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`System
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`L—';le'rronic
`DaJelronic “r-
`KE-Motronic
`KE-Jetronic -
`KéJetronic'
`“.3
`
`
`
`Robert Bentley,
`Publishers
`
`VW EX1016
`
`U S Patent No. 6,557,540
`
`VW EX1016
`U.S. Patent No. 6,557,540
`
`

`

`Published and Distributed by:
`
`Robert Bentley, Inc, Publishers
`1000 Massachusetts Avenue
`Cambridge. Massachusetts 02138
`
`.
`
`‘
`
`'
`
`l" 7
`
`‘5
`
`F (.5
`N J at
`
`Copies of this manual may be purchased from selected booksellers. automotive accessories and parts dealers, or directly from the
`publisher by mail.
`
`CAUTION
`
`
`. motive repair procedures. Before attempting any work on your car. read the
`_
`-
`. no. the publisher. and the author have made every effort to ensure the accuracy
`
`_r--"""
`cfthis manual. Neith r can be he i
`. 'nnsible torthe resultpt any error in this manual.
`_..- -
`
`NOTE To usens 0 ;THIS mew—{d I
`
`The publisher encourages comments from the readers of this manual. These communications have been and will be carefully
`considered in the preparation of this and other manuals. Please write to Floberl Bentley. Inc. Publishers, at the address on this page.
`
`This manual was published by Robert Bentley. inc, which has sole responsibility for its content. Flobert Bosch Corporation has not
`reviewed and does not vouch for the accuracy of the technical information and procedures described in this manual.
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`The author and publisher would like to thank and acknowledge Robert Bosch Corporation for the permission to use and reproduce
`a great many of their technical illustrations and photographs.
`
`Since this page cannot legibly accommodate all the copyright notices. the art credits pages at the back of the book listing the source
`of the illustrations and photographs used, constitute an extension of the copyright page.
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`Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those
`designations appear in this book and Robert Bentley. inc. was aware of a trademark claim. the designations have been printed in
`initial capital letters (e.g.. Jetronic).
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`Library of Congress Catalog Card No. 39-61946
`lSBN 0-8376—0300-5
`Bentley Stock No. GFIB
`
`3591908910987654321
`Library Materials
`'
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`© 1989 Robert Bentley. inc.
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`meets the requirements at American National Standard for Inlormation Sciencas- Permanence or Paper for Pril'lifl'cl
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`all rights reserved. All information contained in this book is based on information available at the time of first printing. The right
`is reserved to make changes at any time without any notice. No part of this publication may be reproduced, stored in a retrieval
`system. or transmitted to any form or by any means. electronic. mechanical. photocopying, recording. or otherwise. without the
`prior written permission of the publisher. This includes text. figures and tables. This book is published simultaneously in
`Canada. All rights reserved under Bern and PanrArn
`‘
`
`Front cover: Bosch LH-Jetronic Air-mass sensor hot wire
`air-mass sensors. see chapter 3. Courtesy Boson.
`
`of Dr. Ing. h.c.F. Porsche AG. Volvo 740 GL Wagon in SCCA Escort Endurance
`Courtesy Volvo Cars of North America. Volkswagen Golt GL. Courtesy Volkswagen United States, inc.
`Sole United Kingdom distribution by
`Motor Racing Publications Limited
`Unit B. The Filton Estate
`46 Pitiake. Croydon CRO 3Fl‘l'. England
`
`

`

`.
`-
`.....v—u
`W ___.—w——w———_m __, -,
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`
`'
`
`...1.
`
`Contents:
`
`Bosch Fuel Injection
`
`
`Bosch Fuel Injection—An Overview 3
`
`Engine Management Fundamentals ,.
`
`Pulsed Injection—Theory
`
`'-
`
`Pulsed Injection——Troub|eshooting & Service
`
`Continuous Injection—Theory
`
`
`
`Continuous Injection—Troubleshooting & Service
`
`Tuning for Performance and Economy
`
`Appendix
`
`Glossary Index
`
`323-16EC;
`
`

`

`This material may be protected by Copyright law (Title 17 U.S. Code)
`
`

`

`
`

`

`ENGINE MANAGEMENT FUNDAMENTALS
`
`3
`
`1 .
`
`INTRODUCTION
`
`What sets fuel—injection and enginemanagement systems
`apart from otherfuel delivery systems is their ability to precisely
`control fuel metering and adjust it
`in reSponse to changing
`operating conditions. The key elements in the success of
`Bosch fuel-injection and engine-management systems are (a)
`a comprehensive understanding of the engine‘s varying fuel
`delivery requirements over a broad range of operating condi-
`tions. (b) extensive research into how the factors which influ-
`ence the engine's fuel needs can be measured and interpreted
`by control systems and.
`(c) highly developed methods for
`
`controlling fuel metering to optimize overall performance. .i-LJ;.‘-i:‘-'.'é.fl-‘:ri:
`
`In this chapter. I'll review the basic factors governing air-fuel
`mixture and fuel delivery.
`I'll describe why various engine
`operating conditions demand different air-fuel mixtures, and I'll
`explain how the air-fuel ratio can be manipulated to improve
`driveability and control exhaust emissions with little sacrifice of
`power. In chapter 3 and chapter 5, you’ll see how Bosch
`applies these principles to the design and operation of their
`fuel-injection systems.
`
`2. BASIC FACTORS
`
`First. the basics. We‘ll take a closer look at air-fuel ratios and
`the engine's basic demands for a combustible mixture.
`I‘ll
`describe additional factors affecting fuel delivery which are
`imposed by the demands of the car-buying public, and we‘ll
`examine pressure and pressure measurement—a subject that
`is fundamental to understanding how Bosch fuel—injection sys-
`tems work.
`
`2.1 Air-Fuel Hatios
`
`An engine's throttle controls the amount of air the engine
`takes in. The main function of any fuel delivery system is to mix
`fuel with that incoming air in the proper ratio. Small variations in
`air-fuel ratio can have dramatic effects on power output. fuel
`consumption. and exhaust emissions.
`
`The Basic Combustible Mixture
`
`Laws of physics tell us that combustion of any substance
`requires a sufficient ratio of surface area to mass (small enough
`particles). and the correct amount of oxygen fin proportion to
`the amount of fuel).
`in Internal combustion engines these
`conditions are met by atomizing the fuel into tiny droplets. and
`by metering fuel in correct proportion to the intake air. In round
`numbers, approximately 14 parts of air are required to support
`complete combustion of 1 part of fuel Ain other words. an
`air-fuel ratio of about 14:1.
`
`Flg. 2_1_ Bymass. it takes about 14 parts of air to support
`complete combustion of 1 part of fueL Before it;
`day's concerns over fuel economy and emissions.
`an air-fuel ratio somewhere close to 14:1 was good
`enough-
`
`
`
`
`
`11.5{JIDI
`
`practice and discussairfuel ratiosor
`let
`hsisth srri festandbestwa t
`e!
`o
`mass“
`P 1 P
`1.199 risk 9
`
`
`
`Basic Factors
`
`

`

`4
`
`ENGINE MANAGEMENT FUNDAMENTALS
`
`Notice that I am talking about combustion that is complete -
`combustion that makes the best. most thorough use of fuel.
`Air-fuel ratios which are higher or lower than approximately
`14:1 will still burn. but such combustion produces unwanted
`by-products and other side effects. As you read further into this
`chapter. you'll see what those are. and why precise control of
`the air-fuel ratio has become so important.
`
`Rich and Lean Mixtures
`
`The terms "rich“ and "lean" are used to describe mixtures
`which deviate from the theoretically perfect air-fuel ratio and
`burn less efficiency.
`
`A rich mixture is one with a lower airtuel ra’a’o: there is
`insufficient air (oxygen) to support complete combustion oi the
`luel. Ftich mixtures increase fuel consumption and emissions oi
`hydrocarbons (HC) and carbon monoxide (cm—me products
`of incompletely bumed gasoline. They tend to reduce power,
`increase carbon deposits and. in the extreme case, foul spark
`plugs and dilute the engine’s lubricating oil.
`
`“Enrichment” is the process of metering more fuel for a
`given amount of air to produce a richer mixture.
`
`
`
`Fig. 2-3. Rich mbriures contain more fuel than can be com
`pletely burned in the given amount of air.
`
`A lean mixture is one with a higher air-fuel ratio: there is
`more air than necessary for complete combustion of the toel.
`The fuel will bum completely. but more slowly and at a higher
`combustion temperature. Lean mixtures reduce power. elevate
`engine temperature, and increase emissions or oxides of nitro-
`gen [N03 —a product of combustion at excessively high tem-
`perature. They also tend to cause driveability problems. In the
`extreme case, the high temperatures resulting from lean com-
`bustion will cause preignition— violent. untimed combustion of
`the mixture which has the potential to cause serious engine
`damage.
`
`Basic Factors
`
`
`
`Fig. 2-4.. Lean mixtures contain more air than is necessary
`for combustion of the fuel. Inferior combustion re-
`duces power and can cause engine damage
`
`Stoichicmetrlc Flatio
`
`When "935 was cheap and the air was dirty." carburetors
`were usually set up to deliver mixtures richer than 14:1. per-
`haps with an air-fuel ratio as low as 12:1. As the car aged and
`a little excess air leaked in around the gaskets otthe carburetor
`or the intake manifold. the engine still got a good combustible
`mixture. Then, too. the carburetor was tarther from the and
`cylinders than from the middle ones. A richer mixture was some
`compensation for unequal fuel distribution.
`
`There was another reason for setting up carbureted engines
`to run a iittte rich. Air-fuel mixture was less precise. and some
`variations were to be expected. As shown in Fig. 2-5, variations
`in a rich mixture have only a small ettect on power. while
`variations in a lean mixture affect power dramatically.
`Rich air-fuel variation
`'— I
`
`Same variation
`lean air—fuel
`
`e221r=uxacH
`
`Rich 4— Air-l'uelratlo -—- Lean
`
`Fig. 2-5. Variation in a rich air-fuel ratio makes much less
`difference in powar than the same variation in a lean
`air-iuel ratio.
`
`

`

`ENGINE MANAGEMENT FUNDAMENTALS
`
`5
`
`While power is always a requirement. modem fuel delivery
`systems face additional demands. increasing concern over the
`cost and availability 01 gasoline has resulted in greater demand
`for fuel economy. Environmental concerns and resulting legis-
`lation demand rigid control of harmful exhaust emissions And,
`the
`car-buying
`public
`increasingly
`demands
`good
`driveability—quick-starb'ng and smooth.
`trouble-free perfor-
`mance under any and all operating conditions. Each of these
`factors places different demands on the fuel delivery system,
`and there are trade—offs.
`
`Adjusting the system tor maximum power also means in-
`creasing fuel consumption. Minimizing tuel consumption
`means sacrificing power and driveability. Choosing either max-
`imum power or minimum fuel consumption means increased
`exhaust emissions The modern fuel delivery system must be
`able to maintain strict control of air-fuel ratio in order to achieve
`the best compromise and meet these conflicting demands in
`the most acceptable way. in general. this means slight sacri-
`fices of power and fuel economy in exchange for optimum
`emissions control.
`
`Stoichiometric
`(Ideal)
`
`
`
`For today’s engines, with the increased emphasis on fuel
`economy and reduced emissions. the air-fuel ratio has to be
`controlled much more carefully. The "ide " air-fuel ratio —the
`one which yields the most complete combustion and the best
`compromise between lean and rich mixtures— is 14.7:1. This is
`called the "stoichiometric” ratio. The mixture is neither rich nor
`lean.
`
`The Excess Air Factor—Lambda
`
`The stoichiometric ratio can also be described in terms of
`the air requirements ofthe engine. Bosch calls this the "excess
`air factor" and represents it using the Greek letter it (lambda).
`At the stoichiometric ratio—when the amount of air equals the
`amount required for complete combustion of the fuel and there
`is no excess air— lambda (it) = 1.
`
`
`
`Fig. 2-6. The ideal or "stoichiometrio" air—tuel ratio—When
`there is just enough air to burn all
`the fuel—is
`14.7:1. This is also described as it (Iambdal = 1.
`
`When there is excess air (air-fuel ratio leaner thanstoichio—
`metric). lambda is greater than one. When there is a shortage
`of air (air-fuel ratio richer than stoichiometrlc). lambda is less
`than one.
`
`The concept of lambda (the excess air factor) was created
`specifically to support thinking about fuel delivery in terms of
`the air requirements of the engine. As you'll see later on. this
`concept plays a big part in controlling exhaust emissions.
`
`2.2 Driveability and Emission Control
`
`l’ve described the engine’s basic requirement for a com-
`bustible mixture of air and fuel, how variations in mixture influ-
`ence performance. and how older carburetor systems tended
`to run richer than the ideal air-fuel ratio in the interest of
`
`delivering smooth. reliable power.
`
`Air-fuel ratio = 12.6;1
`Lambda it) 20.86
`
`\
`
`Fuel—/
`consumption
`
`‘5.
`
`"- 5.
`
`Best fuel
`economy
`
`Lambda (it) = 1
`
`|I
`
`I l
`
`,
`
`-- -O-' -- "'
`Air-fuel ratio = 154:!
`Lambda (it) =1 .05
`
`Air-fuel ratio 214.7:1
`
`Fig. 2-7. The airsfuel ratio which delivers maximum power is
`slightly richer than stoichiometric; the one which
`delivers minimum luel cchsumptibn is slightly more
`lean than stoichiometn‘c. The stoichiometric ratio is
`a compromise which sacrifices very little of either.
`
`Basic Factors
`
`

`

`6
`
`ENGINE MANAGEMENT FUNDAMENTALS
`
`control. In addition. government legislation established an av—
`erage mpg standard to apply to the total fleet of cars each
`manufacturer delivers each year. Further, the target mpg stan-
`dard rose each year, starting at 18 mpg in 1978. and rising to
`27.5 mpg in 1985, but cut back in 1966 to 26 mpg. Fuel
`injection's precise control of fuel delivery minimizes fuel con-
`sumption while still providing good driveability.
`
`2.3 Air Flow, Fuel Delivery, and Engine Load
`
`You know that air is drawn into the engine with each intake
`stroke of each piston. The piston moving down on its intake
`stroke increases cylinder volume and lowers pressure in the
`cylinder. With the intake valve open. air at higher pressure
`rushes in from the intake manifold to fill the cylinder. The
`amount of fuel necessary to create a stoichiometric mixture
`depends on how much air rushes in.
`
`in simplest terms. intake air flow occurs because normal
`atmospheric pressure is higher than the pressure in the cylin-
`ders. Air rushes in during the intake stroke. trying to equalize
`the pressure. In gasoline engines. the throttle valve restricts
`intake airflow. As you open the throttle. the opening to atmo—
`spheric pressure raises manifold pressure. So, in practice. the
`amount of air that rushes into the cylinder on the intake stroke
`depends on the difference between the pressure in the intake
`manifold and the lower pressure in the cylinder. Pressure in the
`intake manifold depends on throttle opening.
`
`The greatest intake air flow occurs when the throttle valve is
`fully open. The throttle valve causes almost no restriction, and
`full atmospheric pressure is admitted to the intake manifold.
`This creates the greatest possible difference between manifold
`pressure and cylinder pressure. and the greatest intake airflow.
`
`Atmospheric
`pressure
`
`Open throttle
`piste
`
`High Intake
`anilold pressure
`
`Intake valve
`
`Intake stroke
`
`Fig. 2-9. At full throttle. nearly unrestricted atmospheric pres—
`sure raises manifold pressure. Large pressure dif-
`ferential between manifold and cylinders increases
`airflow.
`
`Excess-air iactor it
`
`U)E
`_oa
`11
`
`EE{
`
`mw2
`
`3‘
`‘d-i3(O
`E
`
`Fig. 2-5. Stoichicmetric air—fuel ratio [it = 1) yields the best
`compromise for control of hydrocarbon (HG). car-
`bon monoxide (CO). and oxides of nitrogen (N03
`emissions, belore the catalytic converter (a) or after
`it (b).
`
`It is fuel injection's ability to maintain the air-fuel ratio within
`close tolerances that makes it superior to carburetor systems.
`For the manuiacturer, fuel-injection means better emission
`concol and better fuel economy, both important in meeting
`increasingly stringent government regulation. For the owner.
`lust-injection means achieving fuel economy and emission
`control while preserving driveability and maximum power.
`
`Fuel Economy - CAFE
`
`Along with the general demand for fuel economy. each
`manufacturer must consider another factor: mandated federal
`standards for rated fuel economy —the Corporate Average Fuel
`Economy (CAFE) standards. The industry trend in rated miles-
`per-gallon (mpg) turned upward beginning in 1975. as catalytic
`converters replaced engine de-tuning as a means of emission
`
`Basic Factors
`
`

`

`ENGINE MANAGEMENT FUNDAMENTALS
`
`7
`
`The least intake air flow occurs when the throttle is nearly
`closed. The restriction of the throttle valve limits the effect at
`atmospheric pressure. There is little difference between man-
`ifold pressure and the low pressure in the cylinders. and airflow
`is low.
`
`Atmospheric
`pressure
`
`Low intake
`manifold pressure
`
`plate
`
`Closed throttle
`
`Fig. 2-10. With the throttle closed. atmospheric pressure has
`little effect on manifold pressure. Low pressure
`differential between manifold and cylinders results
`in little air flow.
`
`Fuel delivery requirements depend more than anything else
`on how much work you are asking the engine to do—on how
`much of a “load" you are placing on it. To accelerate, you step
`down harder on the accelerator. This opens the throttle valve.
`increasing manifold pressure. The greater pressure difference
`between the manifold and the cylinders increases intake air
`flow. and therefore fuel flow. to increase power and accelerate
`the car.
`
`Driving down a level road. you can cmise along comfortably
`and maintain a desired speed with a relatively small throttle
`opening. When you come to a hill,
`it is necessary to press
`farther down on the accelerator to maintain the same speed.
`even though engine rpm is unchanged. The hill has demanded
`more work from the engine— created a higher load—and the
`engine has demanded more air and fuel to match that load.
`
`Regardless of engine speed. the air flow and fuel delivery
`demands ofthe engine depend on the load being placed upon
`it. That load, and the resulting throttle opening, directly affect
`manifold pressure. Manifold pressure in turn attests air flow and
`thus fuel requirements.
`
`2.4 Fuel Pressure
`
`Both carburetors and fuel-injection systems rely on pres
`sure or pressure differential to dispense fuel into the intake air
`Stream. The atomized fuel vaporizes and mixes with the air to
`Produce a combustible mixture.
`
`In a carburetor system. the fuel system supplies fuel to the
`carburetor float bowl. The bowl is vented. and the fuel in the
`bowl is at atmospheric pressure. Intake air passing through the
`carburetor's venturi creates low pressure in the venturi—lower
`than atmospheric pressure. This pressure differential —
`between atmospheric pressure in the carburetor bowl and
`reduced pressure in the venturi chamber—causes fuel to flow
`from the bowl through the discharge nozzle, and into the intake
`air stream.
`
`Atmospheric
`pressure: 14.5 psi
`
`
`
`BZEZFUNBCH
`
`Air pressure
`at Venturi:
`
`foresaw,,
`
`r ’3
`
`'Main
`metering
`jet
`
`Fig. 2-11. The fuel-metering part of a carburetor operates
`with small differences in pressure: fuel in the bowl
`at atmospheric pressure vs. reduced pressure at
`the discharge nozzle in the venturi.
`
`The pressure differential in the fuel-metering system of a
`carburetor is usually pretty small—only a few pounds-per-
`square-inch (psi). In contrast. fuel-injection systems introduce
`the fuel at higher pressures. anywhere from 30 to 90 psi
`depending on the system and specific operating conditions.
`Fuel delivery at these higher pressures ensures that the fuel is
`better atomized. and it is vaporized more completely in the
`airstream. Higher fuel pressure also makes possible more
`precise control of fuel delivery.
`
`2.5 Pressure Measurement
`
`As i get into the specific functional details of each of the
`various fuel—inlection systems. you’ll see that many functions
`and relationships are defined in terms of pressure. They may
`be fuel pressure values in the fuel system, manifold pressure in
`the air intake system, or atmospheric pressure. i may be talking
`about a differential pressure—the difference between two op-
`posing pressure values somewhere in the system.
`
`Basic Factors
`
`

`

`8
`
`ENGINE MANAGEMENT FUNDAMENTALS
`
`Gauge Pressure vs. Absolute Pressure vs.
`Vacuum
`
`I've described engine intake air flow and load in terms of
`manifold pressure, and I've discussed the units of measure
`used to describe pressure. Now it is important that you under-
`stand exactty what you are measuring.
`
`For many years, people have traditionally thought about
`engine air flow and load in terms of vacuum—the "vacuum”
`created in the intake manifold by the pistons' intake strokes.
`Using atmospheric pressure as a baseline. as zero. the lower
`manifold pressure is expressed as a negative value—vacuum.
`
`By the 19805, the automotive industry had moved away
`from thinking in terms of vacuum. Widespread use 01 fuel
`injection began to demand more accurate measurement of
`manifold “vacuum", and turbocharging —where manifold pres-
`sure may exceed atmospheric pressure—began to blur the
`distinction between vacuum and pressure. A simpler and more
`useful approach is to think in terms of manifold absolute pres-
`sure (MAP). MAP refers to the pressure in the intake manifold
`which is positive compared to zero absolute pressure. rather
`than negative compared to atmospheric pressure.
`
`If that seems hard to understand. think of atmospheric
`pressure at sea level. We tend to think of this as zero pressure
`and, in fact, an open fuel-pressure gauge will read 0 at sea
`level. But remember. atmospheric pressure at sea level
`is
`actually 1 bar (14.5 psi). Almost all pressure gauges use atmo-
`spheric pressure as their reference. Any measurement made
`with the gauge reads pressure only with respect to atmo-
`spheric pressure. As indicated by Fig. 2-12, a gauge which
`reads 0 pressure at sea level (atmospheric pressure) is actually
`measuring 1 bar on the absolute pressure scale.
`
`Absolute pressure scale
`
`1 bar (14.5 psi)
`
`0
`
`at sea level
`
`Standard pressure scale
`
`Atmospheric pressure
`
`Fig. 2-12. Calibration of pressure gauge influences how you
`interpret pressure readings.
`
`In any case. pressure values are always expressed in one or
`more of the following units or terms. All are correct. With the
`appropriate conversion factors. all are interchangeable. Fortu-
`nately, the math required to convert between the different units
`is simple.
`
`I Pounds-per-Square Inch (psi). The English system unit
`of pressure defined as force (pounds) divided by area
`(square inches). Atmospheric pressure at sea level is
`approximately 14.5 psi.
`
`0 Bar. A metric term derived from barometer or barometric
`pressure—acnospheric pressure. One bar is approxi-
`mately equal to standard atmospheric pressure at sea
`level, so 1 bar = 14.5 psi. Typical fuel pressure in a
`pulsed-injection system might be 2.5 bar, or about 36 psi.
`European manufacturers‘ specifications and pressure
`gauges usually refer to presaures in bar.
`
`0 kiloPascal (IrPa). The proper metric unit for pressure. 1
`bar = 100 kPa, so atmospheric pressure at sea level is
`tookFa. Used mainly in the US.
`
`0 Inches of Mercury (in. H9). Originally refers to measure-
`ment of pressure using a mercury manometer. (Hg is the
`chemical symbol for mercury). This is a term used to
`specify manifold vacuum; 29.92 in. Hg is the difference
`between standard atmospheric pressure at sea level and
`absolute vacuum.
`
`Table 3 lists the various units of pressure and appropriate
`conversion factors.
`
`Table a. Units of Pressure Conversion
`
`Atmospheric
`
`
`
`multiply by:
`
`if you watch the local TV weatherperson. you’ll see how
`barometric pressure readings (in. Hg) are used to describe
`atmospheric pressure changes. Listen to the references to
`“highs" and “lows". Changing atmospheric pressure changes
`the density of the air. Denser intake air can slightly alter the
`air-fuel ratio and may affect how your engine operates. Some
`Beech fuel-injection and enginemanagement systems have
`features which allow the system to compensate for variations in
`air density.
`
`Basic Factors
`
`

`

`ENGINE MANAGEMENT FUNDAMENTALS
`
`9
`
`'-
`
`Increasing load
`
`Using absolute pressure as the reference point, the piston
`on its intake stroke is creating a very low pressure in the
`cylinder—approaching zero absolute pressure. The pressure
`in the intake manifold —manitold absolute pressure (MAP) —-is
`higher and always a positive number. Higher still
`is atmo-
`spheric pressure outside the engine. its influence on manifold
`pressure controlled by the throttle. Boost from a turbocharger
`or supercharger is pressure above atmospheric pressure.
`Many European boost gauges read MAP. They are calibrated
`from zero absolute pressure 50. with the engine off. the gauge
`
`reads 1 bar—normal atmospheric pressure.
`
`
`I were talking about the requirements of a stationary
`it
`industrial engine. I‘d expect it to operate under basically fixed
`conditions: constant rpm. constant load. nearly constant tem-
`perature.
`limited stops and starts. no acceleration. and no
`heavy-footed driver. Such an engine would operate quite nicely
`at a fixed air—fuel ratio. It could be easily tuned to maximize fuel
`economy, and would require only the simplest ottuel systems.
`
`In. ”9-
`
`Cars. however. are a different story. We expect them to
`perform under the widest possible variety of operating condi~
`lions And we have given ”performance" a new definition it is
`not only impressive horsepower and torque, but also maximum
`fuel economy. and controlled exhaust emissions. As if these
`pertormance demands were not enough. we also expect the
`car to meet these demands effortlessly. at any time. under any
`cendilions. and at the turn of a key. We expect what has come
`to be called "driveability”—-the ability ot the car to provide
`smooth. trouble-tree perfonnanoe under virtually any condi-
`tions while delivering power. fuel economy. and controlled
`emissions
`
`Operating Conditions and Driveabiiity
`
`

`

`10
`
`ENGINE MANAGEMENT FUNDAMENTALS
`
`Cold Start
`
`This means the engine is cold; that is. it probably hasn't run
`for at least 12 hours. In most cases! the temperature needle is
`at the low end or the gauge. The engine might be as cold as
`—20“F {— 30°C). sometimes called cold—cold; or as hot as
`115°F (45°C). sometimes called warm-cotd. in either case, the
`engine is still cold compared to its normal operating tempera-
`ture of about 195°F (90°C).
`
`
`
`
`Fig. 3-1. Engineoold temperature varies according to out-
`side iemperature. Cold start means the engine has
`not run for several hours.
`
`Driveability is a term which evolved out of the early days of
`strict emission control and the “705 energy-crisis concerns over
`fuel economy. The lesstieveloped technology of the time dic—
`tated an approach to both problems which often resulted in the
`engine running too lean. Running too lean robbed power and
`contributed to rough idle, poor throttle response, stumbling
`and stalling, and overall poor running. Fuei injection and more
`complex engine-management systems offer the precise con—
`trol and flexibility necessary to meet modem performance
`requirements.
`
`To meet these demands under different operating condi-
`tions. the enginl has different air-fuel requirements. l'li discuss
`these operating conditions. the effect they have on basic air-
`fuel requirements, and how the capabilities of fuel-injection and
`enginemanagement systems are used to meet these require
`ments. I’m describing what these systems in general can do.
`not necessarily what a basic Jetronio fuel-injection system will
`do. particulady those systems on cars manufactured before
`1982.
`
`3.1 Normal (Warm) Cruise
`
`Normal cruising at light load with the engine fully warmed up
`is the baseline operating condition. The basic fuel system is
`designed to meet the engine's need for the proper air-fuel ratio
`under these simple cruising conditions. The design must be
`flexible enough to handle fuel deiivery at different speeds and
`loads. but this basic fuel metering is the fuel system‘s simplest
`task. Though the driver may add power on a hiil or to pass
`another car, or out back power to slow down. fuel management
`is still relatively simple. All other parts of the fuel system which
`compensate for different operating conditions do so by making
`adjustments to this main fuel-metering function.
`
`When you are cruising down the interstate. if the road is
`level the engine is operating under relatively constant normal
`conditions. The fuel quality may vary from one tank fill to the
`next; weather and outside temperature may change; it may be
`dry orit may be damp. The ideal air-fuel ratio will be different for
`each of these conditions. A fuel~injection system can adjust to
`these changing conditions with little chailenge. maintaining
`air-fuel delivery nearthe ideal (stoichiometric) ratio of 14.7:1 to
`satisfy the most important considerations of fuel economy and
`low exhaust emissions.
`
`3.2 Starting
`
`As an owner. you expect the engine to start instantly:
`whether it‘s at sub-zero temperatures or parked in the desert.
`too hotto touch: whether it's been sitting for five minutes at the
`store or for five weeks in the garage.
`
`As far as fuel system requirements are concerned. starting
`makes different demands depending on temperature. 1‘“ dis-
`cuss cold start. warm start. and hot start.
`
`Operating Conditions and Driveabirrgr
`
`

`

`ENGINE MANAGEMENT FUNDAMENTALS
`
`11
`
`
`
`
`
`Normal room
`temperature
`EPA cold—start
`test
`
`
`
`Warm-cold
`
`Fig. 3-2. Fuel requirement for engine starting varies accord—
`ing to outside air temperature: coldccld or wan-n—
`ccld. These temperatures are both coId compared
`to ncrrnal engine operating temperatures
`
`in most parts of the country. you will at times be faced with
`cold-cold starting conditions; the most challenging ofall. Gas-
`oline is less likely to vaporize when it is cold. Even if it is
`adequately vaporized. some fuel condenses on the cold parts
`of the engine before it can be burned. The engine requires
`extra fuel for starting so that.
`in spite of vaporization and
`condensation problems. the engine still receives a combustible
`air-fuel mixture.
`
`What constitutes a combustible mixture depends on air
`temperature. the volatility of the gasoline. altitude. barometric
`pressure and humidity. While a carburetor relies on a relatively
`crude choke mechanism to increase fuel delivery for cold
`starting. fuel injection compensates for many of these factors.
`Temperature is the most important.
`
`Gold-start enrichment quickly becomes a problem if the
`engine does not start right away; due to a marginal battery.
`ignition components in poor condition. or whatever. Enrich-
`ment during cranking must be cut back in a matter of seconds:
`ifit goes on too long, the air-fuel mixture will be too rich to ignite.
`The spark plugs may become fuel-fouled. particularly when
`they are cold, and the engine will not start.
`
`Cold starting also needs help in terms of intake air flow. A
`closed throttle and slow cranking speeds do not allow enough
`air for starting. Drivers of carbureted cars develop intricate
`starting procedures: depress the accelerator to the floor. re-
`lease. then hold the throttle about 1/5 open (for example). The
`first depression is necessary to set the carburetor choke and
`fast-idle cams; the second is to open the throttle and make sure
`the engine is getting enough air. Fuel-injection systems can
`control the air by bypassing the closed throttle, admitting more
`air when cold without any effort or attention from the driver.
`
`
`
`Warm Start
`
`Warm starting is very much like wann running. The air-fuel
`demands are simple. A warm engine helps promote fuel va-
`porization. and fuel is much less likely to condense out of the
`air stream onto warm engine parts
`
`Depending on the temperature. the engine may benefit
`from some small portion of the usual cold-start compensations.
`A carbureted car may benefit from a light push on the throttle.
`using the accelerator pump to deliver a little extra fuel. A
`fuel-injection system sensing temperature only a little below
`normal may just slightly enrich the mixture and slightly increase
`intake air to improve wan-n starting.
`
`Hot Start
`
`This means the engine is hot; perhaps after being driven for
`some time on a hot day. and then allowed to sit for a short time,
`unable to significantly cool. Underthese conditions, sometimes
`called "hot soak” under-hood temperatures may exceed 250“F
`(120°C).
`
`The most important aspect of hot soak and subsequent hot
`starting is the possibility of overheating the fuel. For a carbu-
`reted engine this may mean boiling the fuel in the fuel bowl and
`losing it as fuel vapor into the atmosphere. Hot starting be-