cause a no-spark

condition. Which technician is correct?

a. Technician A only

b. Technician B only

c. Both Technicians A and B

d. Neither Technician A nor B

1. The primary (low-voltage) ignition system must be work-

ing correctly before any spark occurs from a coil. Which

component is not in the primary ignition circuit?

a. Spark plug wiring

Ignition module (igniter)

c. Pickup coil (pulse generator)

d. Ignition switch

2. The ignition module has direct control over the firing of the

coil(s) of an ignition system. Which component(s) triggers

(controls) the module?

a. Pickup coil c. Crankshaft sensor

b. Computer d. All of the above

3. Distributor ignition systems can be triggered by a ________ .

a. Hall-effect sensor c. Spark sensor

b. Magnetic sensor d. Either a or b

4. Ignition coil primary resistance is usually ________ ohms.

a. 6,000 to 30,000 c. Less than 1 to 3

b. 150 to 1,500 d. Zero

5. Coil polarity is determined by the ________ .

a. Direction of rotation of the coil windings

b. Turn ratio

c. Direction of laminations

d. Saturation direction

6. A compression-sensing ignition system uses a ________

type of ignition.

a. Distributor c.

Waste-spark

b. Coil-on-plug d. All of the above

CHAPTER QUIZ

378 CHAPTER 30

chapter

SCAN TOOLS AND ENGINE

PERFORMANCE DIAGNOSIS

OBJECTIVES: After studying Chapter 30, the reader should be able to: • Prepare for the ASE computerized engine

controls diagnosis (A8) certification test content area “E.” • List the steps of the diagnostic process. • Describe the simple

preliminary tests that should be performed at the start of the diagnostic process. • List six items to check as part of a thorough

visual inspection. • Explain the troubleshooting procedures to follow if a diagnostic trouble code has been set. • Explain the

troubleshooting procedures to follow if no diagnostic trouble code has been set. • Discuss the type of scan tools that are used

to assess vehicle components. • Describe the methods that can be used to reprogram (reflash) a vehicle computer.

KEY TERMS: Data link connector (DLC) 383 • Drive cycle 395 • Flash code retrieval 386 • Key-on—engine off test

(KOEO) 387 • Key-on—engine running test (KOER) 387 • Paper test 381 • Pending code 382 • Self-test automatic

readout (STAR) 387 • Smoke machine 381 • Technical service bulletin (TSB) 382 • Trip 391

CUSTOMER

SATISFACTION

FIGURE 30–1 A funnel is one way to visualize the diagnostic

process. The purpose is to narrow the possible causes of a

concern until the root cause is determined and corrected.

THE EIGHT-STEP

DIAGNOSTIC PROCEDURE

It is important that all automotive service technicians know how

to diagnose and troubleshoot engine computer systems. The di-

agnostic process is a strategy that eliminates known-good com-

ponents or systems in order to find the root cause of automotive

engine performance problems. All vehicle manufacturers recom-

mend a diagnostic procedure, and the plan suggested in this

chapter combines most of the features of these plans plus addi-

tional steps developed over years of real-world problem solving.

Many different things can cause an engine performance

problem or concern. The service technician has to narrow the

possibilities to find the cause of the problem and correct it.

Afunnel is a way of visualizing a diagnostic procedure.

쎲 SEE

FIGURE 30–1. At the wide top are the symptoms of the problem;

the funnel narrows as possible causes are eliminated until the

root cause is found and corrected at the bottom of the funnel.

All problem diagnosis deals with symptoms that could be

the result of many different causes. The wide range of possible

solutions must be narrowed to the most likely, and these must

eventually be further narrowed to the actual cause. The follow-

ing section describes eight steps the service technician can take

to narrow the possibilities to one cause.

STEP 1 VERIFY THE PROBLEM (CONCERN) Before a

minute is spent on diagnosis, be certain that a problem exists.

If the problem cannot be verified, it cannot be solved or tested

to verify that the repair was complete.

쎲 SEE FIGURE 30–2.

M30_HALD2920_03_SE_CH30.indd 378 15/12/10 6:08 PM

SCAN TOOLS AND ENGINE PERFORMANCE DIAGNOSIS 379

are performed. A sample form that customers could fill out with

details of the problem is shown in

쎲 FIGURE 30–3.

NOTE: Because drivers differ, it is sometimes the best

policy to take the customer on the test drive to verify

the concern.

STEP 2 PERFORM A THOROUGH VISUAL INSPECTION

AND BASIC TESTS The visual inspection is the most

important aspect of diagnosis! Most experts agree that between

10% and 30% of all engine performance problems can be found

simply by performing a thorough visual inspection. The inspec-

tion should include the following:

쏋

Check for obvious problems (basics, basics, basics). 

Fuel leaks

Vacuum hoses that are disconnected or split

Corroded connectors

Unusual noises, smoke, or smell

Check the air cleaner and air duct (squirrels and other

small animals can build nests or store dog food in

them)

쎲 SEE FIGURE 30–4.

쏋

Check everything that does and does not work. This

step involves turning things on and observing that every-

thing is working properly.

쏋

Look for evidence of previous repairs. Any time

work is performed on a vehicle, there is always a risk

that something will be disturbed, knocked off, or left

disconnected.

쏋

Check oil level and condition. Another area for visual

inspection is oil level and condition.

Oil level. Oil should be to the proper level.

The driver of the vehicle knows much about the vehicle

and how it is driven. Before diagnosis, always ask the following

questions:

쏋

Is the malfunction indicator light (check engine) on?

쏋

What was the temperature outside?

쏋

Was the engine warm or cold?

쏋

Was the problem during starting, acceleration, cruise,

or some other condition?

쏋

How far had the vehicle been driven?

쏋

Were any dash warning lights on? If so, which one(s)?

쏋

Has there been any service or repair work performed on

the vehicle lately?

NOTE: This last question is very important. Many engine

performance faults are often the result of something

being knocked loose or a hose falling off during repair

work. Knowing that the vehicle was just serviced before

the problem began may be an indicator as to where to

look for the solution to a problem.

After the nature and scope of the problem are determined,

the complaint should be verified before further diagnostic tests

CUSTOMER

SATISFACTION

–

CUSTOMER CONCERN

(VEHICLE PROBLEM)

–

FIGURE 30–2 Step #1 is to verify the customer concern or

problem. If the problem cannot be verified, then the repair

cannot be verified.

“Original Equipment” Is Not a Four-Letter Word

To many service technicians, an original-equipment

part is considered to be only marginal, and to get the

really “good stuff” an aftermarket (renewal market) part

has to be purchased. However, many problems can

be traced to the use of an aftermarket part that has

failed early in its service life. Technicians who work

at dealerships usually begin their diagnosis with an

aftermarket part identified during a visual inspection. It

has been their experience that simply replacing the af-

termarket part with the factory original-equipment (OE)

part often solves the problem.

Original equipment parts are required to pass

quality and durability standards and tests at a level

not required of aftermarket parts. The technician

should be aware that the presence of a new part

does not necessarily mean that the part is good.

TECH TIP

M30_HALD2920_03_SE_CH30.indd 379 15/12/10 6:08 PM

380

FIGURE 30–3 A form that the customer should fill out if there is a driveablilty concern to help the service technician more

quickly find the root cause.

M30_HALD2920_03_SE_CH30.indd 380 15/12/10 6:08 PM