`
`VW EX1022
`
`US. Patent No. 6,588,260
`
`VW EX1022
`U.S. Patent No. 6,588,260
`
`

`

`Copyright © 1989 by Harcourt Brace Jovanovich, Inc.
`
`All rights reserved. No part of this publication may be reproduced or
`transmitted in any form or by any means, electronic or mechankal,
`including photocopy, recording, or any information storage and re(cid:173)
`trieval system, without permission in writing from the publisher.
`
`y
`
`Requests for permission to make copies of any part of the work should
`be mailed to:
`Permissions, Harcourt Brace Jovanovich, Publishers,
`Orlando, Florida 32887.
`
`ISBN 0-15-504355-2
`
`Library of Congress Catalog Card Number 88-83243
`
`Printed in the United States of America
`
`

`

`CONTENTS
`
`Chapter 1
`THE NEED FOR ELECTRONIC CONTROL
`OF ENGINE OPERATION, 1
`
`1-1
`1·2
`1·3
`
`1·4
`
`Primary Engine Controls, 2
`Secondary Engine Controls, 3
`Legislated Fuel Economy
`Standards, 4
`Electronic Control System, 5
`Chapter Review, 9
`
`Chapter 2
`ELECTRICAL FUNDAMENTALS, 11
`
`2-1
`
`2·2
`2·3
`
`Structure of Matter
`and the Atom, 12
`Electron Theory, 14
`Electrical Current, Voltage,
`and Resistance, 15
`Ohm's Law, 17
`2·4
`Electrical Circuits, 18
`2·5
`2·6 Magnetism, 20
`Electromagnetism, 22
`2·7
`Electrical Control Devices, 28
`2-8
`2-9 Wiring Diagrams and
`Symbols, 32
`Chapter Review, 34
`
`Chapter 3
`ELECTRONIC FUNDAMENTALS, 37
`
`Chapter 4
`AUTOMOTIVE MICROCOMPUTERS, 55
`
`Chapter 5
`TEST EQUIPMENT AND PROCEDURES,
`85
`
`3·1
`3·2
`3-3
`3-4
`3-5
`
`Semiconductors, 38
`Diodes, 40
`Transistor, 43
`Capacitors, 46
`Integrated Circuits, 49
`Chapter Review, 53
`
`4·1 Microcomputers, 56
`4-2 Microcomputer Input Signals, 58
`4·3 Microcomputer Input Signal
`Sources, 60
`Processing Information, 70
`4·4
`4-5 Microcomputer Output
`Devices, 76
`4·6 Microcomputer Open and Closed
`Loop Control, 80
`Chapter Review, 83
`
`5·1
`5·2
`5·3
`
`Electrical Test Instruments, 86
`Voltmeters, 88
`Ammeter, 89
`
`IX
`
`

`

`~ .......... ----------------~
`
`x
`
`CONTENTS
`
`Chapter 6
`FORO ELECTRONIC IGNITION SYSTEMS,
`117
`
`Chapter 7
`TESTING TYPICAL FORO ELECTRONIC
`IGNITION SYSTEMS, 145
`
`Chapter 8
`CHRYSLER ELECTRONIC IGNITION
`SYSTEMS, 177
`
`5·4
`5·5
`
`5-6
`
`Ohmmeter, 90
`Continuity Testers and Jumper
`Leads, 92
`Engine Performance Test
`Equipment, 95
`5·7 Microcomputer Engine Control
`System Testers, 102
`Specifications, Diagrams, and
`Diagnostic Charts, 105
`General Safety Precautions, 111
`Chapter Review, 113
`
`5·8
`
`5·9
`
`6·1
`
`6·2
`
`6·3
`
`6·4
`
`6·5
`
`6·6
`
`6-7
`
`6·8
`
`7-1
`
`7·2
`
`7-3
`
`7-4
`
`Negative Characteristics of
`Standard Ignition Systems,
`118
`Ford Transistorized Ignition
`System, 122
`Ford Solid State Ignition
`System, 123
`Ford Duraspark I Ignition
`System, 127
`Ford Duraspark II Ignition
`System, 130
`Ford Duraspark III
`Ignition System, 133
`Ford Thick-Film Integrated-!
`Ignition System, 137
`Ford TFI-IV Ignition System,
`140
`Chapter Review, 143
`
`General Precautions, Test
`Equipment, Calibration Codes,
`and Troubleshooting Guides,
`146
`Testing SSI and D\ll'aspark
`II Systems, 150
`Testing a Ford Duraspark
`III Ignition System, 163
`Testing a Ford TFI-IV Ignition,
`171
`Chapter Review, 175
`
`8·1
`
`8-2
`
`Design and Operation of
`Chrysler Electronic Ignition,
`178
`Conventional Advance
`Mechanisms, 183
`Hall-effect EIS, 184
`8·3
`8·4 Mitsubishi EIS, 185
`a-5
`Chrysler Electronic Lean
`Burn System, 186
`Electronic Lean Burn
`System Operation, 189
`
`8-6
`
`

`

`Chapter 9
`TESTING TYPICAL CHRYSLER
`ELECTRONIC IGNITION SYSTEMS, 199
`
`Chapter 10
`GENERAL MOTORS ELECTRONIC
`IGNITION SYSTEMS, 221
`
`Chapter 11
`TESTING TYPICAL GENERAL MOTORS
`ELECTRONIC IGNITION SYSTEMS, 243
`
`Chapter 12
`COMPUTERIZED AIR INJECTION
`SYSTEMS, 263
`
`CONTENTS
`
`xl
`
`8-7
`
`8-8
`
`8·9
`
`9-1
`
`9-2
`
`9·3
`9-4
`
`9-5
`
`10-1
`
`10-2
`
`10-3
`
`10·4
`
`11-1
`
`11-2
`
`11-3
`
`11-4
`
`11-5
`
`12·1
`
`12-2
`
`12-3
`
`12-4
`
`12-5
`
`Electronic Spark Control
`System, 192
`Electronic Spark Advance
`System, 192
`EFI Spark Control System, 193
`Chapter Review, 196
`
`General Precautions and
`Test Equipment, 200
`Testing a Chrysler Electronic
`Ignition System, 201
`Testing a Hall-effect EIS, 205
`Testing an Electronic Lean
`Burn System, 208
`Testing an EFI Spark Control
`System, 215
`Chapter Review, 218
`
`Design and Operation of the
`HEI System, 222
`Electronic Spark Timing
`System, 229
`Electronic Spark Control
`System, 235
`Distributorless Ignition
`System, 235
`Chapter Review, 241
`
`General Precautions and
`Test Equipment, 244
`Testing a TYpical HEI
`System, 245
`Testing a TYPical HEI, EST
`System, 249
`Testing a TYPical HE!, ESC
`System, 252
`Testing a TYPical DIS
`System, 257
`Chapter Review, 261
`
`Function of the Air
`Injection System, 264
`Design of a Basic Air
`Injection System, 265
`TYpical Ford Computerized
`Air Injection, 270
`TYpical Chrysler Computerized
`Air Injection, 277
`TYpical General Motors
`Computerized Air Injection,
`278
`Chapter Review, 282
`
`

`

`xll
`
`CONTENTS
`
`Chapter 13
`TESTING A TYPICAL AIR INJECTION
`SYSTEM, 285
`
`Chapter 14
`COMPUTERIZED EGR SYSTEMS, 295
`
`Chapter 15
`TESTING A TYPICAL COMPUTERIZED
`EGR SYSTEM, 313
`
`I
`
`Chapter 16 ,
`TYPICAL COMPUTERIZED
`EVAPORATION AND EFE EMISSION
`CONTROL SYSTEMS, 325
`
`13-1
`
`13·2
`
`13-3
`
`13-4
`
`13-5
`
`13·6
`
`14-1
`
`14-2
`
`14-3
`
`14-4
`
`14·5
`
`15·1
`
`15·2
`
`15-3
`
`15·4
`
`16·1
`
`16-2
`
`16·3
`
`16·4
`
`16·5
`16-6
`
`Checking the Drive Belt
`and Air Pump Operation, 286
`Testing a Typical Diverter
`Valve, 288
`Testing a Typical Combination
`Valve, 289
`Testing the Check Valve and
`Air Manifold, 290
`Testing an Electric Solenoid
`and Its Circuit, 291
`Testing an Air Injection System
`for Excessive B ack Pressure,
`292
`Chapter Review, 294
`
`Function of an EG R
`System, 296
`Design of a Bask EGR
`System, 297
`Typical Ford Computerized
`EG R System, 300
`Typical Chrysler Time-Delay
`and Computerized EGR
`Systems, 304
`Typical General Motors
`Computerized EGR System,
`307
`Chapter Review, 310
`
`General EGR System
`Service, 314
`Testing the Operation of an EGR
`System, 316
`Testing Venturi Vacuum and
`Time Delay Systems, 318
`Checking Computerized System
`Components, 321
`Chapter Review, 324
`
`Purpose and Types of
`Evaporation Emissions
`Control Systems, 326
`Design of a Typical EEC
`System, 327
`Carburetor Float Bowl
`Vent Controls, 331
`Computerized Canister
`Purge Control, 332
`Need for the EFE System, 333
`Design and Operation of
`EFE Systems, 335
`Chapter Review, 337
`
`

`

`Chapter 17
`TESTING AND SERVICING TYPICAL
`EVAPORATION AND EFE SYSTEMS, 339
`
`Chapter 18
`FORD COMPUTERIZED ENGINE
`CONTROL SYSTEMS, 349
`
`Chapter 19
`TESTING A TYPICAL FORD EEC-IV
`SYSTEM, 391
`
`Chapter 20
`TYPICAL GENERAL MOTORS
`COMPUTERIZED ENGINE CONTROL
`SYSTEMS, 41 5
`
`Chapter 21
`TESTING TYPICAL GENERAL MOTORS
`COMPUTERIZED ENGINE CONTROL
`SYSTEMS, 459
`
`:
`>.
`
`CONTENTS
`
`XIII
`
`17-1
`
`17-2
`
`17-3
`
`17-4
`
`18-1
`18-2
`18-3
`18-4
`18-5
`
`19-1
`19-2
`19-3
`19-4
`
`19-5
`
`20-1
`
`20-2
`20-3
`
`20-4
`20-5
`
`21-1
`
`21-2
`
`21-3
`
`21-4
`
`21-5
`
`21-6
`
`Inspecting and Servicing
`'l)rpical EEC System
`Components, 340
`Computerized EEC System
`Component Vacuum and
`Electrical Tests, 343
`Inspecting and Servicing
`the Heat Control Valve
`EFE System, 344
`Testing the Heat Grid
`EFE System, 346
`Chapter Review, 348
`
`Ford EEC-I System, 350
`Ford EEC-II System, 357
`Ford EEC-III System, 364
`Ford EEC-IV System, 369
`Ford MCU System, 380
`Chapter Review, 388
`
`Diagnostic Routines, 392
`Service Codes, 394
`Types of Service Codes, 398
`EEC-IV Quick Test
`Procedures, 401
`Pinpoint Test Routines, 409
`Chapter Review, 410
`
`Computer Command Control
`System Inputs, 416
`CCC System Outputs, 424
`CCC Microcomputer and
`System Operation, 436
`CCC-TBI System, 439
`CCC-PFI System-Domestic
`and Imported, 451
`Chapter Review, 456
`
`General Service
`Information, 460
`CCC-Carbureted System
`Diagnosis, 465
`Diagnosing Symptoms of
`Driveability Complaints, 473
`Diagnosing Driveability
`Problems with Trouble
`Codes, 474
`Using Diagnostic Charts
`Without Trouble Codes, 475
`Diagnosing TBI and PFI
`Systems, 475
`
`

`

`xlv
`
`CONTENTS
`
`Chapter 22
`TYPICAL CHRYSLER EFC AND EFI
`SYSTEMS, 487
`
`Chapter 23
`TESTING A TYPICAL CHRYSLER EFC
`AND EFI SYSTEM, 511
`
`21·7
`
`ECM or PROM Replacement
`and Weather-pack Connector
`Service, 481
`Chapter Review, 485
`
`22·1
`
`22-2
`
`22·3
`
`EFC System Input Sensors
`and Switches- Temperature
`Compensation, 488
`EFC Output Command
`Signals, 491
`EFC Microcomputer and
`System Operation, 496
`Single-point EFI System
`Inputs, 498
`Single-point EFI System
`Output Devices, 501
`Single-point EFI Modules
`and System Operation, 504
`22-7 Multipoint EFI System, 507
`Chapter Review, 508
`
`22·4
`
`22-5
`
`22-6
`
`23-1
`
`23-2
`
`23-3
`23·4
`
`23·5
`
`23·6
`
`23·7
`
`Driveability Test
`Procedures Defined, 512
`Tools and Test Equipment
`Needed to Perform
`Diagnostic Tests, 513
`Test Categories, 516
`Visual and Operational
`Checks, 516
`Procedures for A No-start
`Condition, 518
`Driveability Test
`Procedures, 520
`Testing EFC Systems Without
`Self-diagnostic
`Capability, 522
`Chapter Review, 523
`
`Review Question and Answer Key, 525
`Index, 529
`
`

`

`Chapter4
`
`AUTOMOTIVE
`MICROCOMPUTERS
`
`OBJECTIVES
`
`After reading and studying this chapter, you will be
`able to
`
`• describe the function and basic design of a
`microcomputer.
`
`• explain the difference between analog and
`digital input signals.
`
`• describe the design and operation of a po(cid:173)
`tentiometer,
`t hermistor,
`and voltage(cid:173)
`generating input sensors.
`
`• explain how analog signals are converted to
`digital.
`• describe
`memory.
`
`types of computer
`
`the
`
`three
`
`• explain t he function and design of computer
`output devices.
`
`• describe how a microcomputer controls
`both open and closed loop engine operation.
`
`55
`
`

`

`56
`
`AUTOMOTIVE MICROCOMPUTERS
`
`T YPICAL COMPUTER OF THE
`1950'S
`
`HAND-HELD
`CALCULATOR
`
`FIGURE 4 - 1
`Early computer and a microcomputer within a calculator.
`(Courtesy of Ford Motor Co.)
`
`Ever since the first electronic calculators were
`built in the 1940s, the computer has proven itself to
`be an extremely flexible and reliable tool. With the
`advances in computer technology over the last 20
`years, this tool has been used to perform an increas(cid:173)
`ing number of tasks, including many on the automo(cid:173)
`bile.
`
`The first units were so large that one computer
`filled an entire room. These computers used vacuum
`tubes to control the flow of electrical signals. More(cid:173)
`over, a single computer contained thousands of
`these tubes. Consequently, these systems produced
`large amounts of heat and were prone to breaking
`down.
`
`As mentioned in the last chapter, today it is
`possible to produce miniature electronic circuits
`with the same amount of computing power. These
`miniature devices are called microcomputers. While
`large computers are used in business, industry, gov(cid:173)
`ernment research centers, and university laborator(cid:173)
`ies, microcomputers are now a component part of
`microwave ovens, hand-held calculators, wrist
`watches, and automotive engine control systems.
`A common hand-held calculator now has the
`same computing power as a large computer of the
`1950s (Fig. 4-1). However, the microcomputer in the
`calculator multiplies five times faster, adds ten
`times quicker, uses Yioo,ooo the amount of power, and
`requires Y16,ooo as much space as this full-size unit.
`
`4-1 MICROCOMPUTERS
`
`A microcomputer is an electronic device that con(cid:173)
`trols other electrical or mechanical units either to
`perform work or provide information. A microcom(cid:173)
`puter performs work by controlling the operation of
`such automotive components as solenoids and re(cid:173)
`lays. The unit provides information by controlling
`a display such as an electronic speedometer or fuel
`gauge. In any case, the microcomputer performs
`these functions by receiving, processing, and send(cid:173)
`ing out electrical voltage signals.
`The microcomputer is often referred to as the
`brains of an electronic engine control system. In this
`situation, the device receives information on vehicle
`operation and then decides how and when vehicle
`performance should be changed. Of course, a micro·
`computer does not think any more than a solenoid
`or relay. The microcomputer just passes small elec(cid:173)
`trical voltage signals from one circuit to another.
`However, these signals pass through the micro(cid:173)
`computer circuitry at an extremely rapid rate and in
`a predictable and logical manner. In fact, the typical
`unit is capable of receiving information, making a
`decision, and acting on it in less than one-tenth of a
`second. Because of this, the microcomputer is capa(cid:173)
`ble of controlling electrical and mechanical devices
`with great precision.
`
`Computers, Microcomputers, Processors,
`and Microprocessors
`
`When dealing with computerized engine control sys(cid:173)
`tems, a number of terms have become part of the
`language, including computer, microcomputer, proc-
`
`

`

`· COMPUTER
`
`AUTOMOTIVE MICROCOMPUTERS
`
`57
`
`-/
`__ _,.-::::...--
`
`/
`
`MEMORY
`
`' ' ' ' \
`
`\
`\
`\
`\
`I
`
`---·-
`I
`I
`.Im~~r- --- ---t------
`.... '---....
`- -
`- -
`I
`.--\
`----J. --~-
`- --.
`
`PROCESSOR
`
`FIGURE 4-2
`Differences in a computer. processor. microcomputer, and microprocessor.
`(Courtesy of Ford Motor Co.1
`
`II
`I
`
`I
`/ /
`
`/
`
`\
`\ '- MICRO-PROCESSOR
`'
`'
`
`/
`
`'---c~
`
`MICROCOMPUTER
`
`essor, and microprocessor. Unfortunately, even ex(cid:173)
`perts have a difficult time agreeing on just what
`these terms mean. In other words, a computer to one
`person is a microcomputer to another. Hopefully, t he
`definitions in this section will clear up the meaning
`of these terms.
`A computer is a large assembly of electronic
`components (Fig. 4- 2). A computer is not portable,
`and it is used to handle vast amounts of information
`or to control large operations. On an automotive as(cid:173)
`sembly line, for example, computers are used to con(cid:173)
`trol robotic assembly equipment.
`A microcomputer, on the other hand, is much
`smaller. In addition, the unit is portable and can eas(cid:173)
`ily fit into an automobile. Normally, the automobile
`microcomputer is built into a small box known as
`the processor. When the lid is taken off the proces(cid:173)
`sor, you can see a number of electronic parts inside
`it that make up the microcomputer.
`The microprocessor is the heart of the micro(cid:173)
`computer. This unit performs the calculations and
`
`controls microcomputer operation.
`Automotive processors, as used with engine
`control systems, are also called a number of other
`names by various manufacturers, including elec(cid:173)
`tronic control unit (ECU), electronic control module
`(ECM), electronic control assembly (ECA), and
`spark control computer (SCC).
`
`Microcomputer Types
`
`A microcomputer may be either analog or digital.
`An analog microcomputer operates on signals of
`varying voltage levels. The digital microcomputer
`requires voltage signals with a constant value.
`The digital microcomputer is generally consid(cid:173)
`ered to be more accurate. Therefore, almost all elec(cid:173)
`tronic engine control microcomputers are of the digi(cid:173)
`tal type. A few notable exceptions are the early
`Cadillac electronic fuel injected processor and the
`early Chrysler spark control computer.
`
`

`

`58
`
`AUTOMOTIVE MICROCOMPUTERS
`
`System diagram
`
`Analog Signals
`
`ECU
`
`IN P U T
`
`SHIFT INDICATOR LAMP
`¥ ~--4m~---+~~
`p
`¥
`
`TRANSMISSION SWITCH
`(ON AT 4TH-SPEED)
`~
`~
`BATIERY
`-1 ~. 4•>-------,J,.
`
`,-<=r---
`
`IGNITION COIL
`
`VEHICLE SPEED SENSOR
`
`~ WATER TEMPERATURE SENSOR
`
`THROTILE POSITION SENSOR
`
`An analog signal is one that varies continuously.
`This mean s that the signal can be any voltage within
`a given range. In other words, at any point in time,
`the voltage value of the analog signal may be high,
`low, or any value in between. In an engine control
`system, t he analog signal provides information to
`the microcomputer about an operating condition
`that is constantly changing over a certain range.
`Figure 4-4 illustrates an example of an analog
`signal. The signal begins at 0 volts and then in(cid:173)
`creases toward + 5 volts. After reaching a maximum
`of + 5 volts, the signal begins to decrease until it
`drops to 0 volts again. By graphing the change in
`voltage, a DC analog waveform is created.
`Most automotive sensors produce a DC analog
`waveform. The only exception to this is a magnetic
`sensor such as a distributor pickup coil. It produces
`an AC analog waveform (Fig. 4-5). In this situation,
`voltage is induced in the pickup coil first toward the
`positive and then toward the negative end, as
`shown.
`
`TO CARBURETOR
`...._ ____ ....,.!.._ VACUUM SWITCH
`
`Digital Signals
`
`FIGURE 4-3
`A number of sensors and switches provide input signals to
`the microcomputer. (Courtesy of Chrysler Motors Corp.)
`
`4-2 MICROCOMPUTER INPUT SIGNALS
`
`In order for the engine control microcomputer to
`perform its function, it has to receive a number of
`input signals from sensors and switches (Fig. 4-31.
`These signals provide information that the micro·
`computer will use in its decision-making process.
`The signals can be either analog or digital, both of
`which have distinct characteristics.
`
`A digital signal is one that has only two values. That
`is, the voltage is either on or off (Fig. 4-6). The
`graph in the illustration shows how the voltage val(cid:173)
`ues change as the switch is operated. The graph be(cid:173)
`gins with the signal off, which indicates the voltage
`is at 0 volts.
`When the switch turns the signal on, the graph
`shows the voltage value increase to 5 volts. But note
`that the change from 0 volts to 5 volts is very
`abrupt. Thrning the switch off again causes an
`abrupt drop in voltage from 5 volts to 0 volts.
`Thus, by graphing the changes in voltage, the
`DC digital waveform is created. Because of the
`abrupt changes in voltage, the final waveform has
`sharp corners and looks like a square. For this rea-
`
`NO
`VOLTAGE
`
`VOLTAGE
`INCREASING
`
`FULL VOLTAGE
`
`VOLTAGE
`DECREASING
`
`NO
`VOLTAGE
`
`5
`VOLTS
`
`0
`VOLTS
`
`'"<~' [\j
`VOLTS~
`
`FIGURE 4 -4
`DC analog signal. (Courtesy of Ford Motor Co.)
`
`

`

`AC ANALOG SIGNAL
`
`FIGURE 4-5
`AC analog signal.
`
`son. this type of waveform is also called a square
`wave.
`By turning a switch eiLher on or off rapidly, the
`waveform of the signal produced begins to look like
`the one illustrated in Fig. 4-7. Notice that the
`switch is off for slightly over the first second, on for
`part of t he second, and off a portion of the third. But
`during the fourth and fifth seconds, the switch re(cid:173)
`mains on; and for the sixth and seventh seconds, the
`switch is turned off.
`The only engine sensor that can by itself pro·
`duce a digital signal is one that uses a H all-effect
`switch, such as Ford's profile ignition pickup (PIP).
`However. microcomputer integrated circuitry actu(cid:173)
`ally consists of thousands of tiny switches. As these
`are turned on and off, they can produce waveforms
`that are s imilar to the one shown in Fig. 4- 7.
`
`Binary Code
`
`Because a digital signal varies between two values,
`t he state of the signal can be described as being
`either on or off, or t he voltage can be described as
`either high or low. Moreover, digital signals can be
`assigned a numeric value. For example. a signal that
`is on can be represented by l (one) and an off signal
`by 0 (zero).
`
`AUTOMOTIVE MICROCOMPUTERS
`
`59
`
`HIGH
`VOLTAGE-
`
`LOW -p..-0-FF_.
`VOLTAGE
`
`0
`
`ON
`
`ON
`
`OFF -
`
`4
`3
`2
`nilE (IN SECONDS)
`
`Of'f' OFF
`
`II
`
`•
`
`FIGURE 4 - 7
`Typical digital waveform. (Courtesy o f Ford Motor Co.)
`
`BINARY
`CODE
`
`0
`
`0
`
`0
`
`HIGH
`VOLTAGE
`
`LOW
`VOLTAGE
`
`2
`
`nMI! (!N SECONDS)
`
`•
`
`FIGURE 4-8
`Binary code. (Courtesy of Ford M otor Co.)
`
`This system of assigning a numeric value to
`voltage signals is known as binary coding (Fig. 4-8).
`The word binary means two values. The two values
`in the binary code system are l and 0.
`F urthermore, each 0 and each l is known as a
`BIT of information from t he term binary digit.
`Eight bits together are known as a BYTE, which
`forms a word in computer language. A word, there(cid:173)
`fore, contains any combination of eight binary code
`bits: eight l s, or five l s and three Os, or two ls and
`six Os, and so on.
`Binary code is used inside a microcomputer
`and between it and any electronic device that under-
`
`SWITCH
`TURNED ON
`
`svo•~ Ji """"®
`
`SWITCH
`TURNED OFF
`
`SVOLTS
`
`OVOLTS
`
`SVOLTSL
`
`0 VOLTS
`
`SIGNAL OFF
`
`OVOLTS
`
`FIGURE 4 - 6
`DC digital signal. (Courtesy o f Ford Motor Co.)
`
`

`

`60
`
`AUTOMOTIVE MICROCOMPUTERS
`
`stands binary code. Letters, numbers, and condi(cid:173)
`tions are then represented in this binary code by a
`given series of ls and Os, and then transmitted as
`such. By stringing together thousands of bits, mi(cid:173)
`crocomputers can communicate and store an infinite
`variety of information. Therefore, any data that can
`be represented in binary code can be processed by
`the microcomputer.
`Since the microcomputer is very good at work(cid:173)
`ing with numbers, it is able to perform calculations
`at an extremely rapid rate. Information is transmit(cid:173)
`ted in binary code by switching voltage on and off
`at a very rapid rate (i.e., thousands of times per
`second).
`
`4-3 MICROCOMPUTER INPUT
`SIGNAL SOURCES
`
`As mentioned, in order for a microcomputer to per(cid:173)
`form its function, it must have input information.
`Sensors in an engine control system provide this in(cid:173)
`put. Automotive engine sensors are typed by the
`manner in which they relay input signals to the mi(cid:173)
`crocomputer. The most common types of sensors are
`the potentiometer, switch, t hermistor, detonation,
`and voltage-generating.
`
`Reference Voltage
`
`Before discussing sensors, it is important to under(cid:173)
`stand what reference voltage is and how it is pro(cid:173)
`duced. Reference voltage is a constant voltage that
`is supplied by the microcomputer to some of the sen(cid:173)
`sors. These sensors must have this reference voltage
`in order to produce an input signal. The sensor types
`that use reference voltage are the potentiometer,
`switch, and thermistor.
`A voltage regulator inside the microcomputer
`supplies the reference voltage (VREF) of between 5
`volts and 9 volts to these sensors (Fig. 4-9). The sen(cid:173)
`sors, in turn, change the voltage level in proportion
`to some factor relating to engine operation. The re(cid:173)
`sulting input signal is then relayed back to the mi(cid:173)
`crocomputer for processing.
`
`Potentiometer
`
`The potentiometer is a sensor that converts mechan(cid:173)
`ical motion to a voltage value. The potentiometer is
`used to signal the position of such components as
`the throttle and exhaust gas recirculation (EGR)
`
`valves or the movement of a diaphragm operated by
`atmospheric pressure or a vacuum.
`'!ypical potentiometer-type sensors in use in
`engine control systems are the throttle position sen(cid:173)
`sor (TPS), vane airflow sensor, and EGR valve posi(cid:173)
`tion sensor.
`The typical potentiometer-type TPS consists
`of a resistance material, wiper, and three connectors.
`Full reference voltage is supplied to the first connec(cid:173)
`tor, which is located on one end of the resistance ma(cid:173)
`terial. The second connector provides a signal return
`(ground) for the resistor through the processor. The
`third signal voltage connector is located on the end
`of the wiper arm (see Fig. 4-9). The tip of the wiper
`contacts t he resistor material.
`As t he wiper arm moves along the resistance
`material in response to changes in throttle valve
`angle, the voltage at the signal connector will in(cid:173)
`crease or decrease. For instance, with the throttle
`plate fully open (i.e., at 80 to 85 degrees) the voltage
`signal to the processor is nearly 5 volts, or reference
`voltage (Fig. 4- 10). However, as the throttle plate
`closes (angle decreases), the signal voltage drops un(cid:173)
`til it reaches about 0.5 volt at closed throttle (i.e., a
`0 degree angle).
`In the t hrottle position sensor and in the other
`potentiometer-type units, the signal voltage in(cid:173)
`creases or decreases by changing the resistance be·
`tween the reference voltage connector and the wiper
`arm connector. With the throttle plate fully open, for
`example, the wiper assumes a position on the resis(cid:173)
`tor t hat produces t he least amount of resistance be(cid:173)
`tween the two connectors. At closed throttle, on the
`other hand, there is maximum resistance between
`the two connectors. The total resistance then
`changes between the two points as the wiper moves
`along the resistor.
`
`Switches
`
`A switch is also frequently used to signal the micro(cid:173)
`computer, indicating the position of a component.
`However, in this case the signal voltage has only two
`values, high and zero, indicating that the switch is
`either closed or open.
`'!ypical examples of switches used for t his pur(cid:173)
`pose include the neutral safety switch, the brake on/
`off switch, the clutch engaged switch, the key-on
`switch, and the air conditioning clutch switch.
`Figure 4- 11 illustrates a typical circuit of a
`switch-type sensor, a clutch engaged switch (CES).
`In this installation, an electrically conductive blade
`moves between two contacts. When the switch is
`
`

`

`REFERENCE VOLTAGE OF 5 VOLTS (VREF)
`FROM
`REGULATOR
`
`mrnrn
`
`OUTPUT
`DRIVERS
`
`5 VREF
`
`THROTTLE PLATE
`FULLY OPEN
`
`SIGNAL RETURN
`PROVIDED
`THROUGH
`MICROCOMPUTER
`
`VOLTAGE
`AL
`
`THROTTLE PLATE SIGNAL
`PAfHIALL y
`RETURN
`CLOSED
`
`THROTT\.E .PLATE
`CLOSED
`
`SIGNAL
`RETURN
`
`FIGURE 4- 9
`Schematic of the reference voltage source and a throttle po(cid:173)
`sition sensor. (Courtesy of Ford Motor Co.)
`
`61
`
`

`

`62
`
`AUTOMOTIVE MICROCOMPUTERS
`
`5.0
`
`4.0
`
`w
`<:J
`<{
`~ 3.0
`0
`>
`1--
`:= 2.0
`:J
`
`:J
`0
`
`1.0
`
`0.5
`
`0
`
`10
`
`70
`60
`50
`40
`30
`20
`THROTILE ANGLE (DEGR EES)
`
`80 85
`
`FIGURE 4-10
`TPS voltage curve.
`
`closed, the blade touches both contacts and current
`flows through the switch. In this case, the signal
`voltage to the microcomputer will be less than one
`volt because current flows through the switch to
`ground at the processor.
`When the clutch pedal is released, the CES
`switch opens, as shown in Fig. 4-11. In this case,
`current cannot flow through the switch to the proc(cid:173)
`essor ground. Consequently, current flows through
`the signal voltage connector at a potential of nearly
`five volts.
`
`Thermistors
`
`A thermistor-type sensor is a device that converts
`temperature into a voltage signal. That is, the unit
`develops a voltage signal in proportion to changes
`in temperature. A t hermistor device is made of a
`semiconductor material, the resistance of which var(cid:173)
`ies as its temperature increases or decreases. In
`other words, the thermistor is a form of variable re(cid:173)
`sistor. As shown by the curve in Fig. 4-12, t he re(cid:173)
`sistance of the thermistor decreases as its temper(cid:173)
`ature goes up. Conversely, its resistance increases as
`t he temperature decreases.
`A thermistor-type sensor is therefore used to
`measure such things as engine coolant, air cleaner,
`intake manifold, or passenger compartment temper(cid:173)
`atures. 'JYpical thermistor-type sensors are used in
`computerized engine control systems to measure en(cid:173)
`gine coolant temperature, charge temperature, and
`vane air temperature.
`Figure 4-13 is a schematic of an engine coolant
`temperature (ECT) sensor circuit. Notice t he ECT is
`represented on the diagram by the variable resistor
`symbol. Moreover, like any type of thermistor, the
`ECT has two connections. The top connection pro(cid:173)
`vides the reference voltage from t he processor; a
`ground circuit is provided through t he processor via
`the lower connector.
`A special signal line branches off the reference
`voltage line to provide the ECT input signal back
`to the processor. As the resistance of the thermistor
`
`HIGH VOLTAGE SIGNAL
`(SVOLTS) TO
`INPUT CONDITIONERS
`
`CURRENT LIMITING
`RESISTOR
`
`CLUTCH
`PEDAL
`RELEASED
`
`SIGNAL RETURN PROVIDED
`THROUGH PROCESSOR
`
`FIGURE 4-1 t
`Typical switch schematic. (Courtesy of Ford Motor Co.)
`
`

`

`increases or decreases, this input signal changes.
`The microcomputer t hen uses t his voltage signal to
`determine changes in engine temperature.
`When the engine is cold, the resistance of t he
`ECT sensor is high (see Fig. 4-13). As a result, a
`high voltage input signal is routed back to t he proc(cid:173)
`essor. But as engine temperature increases, the re(cid:173)
`sistance of the ECT sensor decreases, and more cur·
`rent flows t hrough t he sensor to groun d. This action
`decreases the ECT input signal to t he processor
`(Fig. 4-1 4).
`
`AUTOMOTIVE MICROCOMPUTERS
`
`63
`
`HIGH I
`
`RESISTANCE
`
`LOW
`
`LOW- - - - TEMPERATURE - - - - HIGH
`
`FIGU RE 4 -12
`Thermistor temperature versus resistance curve.
`
`CURRENT LIMITING
`RESISTOR
`
`HIGH VOLTAGE
`SIGNAL IS
`RELAYED
`TO INPUT
`CONDITIONERS
`
`COLO
`ENGINE
`
`FIGURE 4-13
`Typical engine coolant temperature (ECT) circuit with the
`engine cold. (Courtesy of Ford Motor Co.)
`
`5VREF
`
`CURRENT LIMITING
`RESISTOR
`
`LOW VOLTAGE
`SIGNAL IS
`RELAYED TO
`INPUT
`CONDITfONERS
`BECAUSE ••.
`
`.. . ECT
`RESISTANCE
`IS LOW
`
`HOT
`ENGINE
`
`FIGURE 4- 14
`Typical ECT circuit w ith the engine hot. (Courtesy of Ford
`Motor Co.)
`
`

`

`64
`
`AUTOMOTIVE MICROCOMPUTERS
`
`PRESSURE APPLIED
`TO CRYSTAL •..
`
`ELECTRICAL
`VOLTAGE
`
`FIGURE 4- 15
`Design and operation of a piezo-electric sensor. (Courtesy
`of Ford Motor Co.)
`
`Voltage-Generating Sensors
`
`A voltage-generating sensor is not supplied with a
`reference voltage. Instead, the sensor generates its
`own signal for use by the processor. This type of sen(cid:173)
`sor uses a variety of means to create the input volt(cid:173)
`age signal. In some of these sensors, a certain type
`of quartz crystal is used to generate voltage. Others
`utilize electrically conductive materials or electro(cid:173)
`magnetic principles to generate the voltage.
`
`The types of devices t hat are voltage generat(cid:173)
`ing include t he detonation sensor, exhaust gas oxy(cid:173)
`gen sensor, distributor magnetic pickup sensor, and
`Hall-effect switch.
`
`Detonation Sensors
`
`A detonation sensor is a piezo-electric device that
`converts vibration or motion into an electrical volt(cid:173)
`age. This type of sensor is commonly used to moni(cid:173)
`tor t he vibrations resulting from engine detonation,
`or spark knock.
`A typical piezo-electric sensor consists of a spe(cid:173)
`cial quartz crystal sandwiched between two electri(cid:173)
`cally conductive electrodes (Fig. 4-15). As pressure
`is applied to the crystal, a voltage is generated be(cid:173)
`tween the two electrodes.
`Figure 4-16 illustrates this device as it appears
`in a schematic of a detonation or knock sensor. The
`knock sensor threads into the engine block or intake
`manifold where it can detect engine vibrations. (The
`engine block or intake manifold also forms the sen(cid:173)
`sor ground return circuit.) The voltage signals pro(cid:173)
`duced by the sensor as a result of these vibrations
`are then relayed back to the processor in the form of
`voltage signals.
`The typical engine produces many kinds of vi(cid:173)
`brations during normal engine operation. For t his
`
`KNOCK SENSOR $1GNAL
`IS RELAYED TO
`INPUT CONDITIONERS
`
`SIGNAL RETURN PROVIDED
`THROUGH PROCESSOR-
`
`PRODUCES
`ENGINE
`VI BRATtON
`
`FIGURE 4-16
`Typical detonation sensor circuit. (Courtesy of Ford Motor Co.)
`
`

`

`PROTECTING
`SHIELD
`
`ZIRCONIUM
`DIOXIDE BODY
`
`SHELL
`
`INTERNAL AND
`EXTERNAL SURFACES
`PLATINUM PLATED
`
`WIRE
`TO ELECTRONIC
`FUEL CONTROL
`COMPUTER
`
`FIGURE 4-17
`Typical oxygen sensor. [Courtesy of Chrysler Motors Corp.)
`
`reason, a knock sensor is tuned to respond only to
`the type of vibrations produced by detonation.
`In operation, the vibrations are transmitted
`via the engine block or intake manifold to the knock
`sensor where they place pressure on the quartz crys(cid:173)
`tal inside the sensor. This results in a voltage signal
`that is passed back to the processor as input. The
`more severe the vibrations, the higher the voltage
`signal will be.
`
`Exhaust Gas Oxygen Sensor
`
`The exhaust gas oxygen sensor develops a voltage
`signal based on the amount of oxygen present in the
`exhaust gases (Fig. 4-17). The resulting input signal
`is used by the microcomputer to determine an en(cid:173)
`gine's air/fuel ratio.
`The exhaust gas oxygen sensor typically
`threads into the exhaust manifold that also forms
`the ground side of its circuit. The sensor detects the
`presence of oxygen in the exhaust gases and then
`produces a variable voltage, according to the
`amount that is present at any giv