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•i B ^ M B ^ B i B ' B ^ M ^ H

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How To Diagnose ai Repair Automotiv Electrical Systei

T o Leslie, w h o s e love a n d advice is a gift-

First published in 2005 by Motorbooks, an imprint of MBI Publishing Company, Galtier Plaza, Suite 200. 380 Jackson Street, St. Paul. M N 55101-3885 USA © Tracy Martin, 2005 All righrs reserved. With the exception of quoting brief passages for the purposes of review, no part of this publication may be reproduced without prior written permission from the Publisher. T h e information in this book is true and complete to the best of our knowledge. All recommendations arc made without any guarantee on the p a n of the author or Publisher, who also disclaim any liability incurred in connection with the use of this data or specific details. This publication has been prepared solely by M B I Publishing C o m p a n y and is not approved or licensed by any other entity. W c recognize that some words, model names, and designations mentioned herein are the property of the trademark holder. We use them for identification purposes only. This is not an official publication. Motorbooks titles are also available at discounts in bulk quantity for industrial or sales-promotional use. For derails write to Special Sales Manager at MBI Publishing Company, Galtier Plaza, Suite 200, 3 8 0 Jackson Street, St. Paul, M N 55101-3885 USA.

O n the front coven Main: Sometimes a lab scope is the only way to determine if an electrical component is doing its job. T h e waveform for one of the cighttfuel injectors on this Ford F150 looks good. Small: These components may appear different, but they're all just load dcviccs with resistance to electron flow. O n the back cover: A relay has been added to a driving light circuit. T h e relay now controls the high amperage load that the driving ligfits need to operate. For more on this, see Chapter 8.

ISBN-10: 0-7603- 2099-3 Editors: Jennifer Johnson and IVicr BodenMeincr Designer: Chris Faycrs Printed in China

CONTENTS Pr«tM«

J

SECTION I: P.HAPTFR 1

THEORY Ohm1. Law -Three Things* About 12-Volt DC Circuits •Three Things* About 12-Volt DC Circuits Resistance/Amps Relationship DC and AC Circuits Oh No. Math? Rules of Operation for Three Types of Circuits

CHAPTER 2:

Voltage Drop Testing nnn't I an Ohmmctpr How a Voltmeter Measures Voltage Testing Circuits Dynamically Voltage Drop How Mnrh k Tnn Mnr-h? Locating the Bad Spot Test. Don't Guess

1P 11 14 16 18 19 20

..

28 P7 28 30 32 . 33 35 36

SECTION II: TOOLS

CHAPTER 3: Electronic Testing Toolt

Test Ughts Multimeters Fluke Multimeter Measuring Amperage Logic Probes Noid Ughts Rhnrt Finder* Jumper Wires and Accessories Coil Testers Spark Tester Ignition Timing Lights Battery Testers Lab Scopes Soldering Tools

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38 40 42 45 46 46 47 49 50 51 53 53 54 55

S E C T I O N III; E L E C T R I C A L S Y S T E M S CHAPTER 4:

CHAPTER 5:

Storage Battery Chemical Reactions Discharging Electrolyte Solution Charging Battery Ratings Type ot Batteries Battery T e s t i n g - S t a t e of Charge

58 59 60 61 62 63 . . . .63 • • 64

Dynamic Battery Testing Hand-held Battery Testers

65 67

C h a r g i n g a n d S t a r t i n g Sy»temm n r : n«npratnr amperage is present then the orcut resistance is low

How

of

electrons,

causing

low

performance

or

n o n o p c r a t i o n of load devices.

resistance to electron flow becomes too low. T h e fuse heats u p w h e n amperage increases; at some point, amperage gets

T h e r e is a direct relationship between circuit amperage

high e n o u g h to melt t h e fuse in half, causing an incomplete

a n d circuit resistance. I t s critical to u n d e r s t a n d this simple

circuit. Fuses provide a margin of safety in circuits sincc a

cause-and-eflect

b u r n e d wire could cause an electrical fire. A n d a melted fuse

relationship because k n o w i n g h o w

to

apply this knowledge is key toward providing solutions t o m a n y a u t o m o t i v e electrical problems.

It's i m p o r t a n t t o r e m e m b e r the ins-ene

Both a slow t u r n i n g starrer and a d i m headlight arc the result of an

Ls easier to replace than b u r n e d wires.

insufficient n u m b e r of electrons

passing

between

resistance

relationship

and amperage. W h e n resistance in a

circuit is decreased, amperage always increases propor-

t h r o u g h the circuit back to the battery ( f o r m i n g a complete

tionally. Conversely, if a circuit has high

circuit). Somewhere along the circuit, high resistance has

available amperage is decreased.

resistance,

the

blocked the flow of current. T h u s , an increase in resistance DC AND AC

causes a decrease in amperage.

In a direct current ( D C ) circuit, the floss- of amps always runs

circuit is t o o low; a decrease in resistance causes an increase

in only o n e direction. For ease of explanation (and in confor-

in amperage. For example, if a power source wire comes

mance with automotisr publications), all diagrams used in this

i n t o contact w i t h a g r o u n d return (because of a loose

18

CIRCUITS

However, the opposite occurs whenever resistance in a

book depict dectriciry (electrons) lloss-ing through D C circuits

c o n n e c t i o n , frayed wire, o r another reason), t h u s bypassing

in one direction o n l y — f r o m a point of higher (positis-c)

the intended load dcvicc, the low resistance present in the

voltage to a lossrr (negative) voltage. EJectron floss- from

g r o u n d return allows high amperage t o flow through t h e

positive to negative is called conventional electron theory. (In

circuit. If the wires are t o o small t o carry the increased

reality, electron mos-ement at the subatomic lesxl travels only

amperage,

can

from negative to positisr in a D C circuit. See Chapter 4 for

possibly cause a Are. Fuses are used to protect circuits when

the explanation why.) However, since >1x1 can't sec the

they could overheat

and

melt, which

CAiin/E

\F\~W W

/

VOLTS • A M P S TIMES O H M S O H M S - V O L T S D I V I D E D BY A M P S A M P S - V O L T S D I V I D E D BY O H M S WATTS - AMPS TIMES VOLTS A M P S - W A T T S D I V I D E D BY VOLTS

Fig 1-6. These ar the Das* formulas needed to ffare out the 'numbers'in any 12-vott DC drcuK. To sobe tor any one unknown value. you onty need to few two of the three values—volts. amps, or ohms. The unknown variable can be determined by the simple mathematical equations above.

electrons while working o n a circuit, the direction in which

Furthermore, wiring configurations and c o m p o n e n t s for A C

the)- travel is irrelevant. T h e important thing to remember for

current arc generally not compatible with D C circuits.

practical purposes is that in D C circuits electricity always flows in only one direction. For purposes of illustration, the "hands-

OH NO, MATH?

on" subject matter of this book uses the conventional view,

Books o n electronics are always packed full of mathematical

based o n the simple assumption (even if not correct) that

formulas. If you get that glazed, far-away look w h e n faced

clcctrons in a 1X2 circuit always flow from positive to negative.

with cryptic equations like E • I / R , don't worry, this b o o k

By contrast, alternate current (AC) circuits (the type

keeps it simple.

typically used in American homes) reverse the direction of voltage 6 0 times per second. These alternating cycles of

W h e n diagnosing an electrical problem o n a car or truck, understanding

the

dynamic

relationship

between

forward and backward electron flow are called h e r n (Hz).

resistance,

T h i s voltage reversal, which also reverses current flow, gives

i m p o r t a n t t h a n any m a t h skills you m a y (or may not!) have.

this type of electrical power its n a m e — a l t e r n a t i n g current.

However, s o m e basic calculations will c o m e in h a n d y if you

amperage,

and

voltage

is

critically

more

A C circuits operate o n higher voltages t h a n D C circuits—

i n t e n d to a d d electrical accessories to your car. For example,

cither 120, 2 4 0 , or 4 4 0 volts for an A C circuit versus only

d o you have any idea h o w big the wires need to b e t o power

12 or 2 4 volts for a D C circuit.

u p that 2.000-watt stereo you bought? Should you install a

Be aware that s o m e clcctrical c o m p o n e n t s in a u t o m o b i l e s

larger alternator to a c c o m m o d a t e the stereo's power so you

produce only A C voltage, like the alternator a n d s o m e

get the sound you want? D o you k n o w the size of the fuse

c o m p u t e r sensors. However, w h e n an alternator produces

needed to protect the circuit f r o m meltdown?

A C voltage, diodes (which are electrical one-way valves that

T h e formulas listed in Figure 1 - 6 are designed to provide

allow current to pass in only o n e direction) w i t h i n the alter-

the

nator convert it to D C voltage before it reaches the battery.

amperage, and watts (power) in any circuit. In general,

N o electrical systems used in vehicles operate on A C voltage.

these should cover most c o m m o n circuitry design needs.

basic

math

neccssary t o

find voltage,

resistance,

[


ott are preset*

on the red we between the battery and bght but) (toed dewcet The hght butt uses up an arx)atie roOage Thus, the ground return wvv reads 0 votes ai the way back to the negattve battery term/nal

SOURCE 12 VOLTS

To determine the a m o u n t of any u n k n o w n voltage,

I t s i m p o r t a n t to remember this rule. By keeping it in

amperage, or resistance present within a particular circuit, the

m i n d , you'll be able t o d e t e r m i n e what t h e voltage should

values of two of die dircc potentials must be k n o w n — t h e

be at any point in a scries circuit. It a voltmeter gives an

third u n k n o w n value can be determined based on the values

unexpected result, you'll k n o w where t o look for the

of the other two. Performing a few simple mathematical

problem. Here's why:

c o m p u t a t i o n s allows simple calculation of electrical loads.

Figure 1 - 7 shows a circuit's p o w e r source as the positive

To find the voltage used in a circuit, just multiply existing

battery terminal as well as the wire i o n n c c t i n g it to the light

amps by ohms. Similarly, o h m s c m be calculated by dividing

bulb, which is the load device. A full 12 volts f r o m the

amps into voltage, likewise, amps can be determined by

power source are present at every point along the wire

dividing o h m s into voltage. If an acccssory you intend to install

between the battery and load device (measured using a

is rated in watts and you want to find out how many amps will

voltmeter). W h e n 12 volts reach the light bulb, it uses u p

be used in the circuit, just divide watts by volts. Conversely, if

all the voltage in the circuit. Since the greedy light b u l b uses

you want to find watts, multiply amps by volts.

all available voltage by t u r n i n g o n , n o n e is present o n the g r o u n d return wire o r at the negative battery terminal. (Not

RULES OF OPERATION FOR

quite true! T h e g r o u n d return wire also has a small a m o u n t

THREE TYPES OF CIRCUITS

of resistance to current flow, which causes some voltage to

T h r e e types of electrical circuits arc used in cars a n d trucks:

be present). C o n s e q u c n d y . the g r o u n d wire will measure

series, parallel, and series/parallel. Series a n d parallel circuits

d o s e t o 0 volts. C h a p t e r 2 o n Voltage I ) r o p T e s t i n g provides

are by far the most c o m m o n and can be f o u n d o n b o t h new

in-depth explanations of what t o expect from voltage

a n d older vehicles. Each type of circuit follows a set of

readings o n g r o u n d return wires. l or now, consider the

operational rules that govern h o w the circuit works. S o m e

g r o u n d wire essentially at 0 volts.

rules apply to m o r e tlian o n e type of circuit; others apply

T h e second rule of series circuits is: W h e n m o r e than

t o o n l y o n e type. K n o w i n g these rules and u n d e r s t a n d i n g

o n e load device is present in a scries circuit, the individual

how each circuit operates gives you the advantage you need

resistance of each load device divides the available voltage,

to diagnose most electrical problems.

t h u s a d d i n g t o the total resistance of the entire circuit. T h i n k of load dcvices in a series circuit as a strand of

Series Circuits

Christmas tree lights along a wire connected in series. Because

Naturally, there arc "three rules" regarding h o w a series

each bulb has resistance to current flow, each adds to the total

circuit operates. The first rule of scries circuits is: All available voltage in a series circuit will be used u p by the load device.

20

resistance of the entire circuit. This cumulative increase in the overall

circuit

resistance

correspondingly

decreases

the

amperage available for all the bulbs, thus keeping the strand

• • • • • • • • / of Christmas tree lights at a nice fire-safe, low-level wattage.

true; the load device uses u p all available voltage since all

In addition, each of the bulbs must share the available voltage

the individual light bulbs c o m b i n e d cumulatively use u p all

becausc all need some voltage to light up.

the available voltage in the circuit (equis-alent t o a single

Voltage in a series circuit is not a constant. It is divided

c o m b i n e d load device). T h u s , the g r o u n d return wire at t h e

between all tlx: load devices in the circuit, based upon the

last load device will measure d o s e to 0 volts. Figure 1 - 8 also

individual resistance of cadi specific load device. Its important

introduces the g r o u n d s y m b o l — t h r e e horizontal lines at

to remember that each load device in a scries circuit requires both

the end of the g r o u n d return wire. Anywhere this symbol

a posscr source and a ground return to operate. Because the load

is placed indicates the wire is r e t u r n i n g t o the negative

devices are linked together, the power source for one load device

battery terminal a n d / o r w h e n a g r o u n d strap, body, or

simultaneously acts as the ground return for another.

vehicle frame is used as a g r o u n d .

l or example, consider three light bulbs connected in a series circuit as in Figure 1-8. T h e first bulb (bulb 1) is

T h e third rule of series circuits is: amperage is the same at all points t h r o u g h o u t a series circuit.

I O g (£

powered by the originating power source—a 12-volt batter)-.

T h i s rule is t r u e for b o t h negative a n d positive sides of

£

T h e ground return for bulb 1 becomes the power source for

a d r c u i t . Figure 1-9 (on page 22) shows three ammeters

^

the second bulb (bulb 2). Bulb 1 uses 4 s-olts of posver from

measuring current in a series circuit a n d h o w t h e amperage

the 12-volt posver source (to light up) and then passes the

remains constant o n b o t h the power a n d g r o u n d return

remaining 8 volts to its ground return. Similarly, bulb 2 uses

sides of the circuit. Rule three illustrates t h e simple concept

u p 4 volts of as-ailablc voltage from the ground return of bulb

(but u n w a n t e d result!) that a bad wire or p o o r connection

I (bulb 2 uses the same voltage as bulb 1 to operate). T h e

(unsvantcd resistance) will affect d r c u i t amperage n o matter

remaining 4 volts of power pass into its ground return. Bulb

w h i d i side of the d r c u i t it's located o n .

3 takes the last 4 volts and uses u p all the voltage left in the entire circuit; consequently, its ground return has 0 volts.

Parallel

Circuits

Figure 1 -8 illustrates the division of voltage along a scries

Nearly all electrical circuits designed for cars or trucks are

circuit. It also proves the first rule of scries circuits still holds

parallel circuits. Fortunately, the rules for parallel circuits

Fig 1-8. Each 12-»ct1 but) (load Oerice) has a cfren. identical, tnayxXiaf resstance, resMng fn eouzl stunng offoeoverall avatiaiJe rottage The difference in votoje

the pchwr source and ground return for each txit) is 4 mfts. Conseoverty. each butb has enfy 4 kji» ofeiectrkaf pressure wiffj wftcft to operate

Smce att the MDs are designed to operate on 12 Wfs and not 4 rotts.frusshortfall n voltage tcr each but) causes alt ct ffvm to be dim

21

[

1 FN WW

/

SERIES A M P METERS

Fig 1 -9. Amperage wtibea* same cn both the power an) grow! sties c/ a crcut M three ammeters indicate the same amount of amperage (current' is flowing throughout Ore circuit

are basically the same as for series circuits, b u t with a couple

t o be (because total resistance of the entire circuit decreases

of notable exceptions.

as overall amperage increases, as in Figure 1-5).

T h e first exception is: voltage will be equal (the same)

T h e second exception is: each additional load device in

everywhere on the positive side of the circuit a n d will not

a parallel circuit lowers the total overall resistance o f the

be divided between load devices, like in a series circuit. T h i s

circuit a n d increases amperage.

is because each load device has its own wire, or conductor,

Figure 1-11 (on page 24) illustrates h o w the addition of

c o n n c c t i n g it to the power source. T h e same is also true on

more load devices to a parallel circuit causes the resistance

the g r o u n d return side; each load device has its own g r o u n d

of the entire circuit t o decrease and the amperage to increase

return. As a result, the g r o u n d return side of each load

(a teeter-totter effect)—unlike what occurs in a series

device registers 0 volts because each individual load device

circuit where the resistance of each load device adds to die

uses u p all original source voltage.

total resistance of the circuit.

Figure 1 - 1 0 displays 0 volts present on the g r o u n d return

To u n d e r s t a n d this concept better, consider the following

side of each individual bulb (load device) because each bulb

analog)'. Imagine there are 2 0 people in a room svith only o n e

uses u p all of t h e original power source voltage. T h e g r o u n d

exit door, a n d everyone has to exit t h r o u g h the door, thereby

return side of each b u l b operates just like the ground return

creating lots of resistance. I h e people represent amperage, the

side at the end of a scries circuit. However, with a parallel

room is t h e c i r c u i t , a n d their effort to get o u t is the resistance.

circuit, it is helpful to t h i n k of each load device as a simple

Because there is only o n e d o o r from which to leave, people

scries circuit itself—with a separate power source, load

slowly get o u t because of the effect of their c o m b i n e d

device,

22

and

ground

return.

Consequently,

as

more

resistance. N o w assume the same 2 0 people ate in a r o o m svith

load devices arc added to a parallel circuit, the greater the

2 0 doors. Everyone is able to exit the r o o m quickly because

amperage f r o m the power source t o the load devices needs

each leaves through a separate door. Because there are

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m o r e doors, there is less resistance in the flow of people. T h e

( 3 bulbs x 6 a m p s - 18 amps) must pass t h r o u g h t h e 20-

extra doors in the r o o m represent additional load d e s i c t t in a

a m p fuse. This isn't a p r o b l e m because rhe fuse w o n t melt

parallel circuit. Resistance to electron flow is reduced because

unless amperage exceeds 2 0 a m p s .

a parallel circuit has m o r e d o o r s (load devices) f r o m which the

However, at the end of the circuit is an clcctric m o t o r

electrons can exit. As stated before, w h e n resistance decreases

(another load device); it requires 12 a m p s to operate. As

in a circuit, amperage increases; so, a d d i n g m o r e load dcviccs

long as the m o t o r switch is o p e n , the circuit uses only 18

(doors) losverstotal resistance and increasescircuit amperage.

a m p s to light the bulbs and the fuse is adequate for this

Figure 1-11 (on page 24) illustrates how each individual

application. But if the m o t o r switch is closed (the m o t o r

circuit w i t h i n a parallel circuit operates like a series circuit.

n o w connects

Each has a power source, load device, and g r o u n d return.

requirement for the entire circuit increases t o 3 0 a m p s (18

to

the

parallel circuit),

the

amperage

T h e third exception is: a parallel circuit requires all the

a m p s from the bulbs • 12 a m p s f r o m the m o t o r - 3 0 amps).

power for t h e entire circuit t o c o m e f r o m the same power

T h i s a m o u n t exceeds the rating of the 2 0 - a m p fuse, so the

source (the battery). T h i s means the total amperage used by

fuse overheats a n d melts (in order t o protect the circuit),

all the load dcviccs must pass through the 2 0 - a m p fuse.

thereby c u t t i n g off power t o the entire circuit. For this

Since each of the 12-volt bulbs in the individual circuits

circuit t o work, the 2 0 - a m p fuse has to b e replaced with a

uses 6 amps, the total c o m b i n e d amperage for all the bulbs

fuse with a rating of more t h a n 3 0 amps.

I

Fig 1-10. Unito seres circuits. M»n the hgtrt bubs (kad devices)tinidetrie tou< to.1age between rwn. ttie Goto in a parallel droit are ndrnduaoy bnghter because each bulb operates on 12 vote and uses al of the penver source vottage

23

H I

-

from the batten- a n d the F wire is the field wire f r o m the voltage regulator. 'Fhe regulator has three wires, labeled F, 2. and 3. 'Fhe F terminal is the field control wire for the alternator: the 2 wire is key's on power; and the 3 wire goes t o the battery (see Figure 5-11 o n page 85). If this charging system isn't charging, the first step in testing is to check the wires at the voltage regulator. To d o this, remove the regulator connector and turn the ignition key t o O N . Terminals 2 and 3 (in Figure 5-11) should light u p a g r o u n d e d test light. Using an o h m m e t e r . test the F terminal for continuity to g r o u n d . If this wire is o p e n , a wire o n the field coil inside the alternator is o p e n . If all wires at the voltage regulator connector don't have proper electrical values, the charging system won't work. C o n s u l t a wiring diagram to d e t e r m i n e the originating posver source for each wire. If all the regulator wires are okay, a full field test of the alternator is next. To full field test this alternator, run the engine at 2 , 0 0 0 r p m and connect o n e e n d of a j u m p e r wire t o the big wire

This Deko Remy alternator features a test hole .it the back of the alternator

at the back o l the alternator. Touch the other end to the

Just stick a pocket screwdriver or Aten wrench nto this Me ami the alternator

field terminal o n the back of the alternator. T h e alternator

wHtuBMd Coulesy ot CAROUEST Auto Parts

Hfl 5-12. The BATT and F2 wires depicted here should haw lattery voltage Ft comes from the charge indicator Fight AHot these wres must have correct electrical values before an attenator wif won The back ot the alternators case has a smai hole labeled *test hole.'A smalt screwdriver inserted into this hole w/r MBdd the alternator.

86

uu-

*

u

• n

-

n

• > • >

n a w

If all the wires of the alternator hase corrcct clcctrical values, a full field test is the next step. Plug the connector back into the alternator and start u p the engine. Hold the engine at 2.000 rpm and insert a small scrcssdrivcr or Allen wrench into the regulator grounding hole (test hole), located at the back of the alternator. Doing this will full field the alternator, causing it (hopefully!) to produce full amperage (within 10 amps of its rated output capacity); if alternator output turns o u t less than expected, then it's time to shop for a new alternator. DELCO-REMY CS ALTERNATOR Delco-Remy C S alternators c o m e in t w o flavors—PLIS and PLFS. T h e y can be identified by reading the letters o n the plastic plug o n the back o f the alternator. PLIS alternators arc usually (but not always) f o u n d o n vehicles w i t h o u t a body control m o d u l e ( B C M ) , while vehicles svith PLFS alternators usually have a B C M . These two types of alternators arc not interchangeable, which can b e a p r o b l e m GM produces two CS alternators that can be identified by the tetters on the

when

purchasing a rebuilt alternator.

In addition

to

piastc ptys at the backs of the cases Each plug KYJ read either PUS or fUS d i c c k i n g the letters on the plug, m a k e sure you have the part n u m b e r t o m a t c h y o u r car or truck. DelcoThese alternators are not interchangeable, so make sore the correct one for corrcct the Remy C S alternators use a chargc indicator l a m p that must

vehxSe a nstated. Courtesy CAROUEST Auto Parts

be operational in order tor the charging system to f u n c t i o n . If the l a m p does n o t light u p w h e n the ignition key is should lull field and p r o d u c c m a x i m u m current. If alternator o u t p u t is less than expected, get a new alternator. G M DELCOTRON ALTERNATOR INTERNAL

WITH

REGULATOR

turned to O N . disconnect the plug f r o m the back of the alternator and ground the 1. terminal; the l a m p should n o w shine. If it doesn't, check for an o p e n i n g in the l a m p circuit or a b u r n e d o u t indicator bulb. T h e normal system s-oltagc produced by C S alternators is

G M v e h i d e s arc also c o m m o n l y equipped svith a Dclcotron

sonicsviiat losvcr than on other charging systems. A typical

alternator (also k n o w n as a Delco-Remy

I0-S1). T h i s

range of readings, taken at the battery's positive terminal with

charging system uses an internal voltage regulator a n d is

the key turned to O N and engine off is 12.3 to 12.5 volts.

easily identified by the presence of three wires connected to

W i t h the engine r u n n i n g at idle, the range should be between

the back of its case. T h e t w o smaller wires. B A T T and F2,

12.8 and 13.1 volts. W i t h all accessories turned on. the range

g o dirccdy t o the battery. T h e F l wire goes to the chargc

is between 12.8 and 13.3 volts. T h e internal voltage regulator

indicator light o n the dash (Sec Figure 5-12).

is designed to change the charging voltage slowly, so as to

T h e first step in testing this charging system is to verify that the charge indicator dash light works. If the indicator light doesn't come o n when the ignition key is in the O N position,

help the E C M keep engine-idling speed stable. A Delco-Remy C S alternator c a n n o t be full instead,

use

the

generic

alternator

test

fielded;

previously

the alternator won't chargc. If this is the case, the charging

m e n t i o n c d to check its current a n d voltage o u t p u t s . If the

light d r c u i t needs t o be repaired before further testing.

alternator cannot producc close t o rated amperage, the

To test terminals F1 a n d F2. u n p l u g die connector f r o m

wires at the alternator plug need to be checked for corrcct

the back of the alternator. Using a g r o u n d e d test light,

clcctrical values. T h e follosving are the electrical values for

touch each of the three wires, o n e at a time. T h e big svire

each of the wires for each type of C S alternator plug:

should light u p the test light brightly. O n e of t h e smaller wires (labeled F2 o n the diagram depicted in Figure 5-12)

• T h e P wire is an A C voltage signal used for tachometer

should also brightly light die test light. F l should light die

input (it is not needed for charging).

test light, too. b u t only dimly. If any of t h e wires don't light the test light as described, the alternator won't chargc a n d

• T h e L wire sends a signal to die B C M if die regulator is

the d r c u i t must be repaired before proceeding further.

working. Obviously this only occurs o n a B C M - c q u i p p c d

expert22

p,r\9\

http://rutracker.orq

87

vehicle; o n n o n - B C M - c q u i p p e d vehicles, the L wire lights the charge indicator l a m p and powers the regulator. • "I"hc P wire (again, only on a non-BCM-cquipped vehicle) carries tl»c power (with the key turned to O N ) used to turn on the voltage regulator. If the v e h i d e has a B C M , the F wire informs the B C M h o w hard the alternator is w o r k i n g T h e internal regulator switches die alternator's field coil o n and off at about 4 0 0 cycles per second—the a m o u n t of o n time determines charging o u t p u t . At high engine speeds and with losscurrent requirements, the on time may only be 10 pcrccnr. However, at idle or at low engine speeds with high loads, the on time can be as high as 90 percent. T h e signal can be read using a D V O M capable of measuring frequency.

• I"he I wire is used only on n o n - B C M - c q u i p p e d v e h i d e s and

receives

12 volts

from

the

ignition

switch

(or Shown is the ptast/c plug on a Delco-Remy at&mitjr This plug wS be marked

sometimes t h r o u g h a resistor).

PtfS ot PUS These alternators are not trttrchangeaste, so make sire you • Last b u t not least, the S wire senses battery voltage for

have the nght one tor your ratacte before installing.

b o t h types o f alternators.

dash

A TO ALT. 1

F £

1

>

ammeter

FIELD COIL a C O N T I N U I T Y T O G R O U N D (CHECK USINC O H M M E T E R ) BATTERY VOLTAGE W / I G N I T I O N KEY O N

A*

BATTERY VOLTAGE ALL THE TIME

1

N O T USED W I T H D A S H A M M E T E R

w

idiot TO ALT.

light

FIELD C O I L - C O N T I N U I T Y T O G R O U N D (CHECK U S I N G O H M M E T E R ) S T A T O R • 6 / 7 VOLTS - - F ' A N D "A** J U M P E D . ENGINE R U N N I N G BATTERY VOLTAGE ALL THE T I M E CHARGE INDICATOR L A M P • BATTERY VOLTAGE W / I G N I T I O N KEY O N

Ftg

Full tMog is accooipttsried in the san* nwmr & oolfi types ot Forcrs ctutgng systems to full tie*), jump termnM f trm^nA*. Theantmalor

shard poaxe amperage ntmtn to percent ot Its rated output capaotr88

-l-jafe^"

u

This Ford M/f alternator has two ptues The plug on the backed the alternator ittock colored, upper left) is tne rottage regulator. The brown p\jg on the side ct the afternator is tor highamperage output wires going emery to the battery Courtesy ol CAflOJCST Auto Parts

i o to

z 0

If all the wires at the plastic plug have correct voltage

die regulator conncctor must be repaired. (See Figure 5-13 to

readings a n d the C S alternator fails the generic alternator

identify terminals on cither regulator.) If the wires to the

test, the answer t o y o u r charging problem is a new alternator.

1 i

rcgularor hasr corrcct elcctrical salues, but the alternator docs not producc amperage within 10 percent of its rated output

FORD ALTERNATOR EXTERNAL Ford vehicles equipped

WITH

during a full fidd test, it's time for a new alternator

REGULATOR

with alternators controlled

by

FORD-MOTORCRAFT IAR

external voltage regulators use different pairs of alternators

Ford-Motorcraft

and

regulators. T h e s e

regulators

that

arc

not

interchangeable.

One

regulator/alternator pair is in vehicles with an a m m e t e r o n

IAR

alternators

alternators

can

ALTERNATORS use be

internal full

voltage

fielded

by

g r o u n d i n g the F terminal located o n the regulator at the

the dash: the other is in vehicles with a charger indicator

back of the alternator. If t h e alternator doesn't p r o d u c c full

light. Both regulators have four terminals, labeled F, S, A*,

current o u t p u t , check the conncctor(s) plugged i n t o the

and 1. and both alternators hase four wire connectors that

alternator. Ford alternators with o u t p u t s of 6 0 a m p s usually

plug into the regulators (see Figure 5-13).

have o n e three-wire conncctor: higher o u t p u t units may

To hill field either alternator, unplug the four-wire conncctor

have t w o three-wire connectors.

from the regulator, start die engine, and maintain rpm at 2,000.

To test an alternator e q u i p p e d with only o n e three-wire

Using a jumper ssire, conncct the regulator harness of terminals

connectcr, u n p l u g the c o n n c c t o r a n d t u r n the ignition key

F and A+ together. T h e alternator should full field and produce

t o O N . Using a voltmeter, check the terminals at the

maximum ourpur. If it doesn't, there may be a problem with the

conncctor as follows: terminal I (connected to the chargc

wires between the alternator and regulator connector, so the

light indicator), terminal S (connected directly to the

same test should be performed again, but this time try

battery), a n d

connecting the battery and F terminal together at the back of

switch—it receives key o n power, svhich it sends t o the

die alternator. If the alternator full fields now, the wires going to

regulator). All of these should read 12 volts.

terminal

A (connected

to

the

ignition

89

other should cither m a k e the test light dimly light up, or n o t at all; this wire (usually green) is ordinarily the g r o u n d used to full field the alternator. Start the engine a n d hold r p m at 2 , 0 0 0 . Using a j u m p e r wire, momentarily connect the field wire to g r o u n d t o full field the alternator. If the alternator o u t p u t has correct amperage, it's time for a new voltage regulator. If the o u t p u t isn't .it m a x i m u m , try a full field test again, b u t diis time p e r f o r m die test at t h e back of the alternator. If it full fields now. simply repair the broken field wire. If it still svon't full fidd, there's n o other o p t i o n — i t ' s definitely time for a new alternator. CHRYSLER'S

COMPUTER-CONTROLLED ALTERNATOR

Chrysler's computer-controlled alternators arc similar to those alternators using external volrage regulators

Look for t w o

small svires (usually green) at the iuck of the alternator. O n e Thra Ford tAft a/iernator uses an ntemal voltage regulator. -Ground here to of these wires comes from the ignition sw itch and should have test'is marked on the regulator To M Md the axemator the F terminal on the 12 volts when the key is turned t o O N . T h e odier comes from the power module and controls die ground of the alternator's

regdotor c£>s cottnxl the tattery Onctt/to the starter 3nd engage the starter pawn gear with tt\e engine flywheel. Courtesy of ttunQW Toyota

generator, a starter m o t o r uses field soils to create a magnetic field around an armature, which in this case is a series of wire loops connected at a c o m m u t a t o r . W h e n die starter m o t o r is operating, current from the battery energizes the field coils, causing them t o have a strong magnetic field. At the same time, batter)- current is applied to tlie c o m m u t a t o r brushes (that carry current from the battery t o the armature). The armature rotates because the opposing magnetic lines of forcc between the field coils and armanire repel each other, a n d since the armature lias multiple wire loops, it r o u t e s continuously. Starter motors may use as m a n y as four c o m m u t a t o r brushes and f r o m two to four field soils. T h e armature and fidd coils arc in series, a design which causes a very high torque output from the starter. With the fidd windings and annaturc in series, any iiu.rea.se in current produces Ths aftermarket starter prwdes 25 percent mere torque than the onprol starter an increase in field strength. As the load on the staner increases, it replaced The starter shaft is heat-treated art rotated n Bend* bearings tfofso docs the starters torque. Under a n o load condition, such .LS prevde reliability and long Irfe. Courtesy of SommrtfacingEquipment during staner bcnch testing or when a starters pinion gear doesn't engage the flywheel* the staner speed will continue to increase battery, die field circuit inside die generator is open and

until centrifugal force destroys the staner. It then nukes a b u d

needs to be repaired. This may involve finding a break in the

"bang," followed by a shower of sparks.

wire and replacing it with a new section of wire.

Certain s t a n e r m o t o r s use gear sets t o increase c r a n k i n g speed a n d torque. A planetary gear set (similar to those used

STARTER

MOTORS

A D C starter m o t o r operates m u c h like a D C generator—

92

in a u t o m a t i c transmissions) sends power between the starter m o t o r and o u t p u t shaft connected to the engine flywheel.

only in reverse. It uses current t o operate, instead of

Ncsvcr s t a n e r m o t o r s use p e r m a n e n t magnets instead of

p r o d u c i n g current w h e n it spins. However, just like a

field coils which increases c u n c n t going t o the a r m a t u r e .

Using an inductive amp probe. kk» Wis fhikeHJO. wit confirm wMher a starter's current draw e too Itgh or too low This test is taster and easier Um replacing a starter—otff to find out later that some other component was the real aJtpni Courtesy of Fluke Corporation

STARTER

SOLENOIDS

in trying t o figure o u t w h i c h part of a starter circuit is bad two,

if t h e battery doesn't have e n o u g h energy t o c r a n k it. even

f u n c t i o n s ; they c o n n e c t the battery directly t o t h e starter,

w h e n nothing's w r o n g . (See C h a p t e r 4 , Storage Battery,

and on s o m e starters, also engage the p i n i o n gear svith the

for testing a n d / o r c h a r g i n g procedures.) T h e only real

Starter

solenoids

perform

one.

and

sometimes

engine flysvhccl. Solenoids can be m o u n t e d directly o n t o

reason t o test a starter is w h e n it's c r a n k i n g an e n g i n e t o o

the starter ease o r used remotely. T h e y are really just

slowly t o start it or n o t c r a n k i n g at all. In certain f r o n t -

overgrown relays that use a small a m o u n t of current t o

svhccl-drivc cars, the starter m o t o r is difficult t o remove

energize a coil of wire t o p r o d u c c a magnetic field. T h e

(to say the least!). By contrast, p e r f o r m i n g basic starter

strength of the m a g n e t i c field pulls t h e s o l e n o i d s plunger

testing takes only a few m i n u t e s and is a m u c h m o r e

battery

productive use of t i m e t h a n s p e n d i n g six h o u r s c h a n g i n g

positive and t h e o t h e r to the starter. Positisx engagement

o u t a starter, o n l y t o find t h e p r o b l e m is really a bad

into

contact

svith

two

terminals—one

from

starters use a shift fork, o r a lever, that is c o n n c c t c d t o the

battery cable. In fact, rather t h a n testing a starter, it's

solenoid m o u n t e d directly o n t o the starter. W h e n

the

easier t o test everything else first. If the wires, cables,

starter receives battery voltage, the solenoid moves the

c o n n e c t i o n s . 3 n d solenoid arc g o o d , the starter is the only

lever, causing the starter to engage the engine's

t h i n g left t o rcplacc.

flywheel.

Starters using r e m o t e solenoids have moveable pole shoes that move a yoke w h e n the starter is energized. T h e yoke pushes the drive gear i n t o t h e flywheel in order t o crank t h e engine.

T h e test that provides the most information with the least a m o u n t of work is a starter current-draw test. To perform this test, conncct an inductive a m m e t e r to the positive battery cable, turn the headlights on. a n d read the ammeter. If it reads negative, the probe is conncctcd correal)-; if it reads positive,

STARTER

TESTING

turn the a m p probe 180 degrees and reconnect it. Don't

Before testing a starter m o t o r , t h e vehicle's battery m u s t

forget to turn off the headlights. Then get ready for the next

b e fully charged and load tested. T h e r e ' s simply n o p o i n t

step—disabling the ignition system.

93

The t*gh mXage coil wre has been grounded using a jumper wire This prevents the engtne trom starting up when testing a starter motor.

Disabling the Ignition

System

servicc manuals provide m o r e specitu n u m b e r s , b u t these

T h e next step is to prevent the ignition or fuel injection

work most of the time for testing purposes. Gcar-rcduction

system from starting the engine when the s t a n e r m o t o r is

a n d p e r m a n e n t magnet type starters yield slightly different

crankcd. O n older cars with only o n e ignition coil, find the

results; be sure t o check their scrvicc manuals for starter

wire going from the distributor cap to the coil, remove it

d r a w specifications.

from die distributor cap, a n d connect a jumper wire. C o n n e c t the other end of the j u m p e r to g r o u n d ; this will

Slow Turning Starter—High

Amperage

present the engine from staning because the spark from the

Although a slow-turning staner with high amperage is not

coil bypasses the spark plugs a n d goes dirccdy to ground. By

c o m m o n l y encountered, it docs occur occasionally, so follow

simply unplugging the ignition coil (without g r o u n d i n g it

the next procedure to diagnose this problem. Turn

first) and cranking the engine, the ignition module or other

ignition key to S T A R T position, then crank the engine osxr (do this even if the staner w o n t crank at all) and check the

distributors, to disable the ignition system, simply u n p l u g the

ammeter reading. If the a m p reading is excessively high

connector going to the ignition module or locate and remove

the engine is turning too slowly or not at all, there may be a

any fuse(s) that power(s) the c o m p u t e r or ignition system.

problem with the starter motor or engine. To eliminate the engine as the cause of a slow-turning staner. turn

Normal Starter Amperage

Draw

Before a b n o r m a l starter a m p d r a w can be recognized, you must first k n o w svhat normal looks like. All of the following specifications for s t a n e r draw assume an a m b i e n t t e m p e r ature above 6 0 degrees Fahrenheit a n d a conventional starter m o t o r c r a n k i n g an engine. A four-cylinder engine should d r a w between 50 a n d 125 a m p s ; a six-cylinder and a small V-8 require between 75 a n d 175 amps; and a large V-8 engine draws in the range of 100 to 2 7 5 a m p s . S o m e

94

the

p a n s can be wiped out. O n later model vehicles without

an

d

the

crankshaft by hand using a breaker Kir and socket. O n a fourcylinder engine, try grabbing the alternator/water

pump

drive-belt as a means of nirning it. Even with spark plugs installed, the engine should rotate with relatively little forcc. If it takes both feet and arms to move the engine minimally, a bad s t a n e r is the least of your problems. T h e engine could have a mechanical problem like liigh-viscosiiv oil in sveather colder than 2 0 degrees Fahrenheit or carbon build-up in the cylinders. Another possibility is that there is n o oil a n d the

total voltace drop

starter

0

1 a o

Fig 5-14. Ground side resistance n Otis starter cmxt Is okay because the voltage drop s omy 04 vo9. The po$>ttire side also has a voltage drop of 09 volt caused byfi>ghresistance as wit By moving the black lead along the positve sde ol the circuit, the pom! ol Itgb resistance can be located

crankshaft has welded itself o n t o the connecting rods o r

first, as it is the most likely place for problems to occur.

overheated,

problems.

C o n n c c t the red lead of a voltmeter to the positive battery

(Conversely, if the engine turns okay, get a new starter

causing

other

mechanical

terminal (not the battery cable). C o n n e c t t h e black lead to

because the flow of high amperage into the starter circuit

t h e starter terminal svhere t h e battery cablc attaches. C r a n k

indicates a shorted starter armature or field coil—not an

the engine over while ss-atching the voltmeter. If the voltage

engine problem.

d r o p is less than 0.5 volt, the positive side of the starter circuit doesn't have high resistance. D o the same test on the

Slow Turning Starter—Low

Amperage

g r o u n d side of the starter circuit. C o n n c c t the red lead to

If. o n the o t h e r h a n d , the a m m e t e r reading is low a n d t h e

the starter case and the black lead to the negative terminal

starter turns slowly or n o t at all. t h e starter circuit has high

on the battery, and then crank the engine. T h e voltage d r o p

resistance that is possibly caused by p o o r battery cablc

should not exceed 0.4 volt. If either the positive or negative

c o n n e c t i o n s or bad solenoid. H i g h resistance is, by far, t h e

side of the starter circuit cxcccds m a x i m u m voltage d r o p

most c o m m o n reason for losv starter circuit a m p e r a g e . It

(see chart under section Hosv M u c h Is T o o Much? in

can't possibly be a battery p r o b l e m since the battery's

C h a p t e r 2), the point of high resistance can be located by

already been tested a n d charged b e f o r e h a n d

(right?).

p e r f o r m i n g a voltage d r o p test across individual connec-

T h e r e f o r e , a voltage d r o p test is n o w an ideal test t o use

tions. T h i s can be accomplished by disconnecting the black

to locate t h e source of unsvanted, high resistance in t h e

lead and moving it back along the circuit toward the red

starter circuit.

lead. T h e r e should be n o m o r e than 0 . 2 volt lost across any

T h e positive side of the starter circuit should be tested

connection. C l e a n i n g a bad c o n n c c t i o n is fortunately all that's required to get the starter to spin faster in most cases.

95

CHAPTER 6 IGNITION SYSTEMS I

gnition-related problems, w h e t h e r real or perceived, are

method

t h e cause of m o r e needless replacement o f parts t h a n any

electronic ignition systems (EIS), since they sscre far more

o t h e r a u t o m o t i v e electrical system. Before rhe advent of f u d

before simply

throwing t h e m asvav and replacing t h e m . M o d e r n ignition systems are not as difficult to diagnose as you may think, as

c o m f o r t a b l e d o i n g this. T h e y often fixed ignition m a l f u n c -

there arc a great n u m b e r of similarities between conven-

ss-ith

simple

replacement

standard coil t&tx or an electron* ignition moduie and high-energy coil (nght) Figuring out what's good or bad with each ot them s not as hard as

96

m o r e cost-effective ro test c o m p o n e n t s

retor for engine stalling, missing, a n d n o starts, and since it

Both at these sets ot components

o

of

could be taken apart and visually inspected, they felt

plug points, condenser, and

o

introduction

Today, electronic engine m a n a g e m e n t systems control

produce an arc across a spark

e z

the

ignition systems o n all vehicles. Consequently, it's m u c h

of points,

condenser,

ignition coils, wires, and spark plugs. In early 1970, this

z

svith

injection, m a n y people often t h o u g h t that most carburetor

tions

i

changcd

problems could be fixed by looking inside the distributor. Mechanics and owners alike most often blamed the carbu-

(/) g

of repair

costly to replace.

you may think

tional points-type ignition systems and electronic ignition systems. A basic u n d e r s t a n d i n g of how primary

and

Fig 6-3. An ohmmeter »HI only let you H the windings are open or shorted. The coit may check out okay, but sta may not produce a spark Sometimes hitbng a col with a scrmvdnver or heating it with a hair dryer wit bmg out the tod section of win.

SECONDARY WINDING

CONVENTIONAL COIL

collapses. voltage is induced into the secondary windings. Electrons flosv f r o m the positive end of the secondary w i n d i n g s t o the first spark plug a n d across the air gap p r o d u c i n g a spark. After reaching the first spark plug, current passes t h r o u g h the cylinder h e a d — t h e equivalent o f a really big w i r e — t o the second spark plug's g r o u n d elcctrodc. where it j u m p s the air gap and produces a spark. Fach coil pair fires o n e spark plug in the n o r m a l direction and the other plug in reverse. After j u m p i n g the air gap of the second plug, t h e current rcrurns to the other side of the secondary w i n d i n g s — t h e g r o u n d side of that coil (see Figure 6-2). T o make sense of this type of circuir, think of the secondary windings on a D I S coil as having n o t h i n g to d o with the vehicle's battery ground. Each coil pair fires the spark plugs in two cylinders simultaneously. Both cylinders arc at "top dead center" in the crankshaft's rotation. O n e cylinder is on its compression stroke and the spark ignites the air/fuel mixture. T h e other companion cylinder is at the end of its exhaust stroke, so the second spark has n o effect because there is n o t h i n g to burn inside the combustion chamber. The difference between the IXScoi ftett) and a camenticnal coi s that the OS GENERIC COIL TESTING

coi s secondaryrnndmjsare not connected to the primary ctrcuit Thisdesgn

Both types of coils can b e chcckcd for o p e n s or shorts using

causes the spark produced by a DS cot to go to the other sde of the

an o h m m e t e r . To check resistance on a conventional coil.

secondary wvxfngs and not the battery ground.

99

Tins ignton con is being bench-tested The yellow wire is 12 volts and the nve coming out of the coJ tester goes to ground,rt'teirthe peaty end ot the cot tester is tipped on the negative coi terminal, a spark is produced

conncct o n e o h m m c t c r lead t o the negative side o f the coil

secondary windings, try t a p p i n g on the coil with a screw-

and the other to positive. Primary circuit resistance should

driver handle or heating it with a hair dryer. If the

read between 1.5 a n d 3 . 5 o h m s . Resistance in the secondary

o h m m e t e r s readings change, the toil svindings are b r o k e n .

circuit can be measured by c o n n e c t i n g o n e o h m m c t c r lead

You can also m a k e an inexpensive uniscrsal ignition coil

t o the negative coil terminal a n d t h e other to the high-

tester o u t of an old condenser and some j u m p e r wires.

voltage tower; it should be between 7 . 0 0 0 and

15.000

M a k e sure the condcnscr is good b y testing it o n a knosvn

o h m s . R e m e m b e r , the primary a n d secondary windings are

good coil. To use the tester, disconnect the negative side of

not connected in a D I S coil. Consequently. D I S p r i m a r y

the coil a n d conncct the condenser wire to the negative coil

circuit resistance should measure between 0.5 and 2.0

terminal. T h e n g r o u n d the condcnscr's m o u n t tab using a

o h m s , while secondary circuit resistance should be f r o m

j u m p e r wire. C o n n e c t a second j u m p e r wire to g r o u n d a n d

5 . 0 0 0 to 7 . 0 0 0 o h m s . A service manual will provide specific

t u r n the ignition key t o O N . N o w tap the g r o u n d e d j u m p e r

resistance values, b u t the n u m b e r s gis-cn here arc close

wire to the negative side of the coil; it should produce a

e n o u g h to d e t e r m i n e if there is a problem with the coils

spark between the high-voltage terminal a n d g r o u n d o n

windings. However, measuring ignition coil

a conventional coil, or between high-voltage terminals o n a

resistance

cannot conclusively d e t e r m i n e whether a coil is bad, since

D I S coil (see Figure 6 - 4 ) . If you don't get a spark, chcck for

a coil can check o u t okay with a n o h m m c t c r b u t still n o t

battery voltage at the coil a n d good connections o n all

p r o d u c c a spark w h e n electrically loaded (sec Figure 6 - 3 ) .

j u m p e r svircs. Be particularly careful when d o i n g this o n a

T h e r e arc a coupic of additional things you can d o when a t t e m p t i n g to discover if you're dealing with a bad coil. W i t h the o h m m c t c r conncctcd to the coil's primary or

100

D I S coil; the spark p r o d u c e d can really zap you if you get in the way. M o r e i n f o r m a t i o n regarding coil testers can b e f o u n d in C h a p t e r 3 o n electronic testing tools.

This luK-etfectsnitch (left) is fera Fortvetxte. The wtiitoplastic conmctor

)nsxSe this optcal dsirtxito/ rrere arB 360 rrtes on the outer nng of

(new cermets the switch to the Ignition module Coulesy ct CAROUEST

disk—one tor each crarMun degree The mnerrnjhas tour holes, one tor each

Auto Parts

CfMor. The larye tide a for cytiodor ntrrtxr c/f n fir cmne's fcrrn order

blade, and three-wire connector (the latter distinguishes it

to a lower voltage (sometimes 0 volts) and back. If a signal

f r o m an A C p i c k u p coil or other speed sensor o n a wiring

is not present, try the other wire that had voltage o n it, since

diagram). T h e three-wire connector has power, g r o u n d , and

you may have read the reference svire b\ mistake.

signal wires going to the c o m p u t e r or ignition module.

In addition

t o testing a hall-cffcct switch

meat

with a

A hall-clfcct switch is powered by a reference voltage sent

voltmeter, a logic probe can also be used. C o n n e c t the logic

by the computer. It is always equipped with a magnet

p r o b e to the vehicle's battery. l e a v e the hall-cffcct switch

situated opposite the switch; between t h e m is a series of

connected and back probe the signal wire. C r a n k the engine

rotating shutters (or blades)—one for each cylinder. As the

using the starter a n d watch the L E D o n the logic probe; it

blades rotate between the sensor and magnet, the magnet's

should indicate a pulse. If it doesn't, check t o make sure

magnetic field is interrupted and voltage d r o p s at the

there is b o t h power ("reference voltage"

sensor. T h e o u t p u t signal from the hall-effect switch is a

source t o the hall-cffcct switch, as well as for broken wires

square wave, or scries of o n - a n d - o f f pulses. T h e s e pulses arc

or loose connections.

and a g r o u n d

sent to t h e vehicle's c o m p u t e r or ignition m o d u l e , which use t h e m to calculate engine r p m a n d crankshaft position. To test a hall-effect switch, t u r n the ignition on a n d back

106

Optical

Sensors

An optical sensor is a n o t h e r f o r m of trigger for an ignition

p r o b e each of its three wires with a voltmeter. A process of

module. It typically consists of an L E D , a phototransistor.

elimination will help identity what each wire is used for.

a n d a rotating metal disk with holes in it. (Some optical

T h e voltmeter display should indicate that o n e wire is

conversion kits that arc used t o rcplacc a set of points have a

reference voltage, which should have between 2.5 and 12

plastic shutter instead o f a metal disk. > These sensors provide

volts d e p e n d i n g o n year, make, and model of the vehicle

trigger signals for ignition switching and generally can be

being tested. A n o t h e r wire is the g r o u n d wire and has n o

distinguished from other speed sensors on a w iring d i a g r a m

voltage; the third wire is a signal o u t p u t wire from the hall-

by the presence of four wires. 1'he signal o u t p u t from an

effect switch. T h e voltmeter will show cither reference

optical sensor's c o m p u t e r takes the f o r m o f a square wave

voltage or a value less than reference voltage, d e p e n d i n g

m a d e u p o f o n - a n d - o f f p u l s c s (similar t o a hall-effect switch).

u p o n w h e t h e r or not a shutter blade has stopped rotating

W h e n in use. a beam of light from the L E D is projected

between the hall-effect switch and the m a g n e t . T u r n the

through the holes in the disk o n t o the phototransistor. As the

engine over by hand a n d watch the signal wire. If the hall

disk rotates, the spaces between t h e holes interrupt the light

switch is working, voltage will switch f r o m reference voltage

beam. Each time the light beam is interrupted, a pulse is

WAVE FORMS

O VOLTS

A YA A A YJ Y Y Y

ac pick-up coil

hall effect switch

O VOLTS •

O VOLTS O VOLTS -

I]

EL

nnnnnnnnnnnnnnnn

optical distributor

-timeFig &-7. An AC pctujp col's wave form shows AC vOtagefransrtxwiogbetween negatrre and positive as the sensor is rotated Beth the haB-etfect switch and opbeat sensor produce a square ware The opocv sensor has two signals—cyMder xtentfication and engine rpm (tower wws form)

generated by the sensor's processor. S o m e optical sensors arc

points. Points reccivc engine rotational speed i n f o r m a t i o n

really two sensors in one: o n e measures crankshaft angle, the

by direct mcclianical m e a n s — t h e y o p e n a n d close, t u r n i n g

other measures camshaft position and identifies which

the ignition coil o n and off. An ignition m o d u l e p e r f o r m s

cylinder is the n u m b e r o n e cylinder in die engine's firing order.

the exact same f u n c t i o n , only it uses a trigger signal. O n c e

T o test an optical sensor, use a voltmeter to measure

a trigger signal (or wave f o r m ) is produced by t h e engine's

voltage on all the svircs going to the sensor. W i t h the

speed sensor, the ignition m o d u l e processes it and then fires

ignition key t u r n e d to O N . o n e ss'ire should read 12 volts

the coil. Later model vehicles use o n b o a r d c o m p u t e r s in

and the g r o u n d wire should read 0 volts. However, it's

conjunction

difficult to d e t e r m i n e if b o t h signal wires arc w o r k i n g using

switching. Either way, the basic operation of an ignition

only a voltmeter. A logic p r o b e is the better tool for

module is equis-alcnt to a set of points.

with

ignition

modules

to

control

coil

detecting the presence of pulses o n each signal svire. W i t h the logic probe connected to the battery, back p r o b e each

GENERIC IGNITION MODULE

TESTING

signal wire a n d crank the engine. T h e r e should be a pulse

W h e n electronic ignitions svere first introduced, many techni-

on each wire: if there is n o pulse, check for oil or dirt

cians had trouble diagnosing no-spark problems. Without any

blocking the holes on the metal plate. Also, m a k e sure the

moving pans to check, it was visually impossible to determine

sensor has b o t h posver a n d g r o u n d .

if primary coil switching was occurring, l-ortunatcly. today, even though you can't see a transistor operating, you can see

IGNITION

MODULES

the results of primary switching—just like on a set of points.

In its most simplistic f o r m , an electronic ignition m o d u l e

"I"hc first step in the proccss of determining if an ignition

is n o t h i n g m o r e than a m o d e r n replacement for a set o f

module is operational is a testing procedure originally used on

107

w , to/from ecm

BIG S P A R K

powerand ground

from crank sensor Fig 6-10. This module and coris are used on 28- art 3 G M

cars With ewry-Mig plugged W. tapping on terrmna/s A and C at toe thrre-wve ccmector should

produce a spark trom one oftoecois it toe module is good the m o d u l e and the coil pack has correct resistance, the

tl»c wires from the distributor t o the m o d u l e are not

m o d u l e is most likely bad. T h i s test can also be performed

connected, or (3) the distributor is n o t turning.

with the module/coil pack o u t of the vehicle. Just b e sure

If you don't get a spark, all the wires going t o the

to supply power and g r o u n d t o the two-wire connector at

m o d u l e must be checked with the engine cranking. W i t h

the m o d u l e , a n d t h e n perform the tap test as described, as

b o t h the two-wire a n d four-wire c o n n e c t o r s plugged i n t o

in Figure 6 - 1 0 .

the m o d u l e , back p r o b e each wire. T h e black wire should read 0 volts, the purple a n d orange wires should have about

Ford M o t o r

Company

0 . 5 volt AC, a n d the green wire should p r o d u c e a pulsing

T h e r e is a different tap test for 1975 to 1990 Ford Dura Spark

signal that can be checked with cither a logic p r o b e or h o t

ignition systems. T h e Dura Spark system is best identified by

test light. 'I'he two-wire c o n n e c t o r should have battery

wliat's insklc the distributor. I-ook for an A C pickup coil,

voltage in b o t h the R U N a n d S T A R T ignition positions.

mechanical advance (weights and springs), and a vacuum-

If t h e purple a n d orange wires don't have 0.5 volt A C w i t h

advance. Dura Spark modules are typically m o u n t e d inside

the e n g i n e cranking, the A C p i c k u p coil may be bad. T h e

the engine compartment, usually o n the fender ssell. T o test the module, disconnect the ignition coils highvoltage lead to the distributor and install a spark tester in its place. W i t h all wires connected to the module, back p r o b e the orange wire (module side of the wiring harness) with a test light. C r a n k the engine over and leave the ignition key

p i c k u p coils resistance should read between 4 0 0 a n d 1.300 o h m s . T h e ignition coil's resistance should also b e checked; primary resistance should be 0 . 8 t o secondary

resistance should

1.6 o h m s , while

read between 7 , 7 0 0

and

10.500 o h m s . Ford used a thick film ignition ( T F I ) from 1982 t o

in the R U N position—this initializes the module. (Don't

1 9 9 3 . T F I systems use a spark o u t p u t ( S P O U T ) connector.

use a remote starter to crank the engine or this tap test won't

T h i s is a removable connector that disconnects the ignition

work.) Next, tap the test light t o the positive or negative

module from the vehicle's computer. T h e first step in

battery terminals. If the m o d u l e is good, the ignition coil

diagnosing a T F I no-spark p r o b l e m is to u n p l u g

should produce a spark. If you get a spark, there arc three

S P O U T conncctor. T h e n crank the engine a n d check for a

possibilities: (1) the A C pickup coil is shorted or o p e n . (2)

spark. If you get a spark, check for a b u i n e d fusible link, a

the

111

GROUND PICK-UP COIL PICK-UP COIL COIL SWITCH INC

-BLK-H — PPL ORN -6RNH

dura-spark module

CONNECTORS

KEY O N POWER CRANK POWER

h RED-01- EZH3 m m - ] I-REP-

—blk o r blk/blu —c r y o r gry/blk—

s B

blr/cry o r blk/

SBEC

i—crn/blk

asd power in

Ftg 6-13. Ater grounding the ASO retry on this Chrysler igntton system, efwe* tor power at the cot! before a>ng ths tap test K the relay Is not workng, the tap test wont produce a spark

115

These replacement ignition wrts are constructed usmg high-grade sdicone that can withstand 500 degrees Fahrenheit, or under-hood temperatures They are avUaNe in either a carton impregnated fiberglass core for raito frequency interference (RR) sipprossion or a ptatod copper core tor racing Courtesy ot Mattery ignition and Summit Raclrsg Equtxnent

This Snap-On MT2S00 kV span* lestef can oe used on both convmoonal and OS igrntcn systems Flashing tIDs and a rotary uu indicate spark voiage tends

effect switch. If you didn'i get a spark, t h e power a n d g r o u n d wires at the power m o d u l e JII need to b e checked f o r correct values. Use a wiring diagram specific to the vehicle you arc w o r k i n g o n t o identify win-colons a n d correThe hgh energy igntson (HE!) upgradetottorGM rehxics uses an aicyd

s p o n d i n g clcctrical values. If the wires arc O K ,

dstnbutor cap mffi brass terminals These replacement parts exceed OEM

m o d u l e may be h a d .

power

speofKaDons Courtesy ot SummlfacingEqu