Automotive engine electronics  how to diagnose and repair the automotive computer control system

SECTION I -- Sensors & Systems SECTION II -- Driveability Diagnosis Background of Today's Automobile 9 Electrical & Electronic Terms 11 Point Style Ignition Systems 26 HE1 -- High E

repair the automotive

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Tai ngay!!! Ban co the xoa dong chu nay!!!

Automotive Engine Electronics

How to Diagnose and Repair the Automotive Computer

Control System

by Dr Robert C McElroy

Second Revised Edition

Accuracy Publishing, Homestead, Florida

photo by Rick Bernskoetter

Bob McElroy at the wheel of his Hilborn Fuel Injected Corvette at an SCCA autocross

Note video camera attached to windshield

Published by:

Accuracy Publishing Co

Post Office Box 514

All rights reserved No part of this book may be used or re-

produced or transmitted in any form or by any means,

electronic or mechanical, including photocopying, record-

ing or by any information storage and retrieval system

without prior written permission from the author except in

the case of brief quotations embodied in critical reviews

and articles

Copyright 1987,1988 by Robert C McElroy, Ph.D

First Printing 1987

Second Printing 1988, revised

Third Printing 1988, revised

Printed in the United States of America

Library of Congress Cataloging in Publication Data

McElroy, Robert C

Automotive Engine Electronics Understand, Diagnose & Repair: Fuel, Ignition

& Computer Control Systems

1 Automotive Electronics Computers, sensors, etc

2 Electricity and Electronics Computers, sensors, etc

3 Diagnosis Computers, sensors, etc

4 Mathematics Computers, sensors, etc

I Title

ISBN 0-929603-37-0 S o f t c o v e r

SECTION I Sensors & Systems SECTION II Driveability Diagnosis

Background of Today's Automobile 9

Electrical & Electronic Terms 11

Point Style Ignition Systems 26

HE1 High Energy Ignition 29

EST Electronic Spark Timing 3 1

Distributorless Ignition Systems CI 33

CCC Computer Command Control 35

EFI Electronic Fuel Injection 38

PFI Port Fuel Injection 40

Transition fuel to electronic systems 43

Throttle Position Sensor TPS 44

Temperature Sensors CTS & MAT 46

Manifold Absolute Pressure MAP 47

Electronic Spark Control ESC 48

Mass Air Flow Sensor MAF 49

Eshaust Gas Recirculation EGR 50

Idle Air Control IAC 53

Vehicle Speed Sensor VSS 54

Evaporative Emission Control EEC 55

Driveability Diagnosis Philosophy Systems Approach to Diagnosis Electronic Control Module ECM ALCL Terminal Circuits

Scanner Use Integrator & Block Learn Scanner Error

Diagnostic Procedures Digital Multimeter DMM Jumper Wires & Connectors Computer Harness Adaptive Tester Diagnostics & ECM Voltage Checks Continuity Tests

CHAT Basic Test Procedures CHAT Advanced Testing Procedures Advanced Circuit Testing

ECM Codes Open & Closed Loop Fuel Injector Balance Test

SELECTED ECM VOLTAGES &WIRE DIAGRAMS

Which can be read with CHAT

Note: CHAT will interface BCM and GMP4 design ECMs BCM and GMP4 circuits have not been included

in this publication CCC and EFI systems incorporating

"edgeboard" connectors were not included

CHAT is covered by U.S Patent No 4,690,475 and is available from Diagnostic Products Co

P.O Box 1136, Homestead, Fl 33090

Diagnostic Products Co is the Electronics Subsidiary of Spectra Investments Ltd Inc

Objectives of this manual:

1 Provide a comprehensive general explanation for electronically

spark controlled and fuel injected engines manufactured by GM

2 Provide specific information for the use of ALCL "scan" tools

3 Provide specific information for the use of "CHAT' the Computer

Harness Adaptive Tester

4 Provide specific information for the use of CHAT to perform voltage

and continuity testing for all wires and circuits interfacing the ECM

This manual has been prepared for:

1 Professional Technicians in the field of automotive repair

2 Students of Automotive Technology

3 Automotive Enthusiasts who wish to know more about

contemporary automotive engine electronics

This manual has been prepared with a "systems" approach:

1 Diagnosis and repair must be performed in a step by step method, to ensure

that you "isolate" the problem, and not simply replace what seems to be wrong

2 Automotive systems are broken down so that you can see how they are intended

to work in a conceptual method When you understand the general concept you will be able to apply your understanding to systems and components which differ from those included in this manual

This manual is not intended to replace applicable service manuals pertaining to the service of any automobile This manual is intended to complement service manuals specifically prepared by the vehicle manufacturer

In order to understand the complex na-

ture of today's automobile we must be

able to speak and understand the lan-

guage used to describe these vehicles

You may be reluctant to want to learn

anything, but you have made it this far by

purchasing this book A book which you

can use and learn new technology from

A book written to help you each and

every day on the job

Actually, when you start to dig into this

material it will be fun and interesting

The trick is to just take your time and

master these basic terms and concepts

One thing that you really need to do is

understand how these things work, at

least on a simple level This book will

approach everything on a simple level

and use this basic principle of under-

standing to build upon

Some of the things which we will look at

in the beginning will seem too simple to

really work with However, I have seen

too many repairs done incorrectly When

you really analyze what you are doing the

bottom line really must be to get the car

fixed Hopefully, this will happen the

first time or else you will have a recheck

to perform Rechecks mean that you will

not be making money on the next car

waiting for you Therefore, the fewer

rechecks the more money you ought to

make That seems simple enough,

doesn't it?

Always try and do the job right the first time even if it takes a few extra minutes One good example would be a water pump If it leaks then you will probably have to do the whole job over and I don't know of anyone who wants to redo a water pump The same sort of thinking applies to this new technology If the car still has a driveability problem then it is going to be a comeback and rechecks eat your earnings

NO RECHECKS

This book has been prepared with the

objective of presenting basic concepts

which apply to the modern automobile

which uses a small computer or ECM to

control fuel delivery to the engine In

order to understand how this system

functions, you will be presented the basic

concepts relating t o how air and fuel

management is accomplished

If you know and understand the relation-

ships between the sensor inputs and

computer outputs you will be able to

diagnose problems which occur with the

modern automobile No one book can

be expected to provide all information

which can apply to all situations How-

ever, the information provided will be of

value when you must diagnose and re-

pair these vehicles

As you gain experience with computer

equipped cars and trucks you will find

that they do perform and react in a

predictable way There are certain

things which you must know and under-

stand Some things must work or the

vehicle simply will not run These facts

will be covered so that you will be able to

quickly and accurately determine if

these necessary inputs are present Use

of a definite strategy will mean that your

diagnosis is done quickly and in a logical

procedure

Your use of a definite method of analysis will increase your productivity and reduce the number of comebacks and your number of rechecks This increase in productivity will make you a better tech- nician which should also correspond to an increase in your paycheck

In order that you understand how this system works we will first investigate the ignition system Understanding of today's ignition systems is 100% essential Proper fuel delivery to the engine is based upon this input signal and without it the vehicle will not run due t o loss of both spark and fuel delivery

NO WRENCHES ON THE RED TERMINAL

Always remove the ground cable first If you accidentally hit some sheet metal you will not

I believe that many technicians do not

have a good understanding of how igni-

tion systems operate Therefore, we will

study a conventional point-type ignition

first If you know and understand how

this system works you will not have any

difficulty with electronic systems More

cars are being designed each year without

distributors As you progress through

your study of this book, you will clearly

come to understand why a distributor is

not needed As you learn how these

systems operate and how other inputs

can provide the same necessary signal

you will be able to figure out and trou-

bleshoot systems which you have not per-

sonally worked on yet

As you study this manual and compare its

information to the cars which you work

with daily you will become a better tech-

nician Additional education at your

local technical school or community col-

lege will also help you to be more profes-

sional in your duties If you are not

already certified by ASE, you are encour-

aged to participate ASE certification is

a highly desirable goal and those techni-

cians who wear the ASE patch take pride

in their accomplishment You make your

living as a technician Vehicles which you

work on daily are highly complex and the

more you know about these vehicles the

better off you are Your need for techni-

cal literature and education have never

been greater You demonstrate your

professionalism when you wear the ASE

certification patch

YOUR TECHNICAL JOB

THE MORE YOU KNOW THE MORE THINGS YOU CAN FIX

FASTER &

MORE RELIABLE

EVERYONE BENEFITS FROM TECHNICIAN CERTIFICATION

SUPPORT IT!

I walked into my local Chevrolet dealer

and asked for a job as a junior mechanic

and grease monkey during my summer

break from college in 1969 That did not

last long; soon I was tearing apart engines

and trying to figure out how to get them

running again The more things which I

could fix, the more work I got in the shop

I drove my first race car in 1965 It was

while I was a senior in high school in State

College, Pennsylvania We even raced in

the winter I remember trying to run over

a snowbank during one event while rac-

ing on the icy surface This interest in

racing has probably been the key to why

I have always kept a strong interest in

automotives

Over the years I have raced many differ-

ent types ofvehicles including the likes of

jeep, ferrari, pantera, vega, corvair, mus-

tang, police cars, and my favorite, the

corvette Those police cars came from

when I taught High Performance Driving

to police officers at the Texas Transpor-

tation Institute

I have always felt that if you are going to

win on the track then you must field the

best car Even if you happen to be the

best driver around, if your machine is not

set up properly then you cannot win I

have never gone to an event with the idea

to lose Of course I don't always win and

I do get beat sometimes, but I don't lose

It really is a state of mind where you feel

confident about your ability and your

equipment When you know what you are supposed to do, and you do it well, then you can really enjoy what and how you do things I would hope that you personally feel that way about your occupation if you do not then I hope that this book will help you to gain this type of confidence

For a period of three years I was in the position of resident engine instructor, at one of the 31 G M training centers in operation at that time, after having been recruited by General Motors in 1983 In Detroit we would be given product infor- mation which would be used to conduct classes about new engine systems and their operation for dealership techni- cians who would attend our classes All this new information was great, but this information had to be passed on to the fellows and an occasional lady who actu- ally "turns a wrench" to make a living It really was a lot of fun

Additional qualifications to be your au- thor to write this book besides my expe- rience with GM, racing, and having been

a "Chevrolet Certified Technician" would include formal college education background of a BS, MA, and finally a Ph.D in industrial education from Texas

375 people inducted into the Automo- bile Hall of Fame in Midland, Michigan

as an "ASIA/ASE 'World Class' Techni- cian" for holding all 16 ASE area certifi- cations

Way back in the old days, pre-computer

cars that is, we basically concerned our-

selves with three types of problems: 1)

fuel, 2) ignition, or 3) mechanical How-

ever, today there is an additional 4) elec-

tronic problem area which really gives

technicians a tough time This latest

addition to our problems is the most dif-

ficult to understand You simply cannot

take apart a transistor with a 9/16" or

lOmm wrench Since you cannot easily

disassemble this electronic stuff it means

that you will probably have to learn about

these things either on your own or in a

class somewhere This book will help you

understand how automotive electronics

work and this book will help you fix

today's electronically complex cars

When cars were simple it was not too

difficult to figure out which area theprob-

lem was in and then it could be attacked

If there was a question about ignition,

then did spark come out of the plug wire?

If not then points were pretty easy to fix

I remember a 1970 LT-1 corvette at the

dealership, the ticket said "won't run" I

found the car, it would crank but not start

I popped off a plug wire and hung it on top

of the air cleaner wingnut; crank engine

again and no spark but the 12 volt test

light says power to the coil and a good

ground Hmmm the points must be locked up Off with the chrome shroud, remember this is a corvette, off with the distributor cap what the So much for

my first introduction to transistorized ignition

Today's cars may affect you the same way There is no denying that cars are much more complex than ever before and there is no alternative to under- standing how they operate Because of Federal regulations for improved fuel and emission characteristics of our ve- hicles it became necessary to develop more sophisticated engine control sys- tems to meet these new standards Many

of you reading this book look favorably

on the past but you know that "simple" cars are no longer built; also you know that the carburetor is in fact only a "cali- brated leak" which will not do the job today

Microprocessors are the heart of the computer or Electronic Control Mod- ule, ECM for short Microprocessors get information from many sensors placed all over the vehicle Microprocessors take this information and run it through the operational program recorded per- manently inside the machine found on

10

ROMS and PROMS After all this analy-

sis is done then some sort of output will

come from the ECM such as when to

inject fuel and how long the injectors are

to be held open

This entire information transmission

process at first seems almost impossible

to figure out However, this is not the

case There are some very logical rela-

tionships which d o exist and you as a

professional technician already know the

basic principles of engine operation We

will take these things which you are al-

ready familiar with and use them as the

basis for all the new systems New sys-

tems may be new but they accomplish the

same sort of things as the old systems

Whether or not new systems are better is

something which most mechanics and

technicians have personal opinions

about j ust ask one! Let's face it, there is

no alternative y ou have to know how the

new systems operate if we are going to be

successful in this occupation

How did you learn to be a technician in

the first place? Were you taught by other

mechanics or did you attend a technical

training program? I expect that you actu-

ally have some of both You have already

invested heavily in your education; some

people would call this the "School of

Hard Knocks." You have invested thou-

sands of dollars in your tool box Every

time the tool truck comes by you can

think of additional tools which will make

you more productive Tools are an in-

vestment in your future, there is no other

alternative there

When you finish reading this book you will find it to be an excellent reference

Others will want to use this book As with

any tool you will need to have it available

at times You know who borrows your

tools and this book is no exception A saying that I have seen on one master technician's toolbox is "I would rather

loan you my dog than my tools The dog always comes home." It applies to this book too

IF YOU WANT TO FIRE TWO SPARK PLUGS AT THE SAME TIME, HERE IS HOW IT'S DONE

First off let's look at wire With wire we

can "pipe" electricity to every device in

the car which needs energy to operate

Most wires in the car are made from

copper Some wires in the body harness

of the car are aluminum but these are

rare, and require special wire repair tech-

niques

Copper is a very good conductor A

conductor is a material which allows elec-

trons to flow through it easily If you are

going to keep the electrons in the wire

you must cover the wire with a tough

material which will not let the electrons

get out of the wire This material is called

an insulator Most wires are covered with

an insulator, which is generally a type of

plastic

Enough electrons moving will create an

electrical current How many electrons

you need to perform a job depends on the

load A crank or starting motor requires

INSULATION

Wires carry electrons Electrical pressure is called voltage Quantity of electrons is

measured in amps

a large electric cable cLming right-from

the battery, while a dome light needs only

a small wire to work effectively I

The electrical pressure to both the crank

motor and dome light are the same

Electrical Pressure is called VOLTAGE

Both items get the same voltage or pres-

sure coming from the battery because

12

wires conduct the electrons to each item

If the battery has a 12 volt potential

difference between the B + (red) and B-

(black) terminals at the battery and we

connect a wire to the B + and a wire to the

B- and then go to the end of each wire and

place a voltmeter between them we

should have 12 volts shown on the meter

If both the crank motor and the dome

light get the same electrical pressure then

why the different size of electrical wires

and cables? Both devices get 12 volts

The difference is how much work each

device must do That large cable to the

crank motor will allow many more elec-

trons to move than the small wire to the

dome light The quantity or amount of

electrons flowing is called AMPS

BAllERY VOLTAGE (PRESSURE) IS

INSUlATION

WIRE

AFTLIED TO B U M WRES!

If I had two cars, one with a 4 cylinder

engine breathing through a lbbl carbure-

tor and the other car had tunnel ram and

two Holley Double Pumpers then

which one will use the most fuel? The

tunnel ram will use the most fuel because

it needs that fuel to do its job properly,

just like the crank motor will need a lot

of amps to do its job properly If both our

cars use the same type of pump gas, then

in order to make more horsepower we

must deliver more fuel to the engine

Therefore we invest in the big 110 gallon

per hour electric fuel pump and use a I/

2" or larger fuel line between the fuel tank

and tunnel ram

If a fuel fitting leaks our car will not run

the way it is supposed to If an electrical

wire starts to corrode it will not conduct

current properly If a fuel line breaks the

car will not run If an electrical wire is cut

the component will not work If gasoline

spills and is ignited your car may be

destroyed If an electrical wire is shorted

to ground the electrical system and pos-

sibly the car might burn up

SHORT CIRCUIT

BRACKET HAS WORN THROUGH THE INSULATION ON THIS WIRE CAUSING A SHORT TO GROUND

Current, when flowing inside a good wire,

can be considered to have no resistance

to its flow Wires act as a pipeline of

energy to the item or component we need

to run When current cannot flow easily

to a component, resistance has been

added t o our circuit

Resistance in a wire is bad It generates

heat inside the wire and it means that not

enough current will get to the component

on the end of the wire The component

may not work properly because it does

not have enough current to perform

within its operating limits This reduc-

tion in current may cause the component

to fail

Resistance in a component means that

the item will perform work for us Imag-

ine you are holding a fire hose with water

spraying into the air If you aimed this

hose at the side of a mountain you would

start to wash away the mountain and the

stream of water would be doing work for

you The mountain becomes resistance

to the flow of water Work is performed

as you wash away the mountain

Each electrical item which performs

work in the car has some resistance

Resistance means that current cannot

simply flow right through the item to

ground The current must do something

which we want it to d o in order for the

current to get to ground This internal

electrical activity or flow will operate

each electrical component in the car for

US

DO NOT USE CRIMP CONNECTORS ON TODAY'S CAR

CRIMP CONNECTORS PROMOTE CORROSION WHICH CREATES RESISTANCE AND HEAT IN THE WIRE

Crimp connectors used for repair on this late model T Bird will create electrical problems for the rest of this car's life

Some components offer static resistance

to current flow and some items have

dynamic resistance to current flow If you

have ever taken apart a solenoid coil you

have found that there are many feet of

wire in the coil The length of wire and the

size of wire cause resistance inside the

coil This is an example of a static resis-

tance

Light bulbs and crank motors have dy-

namic resistance to the flow of current

When these items are working current

cannot get across them fast enough As

the armature moves past the brushes in

the crank motor, current flow is not con-

tinuous because current is directed to

different parts of the armature winding

because of the contact point placement

under the brush A crank motor which is

locked up can have a very high current

A mathematical relationship exists be-

tween volts, amps and ohms in any elec-

trical circuit George Simon Ohm discov-

ered the relationship between these fac-

tors and named the formula after him-

self, hence the name Ohm's Law

Mr Ohm found that volts or pressure in

a circuit will move a quantity of electrons

or amps through a defined resistance or

ohms This relationship means that if you

know any two of the three factors then it

is possible to determine the third item

mathematically

Although many technicians have diffi-

culty in learning Ohm's Law it is a very

important relationship which definitely

needs to be mastered Specifically, when

you know and can even visualize (yes

actually see in your mind) how these

three aspects of electrical flow work to-

gether then you will b e in a much better

position to f the modern car which uses

a microcomputer to control engine op-

eration

The Electronic Control Module or ECM

does everything electrically Voltage is

the language of the ECM Voltage is

pressure The ECM will control electri-

cal pressure to get things done Just like

you flip a switch to turn the lights on, the

computer will controlvoltage to a transis-

tor (functioning as an electrical switch) in

Ohm's Law Terms:

order to activate an output For example,

the air conditioning compressor clutch

which would be disabled during wide

open throttle to allow maximum accel-

eration

Ohm's Law will help you fix problem cars

The ECM is designed to handle only 1/2

amp on most circuits This means that the

relays and solenoids must have 20 ohm or

greater resistance or you will blow the

ECM Only "protected" circuits can

handle currents greater than 1/2 amp, an

example being the fuel injector solenoid

but this circuit is only pulsed in millisec-

onds (thousands of a second)

In a series circuit all the components or

devices are hooked up end-to-end This

arrangement means that all the current

(amps) in the circuit is the same through

BLOWER MOTOR RESISTOR BLOCK SERIES CIRCUIT DIAGRAM

each componenet used in the circuit

Current flow in a series circuit is like a

water hose All the water passes through

the hose from end to end In a series

circuit the same amount of current passes

through each component

SERIES CIRCUIT LAWS:

1 In a series circuit the current flowing in

the circuit is the same at all points in the

circuit

2 Total resistance of the series circuit is

the total of all individual resistances

present in the the circuit

3 The sum of all voltage drops, across

each resistance, in a series circuit equals

the applied or source voltage

MOTOR

w

Question: In a series circuit with three resistors, calculate the total

resistance (R T), and calculate the current flow using

Ohm's Law

12 VOLT wd

Step 2 determine total

Question Now that you know the amount of current flowing

calculate the voltage drop across each resistor using Ohm's Law

to determine voltaqe drop across each resistor

multiply amp flow times individual resistor values

E r l = 1 ~ = ~ I 1ampx2R = 2 w I t s

Er2 = I X R ~ = 1 a m p x 4 R = 4volts

Er3 = IxR3 = 1 a m p x 6 R = 6volts

total voltage drop = Erl + Et2 + Er3 = 2 + 4 + 6 = 12 volts

A parallel circuit has two or more

branches in which all the positive termi-

nals are connected to a common point

and all the negative terminals connected

to a common point Therefore, the same

voltage is applied across each compo-

nent

Parallel Circuit Laws :

1 In a parallel circuit, the voltage is

the same across each branch

2 Total current in the circuit is the

sum of the current flow in each branch

3 Total resistance of the parallel cir-

cuit is always less than the smallest

resistive branch

Maximum Panel Brightness

Set rheostat for O ohm

12 u is applied across each bulb

E

Ohm's Law equation I = w

I = elr I = 12vl2Oohm 1 6 amp {per bulb)

Amps total = amps per bulb x number of bulbs

Series - parallel circuits combine aspects

of both series and parallel circuits In the

series part of the circuit all the current

passes through one circuit component

In the parallel circuit there are multiple

paths for the current to pass through

In this example the rheostat is the series

load and the bulbs are the parallel load

To calculate current (amps) first deter-

mine the resistance of the parallel com-

ponents Add the parallel resistance to

the series resistance in order to deter-

mine total resistance Use Ohm's Law in

order to determine amp flow in this cir-

cuit

Voltage drop across series and parallel

segments can be determined by Ohm's

Law by multiplying amps times resis-

tance for the series segment

Total amp flow through bulbs

INSTRUMENT PANEL LIGHTING PARALLEL CIRCUIT DIAGRAM

DIODES

Diodes are devices which will allow elec-

tricity to pass through in only one direc-

tion DIODES are simply a ONE WAY

VALVE They allow current to pass

through in one direction and if the cur-

rent tries to reverse direction, then the

diode will block current flow

Alternators use nine diodes Six diodes

are in the rectifier bridge and three in the

diode trio These diodes turn the spin-

ning action of the alternator and its alter-

nating current (AC) into direct current

(DC) If any one of these diodes fail,

performance of the charging system will

be greatly affected

LIGHT EMITTING DIODES

Light Emitting Diodes or LED's are used

frequently in many automotive applica-

tions They are built like a regular diode

only they are designed to produce light

Whereas a regular diode made from sili-

con will require about 6v to turn on and

pass current, the LED needs 1.5 to 2 2 ~ in

most applications LED's are just like

regular diodes because they will not pass

current that wants to go against it

DIODE ELECTRICAL SYMBOL

DIODE CURRENT FLOW

LIGHT EMITTING DIODE

X X X X X X

WOUND STATOR

SINCE ALL THE CiJRRENT

I CONVENTW NAL

MUST PASS THRGUGH

THE CENTER CONNECTION

LESS OUTPUT RESULTS Y

5TATOR

ALTERNATOR OPERATION THROUGH EACH PHASE

TRACE CURRENT FLOW THROUGH DIODE BRIDGE IN EACH DIAGRAM

Diodes are also used to "bridge" sole-

noids Review of the information on

ignition systems shows in detail how the

primary coil builds up a strong electrical

field in the secondary coil, enough to fire

the spark plug when the primary coil is

turned off This condition is normal for

the many electrical coils and solenoids in

the car

Of special concern are the coils con-

trolled by the ECM Diodes are placed

across many coils They are installed in a

"reverse bias" position to block B + and

therefore the current passes through the

coil When B + is turned off the magnetic

field of the coil collapses inducing cur-

rent flow in the coil This current then

passes through the diode, since this cur-

rent is headed in the same direction as

the diode arrow, which was previously

blocking B + and thus this current flow

induced by the electric field of the coil is

allowed to "collapse upon itself' A

spark is not produced and the delicate

ECM is protected against damage

Even small coils, found in simple relays,

can produce over 100 volts when they are

turned off Large air conditioning clutch

coils can produce 60v to 130v with much

greater amp flow Higher voltages are

produced with quicker clutch return

times You will see this despiking diode

connected to and taped over, on the elec-

trical plug attaching to the ac compres-

sor

A / C COMPRESSOR CLAMPING DIODE

CURRENT CONTINUES TO FLOW THROUGH THE CLAMPING DIODE UNTIL THE COMPRESSOR FIELD COLLAPSES UPON ITSELF

Transistors are simple little devices when

you understand how they do in fact work

The best way to understand them is to

first look at a simple old light switch on

the wall You flip the switch up and the

light goes on You flip it down and the

light goes off Now if I tell you that the

transistor works exactly the same way as

the light switch, only electrically, and that

instead of manually pushing the switch

you need only send a little voltage to it in

order to turn the light on, then we've

almost got it licked

Look at the diagram on the NPN transis-

tor Notice that the main current path is

from top to bottom Coming in from the

side is the small current path necessary to

turn on the large current flow This

means that you could use a very small and

light duty switch to turn on a high current

requirement accessory It only takes 6v

to turn on the average transistor

Transistors function as switches and they

can function as a flow control valve Now

that we have the transistor turned on, if

we want to let more current flow through

it, top to bottom, then we simply apply

more voltage to the base When the

transistor is at "saturation" it is allowing

all the current through it is designed for

Drive it beyond saturation and it will be

destroyed 9,000 rpm with your street

motor won't work However, a little

voltage change on that base lead will be

just like your foot on the accelerator

N P N TRANSISTOR

NPN TRANSISTOR Nclativc

POSI~~VC

Ne jativc Semiconductor nternal cm~tructim

POINT SET

-

-

POINT TYPE I G N I T I O N SYSTEM

out over early magneto systems If you

understand how the point system works

you will be able to service millions of

different cars, but they all work the same,

even if the actual components are differ-

Point type ignition systems were the stan-

dard ignition method for cars by winning

ent

Refer t o the picture and find the 12 volt

little resistance to current flow, but when the current does flow it sets up a

source Let's follow our current through

the system and see what actually goes on

First the current flows through the Pri-

mary Ignition Coil, which is composed of

large diameter wires to allow lots of amps

through If you were to check a primary

ignition coil with an ohmmeter you will

probably find about one ohm of resis-

tance One ohm means that there is very

large electromagnetic field around the coil (see page 13) This electromagnetic field is essential to the operation of the coil because it will induce current into the Secondary Ignition Coil later on, but for now this magnetic field is just building up in strength

Now that the current has passed through the primary coil it heads onto the Contact Point assembly In fact it goes all the way to the Top contact point, as shown in the diagram The top contact point always will be hot If you took a voltmeter and touched it to the top point you would see 12 volts

If you have ever installed o r held a set of

points you know that there is a spiral

spring used to bring the contact points

together In order to separate the points

the rotor lobes must be positioned, in

relation to the rubbing block on the point

locator arm, so that the points will alter-

nately open and close as the rotor turns

Since the top point is always electrically

hot, whenever the points come together

current will flow across to the bottom

point and thus to ground completing the

circuit Many amps will then flow

through the primary ignition coil rapidly

buildingtheelectromagneticfield around

both primary and secondary coils

Since the rotor is generally driven by the

camshaft it will continue to turn A lobe

of the rotor will begin to rise, eventually

pushing the top point away from the

bottom point At that time the primary

coil will be turned off since current can no

longer flow through the primary coil

The Electromagnetic Field which was

built up around both the primary and sec-

ondary coil will start to collapse This

field is made up of "magnetic force lines"

which will start to fall back upon the

primary coil These lines of magnetic

force will attempt to push current

through the primary coil to keep the

current flowing sort of like lifting your

foot off the gas while driving at 50 mph,

the car will continue to coast since you

have already built up speed and momen-

tum

These magnetic lines of force try to do the

same thing only electrically However, in

27 the process of collapsing they cut across the secondary ignition coil winding and begin to induce electrical pressure in this coil The secondary coil can have 6,000 to 14,000 ohms resistance which means that

it is a very long coil of wire and the collapse of the electromagentic field will cut across a lot of wire length

This is exactly what happens and the electrical pressure built up in the secon- dary coil becomes so great that it will eventually jump a large air gap The air gap of course will be on our spark plug, igniting the engine air fuel mixture at just the right time to make for good power and driveability

CAPACITOR

This is a good time to look at the "electri- cal shock absorber" or capacitor Let's go back to the primary ingition coil for a minute and look at what's happening When the contact points close current passes through the primary coil and on through the contact point set to ground When the points are pushed apart the circuit is broken and the electromagnetic field will start to collapse inducing elec- trical pressure strong enough in the sec- ondary coil to fire the spark plug What about the primary coil it will have an induction also

Imagine the points just opening, many electrons will be hurriedly moving along; just like that car at 50 mph Your car might "stop on a dime" but I would guess that a lot of skid marks would result if you locked up the brakes all the way to a

28

"dead stop," then you would need to go

buy some new tires because of the flat

spots If you haven't tried this just ask

some of the guys at your service facility;

I'm sure that there is someone there who

has destroyed some perfectly good tires

by locking up the brakes Of course the

best way to stop is to use the brakes, that's

why a car has brakes

Electricity flowing in the coil needs a way

to stop without "crashing out." Such is

the job of the capacitor, it provides a "run

off area" or another path for this electric-

ity to go Have you ever been to the

mountains and noticed "truck run offs"

which are large sand pits that 18 wheelers

can head into if their brakes quit while

going downhill A capacitor is exactly the

same thing, an electrical run off with no

escape other than go back out the way the

current originally came in

When the points close many electrons

will start moving When the points open

these electrons will build up tremendous

pressure on the top point as they all try to

keep on moving If we add a capacitor

then the electrons will electrically take

the capacitor for ground and head off

into the capacitor A capacitor is a "false

ground" in this application because the

electrons cannot actually get to ground

they only think that they can The capaci-

tor will use a large internal surface area

or "plate" wrapped up inside it, posi-

tioned very close to another "plate"

which is attached to ground Thus the

electrons think that they can get to

ground by going through the capacitor

As more and more electrons enter the

capacitor it will build up electrical pres- sure and start to build up resistance to the other electrons which are also headed into the capacitor When the electrical pressure gets higher than that of elec- trons trying to get in, then electrons will flow back out of the capacitor Thus the similarity to the shock absorber give-and- take

If you have ever wondered about those bumpy little lines on an ignition oscilloscope well now you know Those funny lines are the electrons bouncing back and forth because of the capacitor

If the capacitor is bad then you will burn out the points because instead of just sparking the spark plug you will also spark the points and they will simply burn

UP

Capacitors are used in many applica- tions They reduce alternator hum in the radio They are used any place that electrical pressure (voltage) fluctuates and you need to smooth things out Nothing is supposed to go through them, unless it's been blown out They normally seem to work quietly and forever until it quits and something burns up

4 CYLINDER MAGNET I C TRANSISToR PICKUP C O I L

VOLT

HIGH ENERGY I G N I T I O N SYSTEM

Now that we know how a set of points

work we can move into HE1 which is

really a logical progression of ideas and

technology In review, we know that the

points close allowing the primary coil to

build up an electromagentic field which

collapses when the points open inducing

electrical pressure (voltage) into the

secondary coil which causes the spark of

the spark plug

HE1 works the same except that a tran-

sistor is used instead of points Since the

transistor is electronic it won't burn up

like a set of points I didn't say it

wouldn't burn up, I'm sure that you can

destroy anything but that's not the

point Anyway, the idea is that a transis-

tor will not need as much attention or maintenance as the points Now all we have to do is turn the transistor off and on and everything will be great

If you haven't read the section on transis- tors stop here and go do it This book is designed with the KISS method, meaning Keep It Simple Stupid and your author thinks that you better understand how this mess works with the easy stuff first I didn't say-I was easy, I said that it was going to

be explained simply If you do not under- stand how point ignition systems work or you do not understand how the transistor works, then do yourself a favor and go back to these systems now for review HE1 can be simple but it will only be simple if

30

you understand the basics Have you ever

seen a 440-T4 transmission pulled all the

way down? It will cover every workbench

in the shop I can overhaul a turbo 400

but I would not even want to think about

the 440-T4 What does this have to do

with HEI? As a wise man once said (he

was with the World of Outlaws, the sprint

car association) "if you're going to run

with the 'big boys' you better come pre-

pared." Moral of the sto ry don't try to

fix something you don't understand and

you can't fix something that's not broke

In order to make the HE1 transistor work

all we need do is to provide it with a small

voltage to turn the primary coil on This

small voltage comes from the Magnetic

Pickup assembly which now replaces the

rotor of our point ignition system Have

you ever noticed how magnets react to

each other? Either you cannot pull them

apart or you cannot push them together,

no matter how hard you try

Now we've got HE1 licked Put a star

magnet on the distributor shaft and put a

magnetic ring outside it When the dis-

tributor shaft spins the magnets will pro-

duce an alternating current Take this

current and pass it through a diode and

now we have pulsating DC because half

the original AC is blocked Now add the

Zener diode and we have a nice square

wave produced which will make that

transistor work just like a set of points

To get the HE1 right for your engine the

magnetic pickup needs to have the same

number of star points as the number of

cylinders in your particular engine

L-

4 Terminal HE1 Module

Therefore: 4 star = 4 cylinder, 6 star = 6 cylinder, or 8 star = 8 cylinder

If this explanation makes sense to you then you will be well prepared to deal with any electronic ignition system Making the primary coil work will be the function of a power transistor Making the power transistor work will be a func- tion of some sensor The pickup sensor may be magnetic, hall effect, or optical However there must be some sort of pickup mechanism Once you have the general electronic ignition system fig- ured out you should be able to diagnose most problems by referring to specific information provided by the manufac- turer of the subject ignition system

Remember, what we are dealing with in this book are general concepts which will help you diagnose problems This type of information is universal and therefore it can be applied each and every day to your work You have special tools in your tool box which you seldom use This informa- tion is valuable each and every day as you approach new problems To fii the car is one thing To understand what was wrong with it and then be able to fi it is much more difficult

HIGH ENERGY I G N I T I O N SYSTEM

WITH ELECTRONIC SPBRK T I M I N G

With advent of the on board computer or

ECM, mechanical and vacuum advance

could be eliminated The computer

could simply look at its sensor values and

determine what it wanted to do with

ignition timing

In order to get this system to work we

simply change the routing of the signal

from the original HEI When the engine

starts the HE1 works like normal, as we

have looked at, with the magnetic signal

going to the transistor to operate the

primary ignition coil When the engine

reaches 500 rpm the computer will apply

5 volts to energize the bypass coil The bypass coil pulls the relay control arm over to the Electronic Spark Timing contact and this signal is then fed to the power transistor

Inside the ECM there is a signal linking between reference and EST Hence, when the reference signal is received the ECM knows t o send out an EST signal If reference is lost the engine will stop running Why? Send no signal to the ECM and it will think that the engine is not running so no signal will be sent out

to the power transistor

Engine Starts on

Base Timing

ECM EST

Rclcrcncc -)

Bypus

Ground

h 1

During crank and until

500 rpm the engine runs

on Base Timing, just like standard HEI

During the 1982 model year G M ignition

modules for this type of ignition system

began incorporating an internal resistor

at the end of the EST contact This was

done so that the ECM could send a circuit

checking voltage down the wire before

EST was engaged Otherwise, if the EST

circuit was open or shorted to ground the

engine would stall when EST was cycled

on by the ECM This circuit check is now

performed before EST is engaged Be-

fore this feature became standard the en-

gine would stall when EST was engaged

This start and stall cycle would happen

repeatedly On carburetor equipped cars

you could disconnect the 4 wire connec- tor of the distributor and the car would continue to run because then the 5 volt bypass signal would not be applied to the module

On EFI' and PFI cars if you jumper to-

gether the A to B connectors in the

ALDLyou should notice a change in rpm

to show you that the EST is working G M diagnostics say to do this at 2,000 rpm but you can notice the rpm difference at idle

D o not drive the car with A to B jumpered

together, you can burn the car up For more on this subject refer to the scanner and how it affects the car

You really don't need a distributor, you

only think that you need it Let's think

about this a minute and maybe it will not

seem quite so bad At first it really

bothered me that the distributor was

gone but then I realized that it wasn't any

good to me and that if it was eliminated

then I would have one less thing to take

up space on top of the engine

As for the basic idea, well let's start with

the distributor shaft It is powered by the

camshaft With the pole piece creating

the control signal for power transistor of

the HE1 module If a Hall effect sensor

were hooked to the harmonic balancer

then the spinning crankshaft would give

us the best indication of exactly where the

crank is However, since the crank goes

around twice for every revolution of the

camshaft we must fire two cylinders at the

same time in order to get the engine

working properly, which is how it works

The only trick is to get the coils started off

in the right sequence and then the elec-

tronics will keep everything working

right This initial signal can come from

several places such as using a double Hall

effect sensor on the balancer with one

having only one vane to electronically

signal the start up sequence and then the

regular vaned sensor can provide the

control signal to operate the coil packs

For many six cylinder engines a 3 vaned rotor is mounted on the back side of the harmonic balancer When these vanes pass through the Hall Effect sensor

a square wave signal is produced Each vane is dedicated to only one coil pack which will fire two spark plugs at one time The cylinder on compression and the cylinder on exhaust

These crank generated signals provide the same information to the ECM as it would receive from the magnetic pickup

in a standard HE1 only now we do not need the distributor to generate these signals

c31 COMPUTER CONTROLLED COIL IGNITION

3 VANES ARE MOUNTED O N

THE BACK SIDE OF THE BALANCER EACH VANE CONTROLS ONE COIL

SQUflRE WflUE PRODUCED BY HflLL EFFECT SENSOR

I S SENT TO THE ECN I S ENGINE REFERENCE SIGNIL

Federally mandated Corporate Average

Fuel Economy or CAFE standards set

minimum emission requirements and

fuel economy requirements GM deter-

mined that the traditional carburetor

system could no longer get the job done

of controlling the air / fuel mixture

Computer Command Control or simply

CCC could adequately meet these legal

standards CCC put a computer in the

average automobile

A small on-board microcomputer was

selected to perform the task of keeping

watch on the air / fuel mixture Specifi-

cally, this microcomputer called an Elec-

tronic Control Module or simply, ECM is

intended to watch what happens in the

exhaust pipe and use this reading to

meter fuel into the engine

The basic principle is straightforward

Monitor engine exhaust in order to con-

trol fuel delivery This is the operational

principle behind every automobile

manufacturer's system relating to air /

fuel control in order to meet applicable

fuel and emission standards

In order to make this control system work

it seems that just about everything under

the hood and on the engine had some sort

of computer wire coming out of it

Making a carburetor into a precision

metering device seemed like a good idea

at the time

CCC Carburetor is an expensive and com- plex device Special training and special tools are necessary before making any adjustments to this type of carburetor

A regular carburetor (no wires coming out of it) will have metering jets or orifice

to allow fuel to pass through in order to get into the airstream going into the engine CCC carburetors can control fuel flow through the jets

CCC carburetors (look for the wires) have a Mixture Control solenoid or MC solenoid inside the carburetor which can

be turned on and off by the ECM When the M C solenoid is turned on fuel deliv- ery is restricted and the engine will run lean When the solenoid is off the engine will run rich Pulsing of the M C solenoid

is the sound you hear coming from under the hood of the car when you turn the ignition key on

Let's look at what happens when the MC

solenoid is energized so we can under-

stand exactly what the ECM is trying to

do First off, the solenoid runs hot,

meaning that it is wired to B+ and then

all the ECM needs to do is ground the

wire and the solenoid will be energized

This ECM controlled switch is called a

"Driver" or "ECM Driver"

When the ECM grounds this circuit,

current flow energizes the MC solenoid

An electromagnetic field is developed

This field pulls down a metal plate, about

the size of a postage stamp, mounted just

above the solenoid inside the carburetor

This plate is normally held up by a high

' quality spring

When the plate comes down two things

happen Fuel is reduced because the

metering rods are pushed down into the

main metering jets and an idle air bleed

is opened which allows air access be-

tween the idle tube and a fuel channel

restriction In simple terms when the

solenoid goes on fuel is reduced and air is

dumped in

This combined action will make a big

difference between rich and lean condi-

tions and gives the ECM a wide range of

control over engine operation This book

will not attempt to get into specific ad-

justments for any carburetor, only to

provide a general theory of operation

Overhaul and adjustment of carburetors

is a science by itself

A n oxygen sensor is placed in the exhaust

Close up internal view of CCC carburetor Clearly visible are rich and lean stops for Mixture Control (MC) solenoid MC solenoid

is energized in this picture

gas stream so that it can get a reading on the amount of' oxygen in the exhaust

SENSES OXYGEN An oxygen sensor

is a voltage generator, it makes voltage chemically that is correct The oxygen sensor is a sophisticated device which uses several exotic metals which will produce electricity when heated in the presence of oxygen

Let's look inside this sensor It screws into the exhaust so exhaust gasses can pass over the face of the sensor The sensor is hollow so that normal air can get

to the inside of the sensor When the sensor gets hot a voltage is produced because of the difference in oxygen con- tent of the two air surfaces

For instance, if the sensor were simply

hot and hanging out on the end of a rope

in the middle of the shop then the oxygen

content of the air inside and outside the

sensor would be the same with no differ-

ence in oxygen content, thus no voltage

Now back to the car With exhaust gases

going over the sensor there is a difference

in oxygen content between the two air

masses If you add more fuel you will

have less oxygen in the exhaust stream

because it will have been burnt up in the

combustion process If you remove fuel

then you will have more oxygen in the

exhaust stream The greater the differ-

ence in the oxygen between the two then

the greater the voltage produced

Oxygen sensors are designed to produce

voltage over a range of l to .9 volt They

are designed with a 45 volt mid range or

center If a voltage greater than 45 is

produced the engine is said to be rich, all

the oxygen has been burnt up Less than

.45 volt and the engine is lean, because

there is a lot of oxygen in the exhaust

stream which has not been burnt up

The ECM will adjust the on time of the

MC solenoid so that the oxygen sensor

voltage "toggles" or pivots around 45

volt If the ECM cannot do this job

properly then the Check Engine or Serv-

ice Engine Soon light will come on and a

Code will be set for the rich or lean

condition which the ECM cannot cor-

rect

THE OBJECTIVE 15 TO MAINTAIN

2 ) FUEL ECONUMY

Electronic Fuel Injection is one of the

best systems to come along in the history

of automotive technology It is simple,

precise and reliable EFI is a "single

point" fuel delivery system meaning that

all the fuel to the engine is supplied from

a central location by one or two fuel

injectors

Using the reference signal to the ECM

provides accurate information about

crankshaft position and engine rpm

Each time the ECM receives a reference

signal the ECM will pulse the fuel injec-

tor This means that short pulses of fuel

are delivered into the intake manifold at

the same point as the carburetor used to

be placed Each pulse of fuel will be

metered to provide the necessary fuel for

each cylinder needing an air and fuel

charge

If you take a timing light and hook it to

the ignition coil wire you can see the fuel

CADILLAC HT-4100 USES A DUAL THROlTLE BODY FUEL INJECTOR

REFERENCE SIGNALS ARE RECEIVED BY THE ECM

pattern delivered from the fuel injector

If you push the Throttle Position Sensor

or TPS down with the timing light in-

stalled, you will see extra pulses of fuel

being delivered since the ECM interprets

this action as acceleration Since you do

not have an accelerator pump then you

will need this extra fuel to prevent a

possible tip in hesitation If you put a

vacuum pump on the Manifold Absolute

Pressure sensor or MAP sensor you can

cause the engine to stall because fuel

delivery can be cut back or cut off en-

tirely The ECM will interpret this high

vacuum as high deceleration with closed

throttle

If you spend time around the circle track

you know that carburetors have to be

rebuilt several times a season because the

gaskets are simply sucked into the carbu-

retor Imagine how the racing carburetor

will go wide open down the straights and

then at high rpm have the throttle valves

snapped shut as the car slows for the

corner lap after lap The ECM says that

with high vacuum in the intake manifold

and with low TPS voltage that you do not

need fuel, so the injector is simply not

turned on at all

EFI generally works in a Synchronous

mode, meaning that for every reference

pulse you get a shot of fuel However, it

can also work in an Asynchronous mode

under acceleration or deceleration when

synchronous fuel delivery just will not do

the job right Another example of asy-

chronous fuel delivery occurs with Prime

Pulses which occur on some engine sys-

tems Prime pulses occur with a cold

DUAL THROlTLE BODY INJECTORS ARE USED ON MANY DIFFERENT TYPES OF 6 AND 8 CYLINDER ENGINES ALL SYS- TEMS WORK VERY SIMILAR THE DUAL THROlTLE BODY "CROSSFIRE" ALSO ALTERNATELY PULSES EACH INJECTOR

AIR LEAKS CAN RESULT IF THE TOP "0" RING LEAKS FUEL LEAKS CAN RESULT

IF THE BOlTOM " 0 " RING LEAKS

engine to get it started Since you do not have an accelerator pump to provide that extra fuel to get the car started in cold weather prime pulses will be delivered before you start cranking to get fuel into the engine The ideal airlfuel ratio for the engine is 14.71b of air to 1 lb of fuel when the engine is warmed up When the engine is cold, 20 below zero, then 1.5 to

1 is the ratio Carburetors have chokes,

EFI likes asynchronous prime pulses