Volvo 819 E User manual

700
1982-
Section 2(28)
Ignition systems
TP 31397/1
July 1989

This manual deals with the following engine variants :
Engine Model year (s) Engine Model year(s)
819 E1984 B230 FT 1985-
B 23 E1984 B230 K 1985-
B 23 FT 1984-88 B200 E 1985-
B28 A1982-85 B200 K 1985-
B28 ElF 1982-86 B280 ElF 1986-
B230 A1985-86 B204 E 1989-
8230E 1985- 8234F 1988-
B230 F 1985-
Volvos are sold in versions adapted for differentmarkets.
These adaptations
depend on many factors including le-
gal,
taxation and market requirements.
This manual
may therefore show illustrations and text
wh ich do not applytocarsin you r coun try.
Volvo
owners planning to expo rt their carls) toanother
country should investigate the applicable safety and ex-
haust
emission requirements .In some cases it may be im-
possible to comply with these requirements.

3
Group 28 Ignition systems
Contents
Group 28 I gnition systems
Contents
Page
Introduction .
Design and function:
Overview
Review of electronic ignition systems -I .............................•........... 4
Review
of electronic ignition systems - II (type EZ-K and Rex -J) .. ..... .•. .. .•......6
General
Function of ignition system; combustion theory in brief ....... . ..... ... . .. ........ 9
Ignition systems -basic parameters. . .. ........ ........ .... .......•. . . . •. . ..... .. 11
Contact-breaker versus electronic systems ...................... . .. •....•. ........ 13
Components
Control unit ..................................................... ..... .... 14
Control
unit , power stage and i gn it ion coil configura tion s.................. 16
Power stage and
ignition coil.. .. .. .. .. ... .. ...... .. .. .. ...... .•. ..•• . .•. .. .. . ... 17
Dis tributor ............... . ..............................................•....... 19
Speed and crankshaft po sition information
Hall generator ....................... ... .. .. .. .. .. .. .. .. .. .. .. .. .. . •. . . . •. . . . . .. 20
Speed/position pick-up
and flywheel configuration 22
Load information
Induction manifold vacuum .. .. .. .. .. .. .. ........ .....................• .. ...... .. 25
Fuel
injection system control unit.. .................... . .•.. ..... .... .•. ....... .. 26
Compensation functions
Theory of knock. ......... ......... .. . •. . . . ................... 28
Knock sensor ...... .... ...................... . ....... . ..•.... . ....... . .......... 30
Knock control
................................•.......•...... . •.......•.......... 32
Knock-con
trolled fuel enrichment ..................•. . .... . ... .. ... • .... • ..... 39
Throttle switch li dling switch ............... . ....... . ....... . .. • .......•....•..... 40
Temperature sensor
.............................. .• ..•... . •..•.......•... •• ..... 41
Ren ix· F. . .. .. . .. .. .. •. . .. .. .•. . .. .. .•. .. .. . •.......................•...........
EZ·l02K .. . ....•.... • ....... • .... . ..•.... . ..•....... . ..•... .. ..•.... . ....•......
EZ -1 17K .......•....•.... . .. . .... . .. .. ... . .. • .......•..•.... . ..•.... . .... . ......
EZ -118K .........................•....... . ....... . ....... . ....... . .......•......
EZ -115K ............ . ......... .. ..•. .. .... . .. • ... ... . .....•....•......
EZ - 116K. ...................... .... ..... . .. •. ..•... •.. .....•....•..
Rex·1 ............ .... .................. .. .. .. ....... •. ... ..
Diagnost ic system, EZ -116K and Rex-I .
System descriptions
TSZ .. .. . .. .. . ... . .. . . .. .... . ... . ...•.
TZ-28H .............................•...
.43
44
45
47
4"
51
55
58
60
63

Group 28 Ignit i on systems
Contents
Test equi pment ...... • ....•.... • ..•...••..•...... . •..•......••..•....•.......... 68
I
nstruct i ons ............................•. . . . . . . •. . •. . •. .. .. .. •. . . . •. . •........ .. 69
Specifications
......................•....•.. , ...• • ..•..•....... • ... • •........ 71 -78
Bre .kerless ign iti on syst ems ........... • ..•.... • .. • ..•.......•....... • .......... 79
Fault
tracing ...... ... ........ ... .. • .. •...., .. • .. •.. .. , .. •. .•. . ..•.. •. ...... . .... 105
TSZ-4....
.... . .... . ... . ... ...... .•. .. .. .. •..•.. .. ..,•.. •. ... .. .• ...••. . ..... . ,. 106
Aenix·F
.. ... .... .... .• .... • .......•...... . •..•....... • .. • ..... . .•.......•.. . .... 115
TZ·28H
.. . ........ • ..•.•..•.......•.......•..........•.. • ....... • ....•... . ...... 125
EZ - l02K .............•... •• .. • ....•... • •.. • ..•. _. ••••• ..•..•.... • ..• • •... • ...... 135
EZ -115K ..........•.. • ....•... . •.. • ....•.. • .......•.. • ..•....• ..• ....•.......... 151
EZ ·117/118K _• ....•....... • ....... • .......... • ..•.... .. •• .......•.......... 169
EZ·116K 187
Aex-I
............. ... ........ ... ....... .... .. ....... .. .. ..••. ..... ...... . .. . .... 21 5
See Service Manual. Fault
tr acing, repair and maintenance, Section 2(23), B 23, B200,
B230 ET E ngines .740,760 Turbo, for details of Motronic systems.(Order No . TP 30949/ 1)
Index, page 227
Order No .: TP 31397/1
Supersedes TPI31059/1USA
We reserve the right to make changes
w ithout prio r notificatio n
2e
VOlVO NORTH AMERICA CORPORATION

Group 28 Igni t ion sys t ems
Introduction
Introduction
Comprehensive development work by Volvo has resulted in the design of engines boast ing high performan ce, low
fuel consumption, cleaner exhaust gases, a high standard of reliability and simplifie dservice procedures. The ever-
increasing use
of microelectronics for the control and regulation of igni ti on and fuel systems has been one of the
most sign if icantfactors in this development.
Compared with their mechanical counte rpart s, elect ronic (or microprocessor-controlled) ignition systems offer ad-
vantages such as greater r eliability, optimum timing under all driv ing co nditions and few moving parts, reducing
service requirements toa minimum .Asaresult, Volvo has, in recent years, co mp letely replaced itsr elatively simple,
mechanically -controlled, contact-breaker systems with sophisticated s ystems controlled by microprocessors and
electronics.
Equ
ipping system control units with various additional program functions, and integrating them with other control
systems and componen ts ,has enabled traditional ignition systems 10 be augmented by features such as temper-
ature-eompensated timing for faster engine warm-up , improved exhaust gas composition and lower working tem-
perature . Other functions which may be con troll ed by an electronic i gnition system control unit include fuel cut-off
under engine braking (deceleration) conditions and igni tion retardation in individual cylinders to eliminate knock .
Volvo
markets a wide range of models with aseries of engine options. This , combined with rapid developments in
the field of electronics , means that a wide variety of electronic ignition systems of different types and degrees of re-
finement now exist .
Systems
of thi s type impose completely new demands on fault-tracing procedures.A certain basic understanding of
the input and ou tput signals, the manner in which the componen tsare connected and the fun c tion/purpose of each
is essential
to an understanding of the types of fault which may arise, and to ensuring that the co rrect diagnosis is
made in each case.
Sensors
and pick-ups providing fast and precise info rmation on the prevailing running conditions are vital to ensure
that the electronics con trol t he working componen ts of the system rel iably and accurately.
This manual deals with the electronic igni t ion sys tems used by Volvo on its700 series models, in terms of design
and function , as well as fault tracing, repair and maintenance. The fir stpart of the manual consists of a description of
the features, components and compensation functions common to the various systems, followed by a description of
each individual system and some of the special functions peculiar to each. The appropriate wi ring di agrams arein-
cluded.
3

Group 28 Ignit;on systems
Design and function - Overview
Review of electronic ignition systems - I
A B CDEFGH
;; lJ
trn
~ ~
TZ-
~
';"
28"
~ ··oc
~ '
~
IlENIX
a
~ ~
~
F
147 077
The above figure shows the major componen ts of each of the systems descri bed below .
Summary
Control system
The control unit (A) house s the electronic circuits and the various program functions nee ded to compute the timing .
The
power stage (Bl cont r ols the pr i mary current in t he ignition coil in response to con trol signals fr om the control
unit. The power stage may either be an integral part of the control unit or aseparate unit assembled with it. The func-
t ion of the distr i butor (e) is to deliver t he high-tension pulse i ndu ced in the secondary winding of the ignition coil to
the correct spark plug . The distr i butor may be dr i ven ei ther by bevel ge aring (in whi chcase itis ins talled vertically) or
directly from the camshaft ( hor i zontally i nstalled units) .In systems in which the rotor arm is the only moving part
(such as
types which employ inductive speed pick- ups ) the lim ing ca nnot be varied by alter i ng the pos it io n of the
distributor .
Sensors
The rema ining components in the tab le (D-E)c omprise part of the senso r system. T ogethe r with the con tro l un it,
these
supply i nformat io n on prevailing engine running c onditions .
Bas ic parameters
The con trol unit is supplied with information on engine speedand crankshaft position (D) either by aHall generator
activated by a trigger rotor (with four vanes) moun t ed on the rotor s haft or by an inductive pick- up mounted c lose to
the
flywheel (on manuals ) or ca rrier pIaIe (automatics) .In th is case, the periphery of the flywheel /c arrier plate is pro-
vided with aseries of holes whose passage is detected by the p ick-up and ind icated in the form of electrical signals.
The
eng ine load (E) is measured either by means of a vacuum line anached to th ei ntake manifold or, if the eng ine is
equipped wi th an LH-J etron ic fuel inject io n system (i.e. most engine sequi pped with EZ-Ki gnit i on systems ). by an
airmass
meter (see next ill ustration ). The var ious signals - engine speed, crankshaft posi tion and enQine load -
com pr ise information which is used by ignit i on systems ofall types to compu te the tim ing.
4

Group 28 Ignition systems
Design and function - Overview
Review of electronic ignition systems -I
TSZ :An electronic ignition system in which the function performed by contact breaker points in conventional sys-
tems is carried out by an induc tive pulse generator. (Roughly translated, the abbreviation TSZ - which stands for
Transistor Spolen lundung - means 'Transistorized coil ignition'.) The pulse generator signals are transmitted to a
'co ntrol unit'which regulates the coil charging period. Thesystem also inco rporate sacent rifugal generator and a
baltast resistor. Designated TSl-4, the variant for 6-cylinder engines (B28A1EiF)was used on 700 series cars from
1982 to 1986.
TZ ·28H: As the designat i on indicates , this is a trans i stor ized system employ i ng aHall generator to supply the si gnals
used by the ' control unit' to c ontrol the pr i mary current in the ign i tion coil. A vacuum advance un it on the distributor
varies the timing with engine load . Although t he sys tem was used on some 700 series models produced in 1984,it
was almost completely superseded by other systems in 1985 as the new family of engines entered production . (Un-
like other systems discussed in this con text ,TZ-28H is not fully electronic; indeed. it is usually regarded as one of the
group of transistorized systems .)
RfNIX-F: The name isa trademark of the Bendix company .In this system , the contro l unit. power stage and ignition
coil comprise a single un it.Since '985 ,Renix-F has been used on 7405 equ i pped with the B200 K engine and Salex
c.rburettor.
• The letters used in the deS i gnations 01 the var i ous systems are u sually derived from the maker 's nat ive l anguage . wh i le the fig -
ures usually denote the ver Si on and/or var i ant design ation .
5

Group 28 Ignition systems
Design and function - Overview
Review of electronic ignition systems - II
(Type EZ-K and Rex-I)
ABC0EFGH
~ ~
Ud'"
--
tJJ
EZ-
I ' \..~
['\l .
~
~
(3P
G
102K
u-
1m
I /'~
~
~ '"
~
(jf
EZ-
\' \ ~
~
0
117K
~ l ... ."
U-"
~
,
($
~
r.v
~
0
~
q
EZ-
~ ) ~
118K
~
]I
~
n,
q
EZ-
/'
b
~
a
115K
~
&,
u:.-'
EZ-
[ij
0
~
b
~
CJ
ad
116K
('
-$
~
iii
QJ q
REX-
\J b
I ~ , ')
I
141071
The illustration shows the main components of type EZ -K and Aex-I ignition systems .
Common features :
An
abbreviation of the German term Elektronischer Zundung mit K lo pfregulung (roughly, ' Electronic ignition with
knock
sensor ') the designat io nEZ-Kdescribes a group of systems manufactured by the Bosch company. The various
systems in the EZ-K group are relati vely similar in terms of functions and components. All feature microprocessor
control and inco rporate a memory which is programmed with a family of ideal timing curves for the particular en-
gine. Each
system also includes a sensor which detects engine knock and retards the ignition in respon se to a mem -
ory program which is indiv idu al to each cylinder. This means that the timing in each cylinder may vary at any given
instant.
As column Eindicates, systems in this group are normally supplied wi th engine load information by an air mass
meter located in the in take system. A measure of the quantity of air supplied to the engine , the air mass meter signal
is
transmitted to the LH-Jetron ic control un it(in which it is converted and used to determine the quantity of fuel to be
injected) and then to the ignition system control un it.
Differences
Within the EZ -K group, the individual systems are distinguished by t he timing curves used for different engine var -
iants, by whether aHall generator or inductive speed/ position pick-up is used, and by when the ignition compensa-
tion functions are activated.
6

Group 28 Ignition systems
Des ign and function - Overview
Review of electronic ignition systems - II
EZ - l02K was i ntrodu ced in 1984 in conjunction with the launch of the 760 Turbo with the 823 FT engine and lH 2.1
fuel injection system on the American market. EZ-102K is equipped with a thermostat which transmits a signal to
one
of the control unit terminals when the engine temperature becomes excessive. commanding it to advance the
timing if the throWe isclosed. The first EZ -Ksystem to be used by Volvo, EZ -102K remained in production only for a
year before
be i ng superseded by more up-to-date variants according as the new family of engines was introduced.
EZ-117K is very similar to EZ -102K in configuration, although designed for the 8230 F and 8230 FT engines with the
lH..Jetronic 2.2 fuel injection system. The system was introduced with the new family of engines in 1985. The
8230 FT variant features a knock-controlled fuel enrichment function . like its predecessor, EZ -102K,the turbo engine
variant is equipped wi th a thermostat which activates a timing advance function to protect the engine from over-
heating.
EZ -118K differs most from the other systems in the group . due to the fact that it depends on a vacuum connec tion be-
tween the intake manifold and control un it to supply engine load i nformation ,rather than on a load signal supplied
by an air mass meter via the fuel system control unit. The system also emp loys an idling switch mounted on the
thr o ttl e pulley rather than as witch mounted on the throttle housing . EZ -118K was introduced in 1985 on the B200 E.
8230 Eand B230 Kengines. Tw o idling compensation functions may be used on all E Z-1 18K variant s. The 82 30K
variants are
equipped with a temperature sensor, while the co ntrol unit operates asol enoid valve which inte rr upt s
the fuel
supp ly under engine braking conditions. Most of the differences are a ttributable toth efact t ha tthe system is
used on carburated engines (now with Pierburg carb urettor s) and on E engines with the CI system (K-Je tronicl.
EZ -115K has been designed especially for the 8280 engine. Its features include two kn oc ksensors (one for each bank
of cylinders), a position detector for No .1 cylinde r,aknock-controlled fuel enrichment function and an induct ive
speedJposition pick-up
mounted at the flywheel. Depending on the temperature sensor signal. t he control un itcan
apply tim i ng compensation by retarding the ignition when the engine is cold toachieve faster heating of the coolant .
and
by advancing it when the engine tends to run too hot. The sys tem appeared in 1987 with the in troduct ion of the
8280 engine to replace the B28,and is, therefore,used only on the 760/780. EZ-1 15K is used in combination with LH-
Jetronic 2.2on both the Eand Fvariants.
EZ-116K is a
refinement of other EZ -Ksystems. However, it features advanced self-diagnostics which facilitate fault
tracing and monitoring .The control unit continuously mon i tors the various sensors and functions , and any faults
present may be displayed with the aid of adi agnostic un it mounted in the engine compartment. EZ -116K was in-
troduced in1988 on the 1&va lv e 8234F engine used in the 740 GlT . Unl i ke other EZ-K systems used on 4-cyl inder
engines in the 700 series, EZ -116K is equipped with an induc tive speedJposition pick-up mounted close to the fly-
wheel instead of aHall generator in the distributor .The system is used in combina ti on with the very latest fuel in-
jection system (LH·Je troni c2. 41 .
Manufac
tured by 8endix ,the Rex-I system is equipped with the same type of diagnostic system as EZ-116K. Used in
conjunction with the Regina fuel injection system, Rex-I was introduced in 1989 on 8230 F engines sold in theUSA.
Compensation functions
However, most electronic ignition systems are equipped with addi ti onalsensors which enable thecontr ol unit toad-
just the timing to compensate for unusual running conditions. Thus. sensors ( F-H ) may be regarded as pr oviding the
ignition system with compensa tion functions. In the event of engine knock (the phenomenon whereby thefuel/ air
mixture is ignited by asource other than the spark plug), the kn ock sensor (FI moun t ed on the engine wi ll transmit a
signal to the
control unit commanding it toretard the igni tion. Complete closure of the throttle is indica ted by a throt -
tle
switchlidling switch ( G). When the engine is idling. the control unit regulates the t iming in accordance wi than
'i
dling program ' to ensure optimum co mfort , while the t iming under engine braking condi ti ons is controlled to mini-
mize exhaust emissions. The signal supplied to the control unit by the temperature sensorhhermostat enables the
un it to apply the appropriate ti ming co mpensat io n when the engine temperature is unusually hi gh or low.
7

Group 28 Ignition systems
Design and function Overview
IGNITION SYSTEM
TSZ-4
TSZ-4
TSZ-4
TZ-28H
TZ-28H
TZ-28H
MOTRON'C
MOTRONIC
MOTRONIC
RENIX-F
REX-I
EZ - l02K
EZ - l17K
EZ · l17K
EZ -118K
EZ -118K
EZ - 11 8K
EZ·'18K
EZ- 11 5K
EZ ·115K
EZ -1 16K
EZ -116K
EZ·116K
ENGINE
B28 A
B28 E
B28 F
B19 E
B23 E
B230 A
B23
ET
8200 ET
B230 ET
B200 K
B230 F
B23 FT
8230 F
B230
FT
B200 E
B230 E
B230 K
B230 K
B280 E
B280 F
B234 F
B230 F
B204 E
YEAR
82-85
82-86
82-86
84
B4
8!">-S6
B4
85-
85-
85-
89-
84 (USA)
8!">-S8
85-
85-
85-
85-86
87-
87-
87-
88-
89-
89-
N.B.Due to differences in model specifications from country to country.the number of controlunit variants used for
the various ignition systems and engines may exceed that listed above.
8

Group 28 Ignition systems
Design and function - General
General
cB
o
A
Function of ignition system; combustion theory in brief
Correct ignition tim ing
A.The function of the ignition system is to ignite the compressed fuel/air mixture in each cylinder at exactly the cor-
rect
instant . Ignition is followed by the propagation of a flame fr ont through the combustion chamber until the com-
plete ch arge hasbeen burned. The combustion pressure. whi chis higher than that of the comp ressed mix ture, gen-
erates a high f orce whi ch drives the pis t on downwards in the cylinder. (Al thou gh a proportion of the energy released
is
converted into mechanical work by the crankshaft, most of the energy in the fuel (approx. 70%) is dissipated in the
form of cooting losses, exhaust gas losses and mechanical losses.)
To ensure that the igni ti on timing is as close as possible to the 'co rrect' setting under all runn i ng conditions, the tim-
ing must be adjusted continuously to take account of variations in the conditions. In other words , the optimum tim-
ing is not a fixed sett i ng for each eng i ne , but varies with factors such as engine speed, load, fuel/ air ratio and temper -
ature . Furthermore , the timi ng may be ad jus ted for optimum comfort, maximum torQue or maximum power as ap -
propriate .
In
the rest of this discussion , the term optimum tim i ng shall be taken to mean a setting which takes account of all the
factors influenced by the ignition. In other words ,it is a compromise between the demands of high power , low fuel
consumption and the cleanest possible exhaust emissions. The emergence of ever-stricter emission s tandards has
been
the main factor in the development of igni t ion systems designed to optimize the combus tion process under all
running condi tions.
Earlv ignition
B.Early ignition prevents efficien t expansion of the fuel/ air mixture since the piston is s ti ll travelling upwards to-
wards TOC as the pressure rise occurs, generating an abnormally high pressure accompanied by an excessive tem-
perature rise.As a
consequence of early ignition, part of the unburnt fuel/a ir mixture may i gnite spontaneously,
causing the engine to knock .
In general,
early ignition also has an adverse effect on the exhaust emissions. The Quantity of unburnt hydrocarbons
( HC )increases, while the pressure and temperature rises cause the nitrogen in the trapped air to react wi th the
oxygen to fOfm greater quantities of nitrogen monoxide (NO) and nitrogen dioxide (NO) Of NO .. oxides of nitrogen) .
9

Group 28 Ignition systems
De sign and function General
ABc
late ignition
C. Late ign it ion reduces engine power since the pis t on is t ravelling downwards from ToC when the pr essure rise oc-
curs.
As a result , the engine does not utilize the full energy content of the fuel . Although the concentra tions of unde -
s
ira ble constituents such as HC, CO, NO and N0
2are
lower under these conditions, the engi ne require s more fuel to
deliver the same outpu t, producing a greater tota l volume of exhaust gases.
Effects on cylinder and exhaust gas temperatures
Advancing the ignition (i.e. generating the spark to ign ite the fuel /air mixture when the pis ton is further from ToC )
produ ces ah igher combustion temperature and a low er exhaust gas temperature than when the tim ing is reta rd ed.
Thisis
due to the fact that the compression produced by upward movement of the pis t on reinforces the pressure
wave developed by t he flame front, causing the cylinder pressure and temperature to increase. The lower ex hau st
gas
temperature is explained by the somewhat longer interval between the completion of combustion and th e open-
i ng of the exhaust valve.
Re
tard ing the igni t ion (gene rating t he spark when the piston is close r to TD C) produces alo wer comb us ti on t em per -
a
ture ,buta higher exhaus t gas temperature than when the timing is advanced. Under these condi tio ns , a hig her pro-
portion of t he energy is released during the expansion stro ke (when the piston is moving downwards), r educin g the
maximum temperature somewhat. The higher exhaus tgas t emperature is explained by the shorterinterval between
the comple ti on of combustion and t he opening of the exhaus tvalve.
-NOTE ;It is important that the follo wing terms be clearly understood in orderto avoidconfusion:
a) Advancing the ignition timing means that the ignition pulse is delivered when the piston is at apoint funher from TOC.
b) Retarding the ignition means that the ignition pulse is delivered when the piston is at apoint closer to TOC .
•Under normal conditions, the aim is to develop 'peak' pressure in the cylinder about
10 "after TOC. Under idling conditions, the
timing
is advanced (toapprox. 10-15"before TOC) to ensure smooth running.
•
The foregoing discussion of how the emissions are affected by th eignition timing is somewhat simplified, since there are natural·
Iy many other factors which influence th ecomposition of the exhaust gases.
10

Group 28 Ignition systems
Design and function - General
B
A¢ \ co
147080
II I111
Ignition systems - basic parameters
The ignition system control unit must be supplied with certain basic information in order to compute the frequency
or rate atwhich HT ignition pulses must be delivered to the spark plugs, when (in relation to the position of t he par-
ticular
piston before TOG) each pulse must be generated and to which plug the pulse is to be delivered. The signals
requi red for this purpose are derived from the engine speed (A), engine load (B) and crankshaft position (G).
Speed information
A.T he engine speed provides information on the number of ignition pulses which must be generated per unit of
time. The number of high-tension (HT) pulses delivered to the plugs must be increased as the engine speed rises.
The speed
signal is the most vital piece of information supplied to the control unit. For example, the engine cannot
be started in this signal is unavailable.
The
control unit a lso uses the engine speed to determine the point at which the ignition pulse must be delivered in
r
elation to the position of the piston before TOG. Ignition must take place earlier at higher speeds since the upward
and d ownward movement of the pistons is faster under these conditions. As aresult, the time available for combus-
tion of the fuel/ air mixture is less and the timing must be advanced to ensure that the mixture is burned as comple te-
ly
as possible.
Load information
B.Except in turbocharged engines, the engine load varies with the vacuum in the intake manifold. At low loads, the
th r ott leis only partially open and the flow of induction air is low, resulting in a high vacuum. At higher loads, the
thro ttl e opens wider and more air is supplied to the engine. Under these conditions, the vacuum in the manifold ap-
proaches
closer to atmospheric pressure as the load is increased. It follows from this that a greater quantity of fuel/
air mixture is available for combustion as engine load increases and that the higher volume of gas produced rein-
forces the pressure
due to compression. Since the rate of combustion is accelerated by higher gas compression, the
t iming is retarded as engine load is increased. At low engine loads, on the other hand. the timing may be advanced
to
compensate for the low er rate of combus t ion and to improve fuel utilization.
Crankshaft po s ition information
C. The crankshaft position (i.e. angle ) provides information on the position of each piston in relat ion to TOC. This in-
formation is essential to the system control functions. which compute the timing continuously on this basis.
11

Group 28 Ignition systems
Des ig n and funct ion - General
Fig. 1'Hot' plug Fig. 2'Cold' plug
147081
• Spark plugs :Use of the correct type of spark plug, correctly ins ta lled and replaced at th ere commen ded in tervals ,
is
essential to t he satisfactory operation of the ign it ion system. Assuming the engine to be in good co ndition , ad -
herence to these recommendations will ensure maximum plug life, making the component one of the most re-
liable in the ignition sys tem .
In
this context, it may be of interest to consi der some of the demands impose don the spark plugs and to discuss a
number of concep ts.
- As the means used to igni te the mixture in the combustion chamber, the spar k plug in it iates the co mb us t ion pro-
cess. The plugs are designed to supply up to approx. 25 sparks per second per cylinder at 6000 rlmin in a4-c ylinder
e ngine , from a high-tension source which, in the case of electronic ig nition systems, often operates at over 30 kV .
-
Spark plugs must be capable of withstanding the extremely rapid temperature and pressure flu ctu ation s which oc-
cur in the combustion chamber. During the combustion process, th e temperature rises at in terval stoa value of
perhaps 2500"C and the pressure to approx. 60bar ( 870 psi). Almost immediately, during the induction stro ke, the plug
co mes in contact with the cold, un co mpressed fuel lair mixture , which is likely tobe at the same temperature as the
outside air.
-To e
nsure operation within th e correct operating temperature range, spark plugs are made wit h different heat rat·
i
ng s(orranges) for different engine types . If the operating temperature is too low (i.e. below about 400QC), the plug
will rapidly become coated with combustion residues. This type of fouling weakens the spark and ca uses the en-
gine to miss. On the other hand, if the opera ti ng temperature is t oo hig h (ove r approx . 1000 ~ C), the fuellair mixture
may be ignited by the in candescen t plug surfaces, initiating uncontrolled combus t ion. Every engine manufacturer
specifies the app r opriate heat rat ing on the basis of parameters such as sp ecific engi ne output, probable runn i ng
conditions and clima tic conditions.
-A plug with a high heat rat ing has agreater thermal retention capacity and conducts less heat away from the com-
bustion chamber. This type is normally used on low-speed engines operating at relatively low com bustion tem -
peratures.
Plugs of t his type are also known as 'hot' plugs and are provid ed with a long insula tor nose as shown in
Fig.1.
-A
spark plug with a low heat rating has a lower thermal retention capacity and conduc ts a grea ter amount of heat
away from the combus t ion chamber. This type is normally used on engines with high specific outpu ts operating at
relat ively high combustion temperatures . Plugs of thi s typ e are also kn own as 'co ld' plugs and feature a short in ·
sula t or nose as shown in Fig. 2.
- Fitting a plug with the recommended heat rating will ensure that the correct working temperature is reached quick -
ly wi
thout t he r isk of overhea t ing. This also assumes that the t igh t ening torque is within the speci fied limit s, since
the thermal conductivity will be dependent on th e degree of contact be tw een the cylinder head and plug . The
spark gap should also be checked; an excessive gap will cause the engi ne to miss.
12

Group 28 Ignition systems
Design and function - General
0· 1 0" ---=:J; ~~
L-...l -10 -20 -30 - ~O - 50
°
2
1
A
' 0·
Contact-breake r versus electronic systems
Figure {AI shows the tim ing curve for acon tact -breaker ignition system, wh ile (BI illustrates the settings with wh ich
an
electronic system is programmed , in the form of a three - dimensional map _In each case, both engine speed and
load are taken into account when determining the setting . However ,in co ntrast with the electronic system, which
computes the t iming, the con ta ct-breaker system controls it wi thin aspecified range.
The timing must be con trolled to a high degree of accuracy to meet the demands of the modern engine for the clean-
es t possib leexhaust emissions, maximum fuel economy and high performance under fluc tuating condi tions.
N
either may the se requirements be permitted to vary, even following an extended period of driving .
Timing curve symbols
Both figures illustrate the manner in whi ch the t iming angle {al varies wi th the engine speed (n) and the va cu um (pi
in the intake man i fo ld. The ang le (a) increases with speed;in other word s, igni t ion of the fuel/air mixture takes place
earlier
as the speed rises. The angle also increases wi th the vacuum in the intake manifold i.e. as the eng ine load falls
and
the fuel/air charge supplied to the engine becomes smaller .
Contact-breaker ignition systems
A.Co nt ac t-breaker ignition systems con trol the timing with the aid of a centrif ugal governor (1) and a vacuum ad-
vance
un it(2). (Being a speed - dependent device , the governor advances the ignition as the speedincreases, while
the vacuum advance unit retards it as the engine load increases in response to the vacuum signal from the intake
manifold .) T he two devices operate independently wi thin a tol erance band of approx . 2-4 ". Overall, this means that
the system controls the tim ing with in a to l eran ce range of approx. 4-8" ,since the setting is the sum of the angles in-
dicated
by the two curves. Furthermore , the variat i on wh ich results from wear of the breaker points affects the over-
all t
iming.
Electronic ignition systems :
B. The co ntrol unit ( 3) of an electronic ignit i on system, by contrast, is programmed wi th aseries of specific settings
f or a number of defined speeds and engine loads.This means that the timing can be controlled to an accuracy as
h igh 8S 8fraction of a degree and thateach ignit ionpulse is delivered as close as pos sibleto the op ti mum point.
( Thi s high level of accuracy is achieved partly by the fact that the con trol unit interpola tes between the programmed
speed and load points .In other words , it is capable of computing an intermediate setting.) Furthermore , the timing
can be com put ed over a wider range and is not restricted by the type of linear functions typ ical of a centrifugal gov -
ernor .
The t iming is computed with th eaidof sensors wh ich determine the engine load and speed. Th is in format io nis
transmitted electrically to the control unit electronics, in wh ich details ofa number of different speed and load com-
binations , together with the appropriate t iming se tt ings, are s tored . Pr i or to each igni ti on pulse , the control unit com-
putes a setting wh ichis perfectly mat ched to the engine running co nd i tion s prevailing at the precise instant .
Adjustments required by the various timing co mpensation fun c tions are added to the three - dimensional map.
13

Group 28 Ignition systems
Design and function - Components
Bc
Components
Control un it
The control unit in an electronic ignition system continuously computes the optimum timing based on information
supplied by the various sensors, which combine to provide the unit with an extremely accurate picture of engine run-
n ing co nditions. The con tro l unit receives immediate notice of any change in the conditions under which the engine
is powering the car, enabling it to compute a new setting instantaneously. Once this has been completed (in an oper-
ation taking as little as a thousandth of asecond!), the unit delivers an ignition pulse to the power stage.
The
control unit consists of a number of electronic components. In simplified terms, these consist of four main ele-
ments - converter (A), memory (B), microprocessor (chip) (C) and output unit (D).
Co nv e rt er
A. The converter (A) receives information from the sensors and converts the signals into digital (n umerical) form.
Some of the sensors supply analogue signals (such as the temperature-dependent change in resistance typical of a
temperature sensor), while the signal transmitted by others depends on whether or not a voltage is present (as in the
case of a throttle switch). The sensors may also transmit signals in the form of voltage pulses (like an inductive pick-
up)
or a variable-frequency voltage (like aload signal vacuum converter). All of these electrical signals, whe t her in
the form of asingle, variable voltage or aseries of voltage pulses, are converted into standard digital form by the
converter, the outputs from which are used by the microprocessor and memory.
Memory
B.All programs and pre -programmed values are stored in the memory (B), in which all possible values of para-
meters such as engine load and speed are available for immediate use by the microprocessor.
Micropr oce ssor
c. The microprocessor (C) receives the digital signals from the converter. Depending on the signal configuration, the
device selects the memory program which best meets the needs of the prevailing running conditions.
14

Group 28 Ign it ion systems
D esign and function - Components
Output unit
D. The digital information supplied by the microprocessor is fed 10 the output unit (D) for conversion in to the ignition
pu lses fed to th e power stage . (This may either be an integral part of t he control unit or a separate uni t.)
Depend ing on th e program selected at t he particular instant, t he con trol unit de t ermines the p oin t at which t he igni·
tion pul se must be delivered to t he power stage. The la tt er con t rols the current in the primary winding of th e ignition
coi l in re sponse to the signa lsf rom th e output unit.
Voltage stabilizer
The con trol unit is powered by a12 V supply. However , since the ba he ry voltage is too high for the internal integ rat ed
circuits ,a vol tag e stabilizer is used to produ ce a stabilized 5 V supply for these .
•Engine speed
limitation: All control units are programmed with some type of speed limiting function. On Bend ix systems, the
conlrol unit normally commands the power stage to reduce the Ignition coil charging period. producing a weaker spark which
limils the eng i ne output .On EZ-K systems, Ihe conlroi unit uses Ihe power slage 10 interrupl l he spark 10 every second plug. The
speed limiting funct ion normally inlervenes at aboul 6200 r/min.
In the case ofcars equipped with Fengines, the speed limiting function controlled by Ihe ignition syslem control unil is set to op-
erate 81 a higher level than thaI controlled by its fuel system counlerpart. This prevents unbu rnl fuel from reaching Ihe catal yti c
converter,
with the a nendant risk of overheating.
•
The control unit memory is programmed with arange of speed and load values. The unit improves the accuracy of control by in-
terpolating between Ihese values, performing up to about 1ססoo compu tation s per minute to ensure that optimum l imi ng is
maintained under all conditions . As many as 4000 individual settings may be computed as required.
•Built
from components such as integrated circuits ,transistors, diodes and capacItOrs,electronic componen ts like the control unit
are relatively fragile.Since the electronics used in cars are exposed to such a diversity of operating conditions, they are subject to
particularly arduous demands .The equipment mUSI be designed to withstand vibrations. moisture, wide temperature fluctu -
ati
ons , variable voltages and other sources of outside interference (e.g. from rad iosl to which the electrical system is unavoidably
exposed.
•
In th e case of certain internal fault s, the control unit regulates the ignition in accordance with a fixed. pre-programmed timing
curve.
•
In Ih eabsence of aload signal, Ihe con trol unit modifies the timing on the basis of the speed signals which it receives, and ope r-
ates in accordance
with the pre-programmed. full -load timing selling when the idling switch has opened.
• If the knock sensor signal is lost. the con lrol unit com putes the timing setting on Ihe basisofa'fail-safe' retardation of approx. 10".
•The
control unil electronics must not be exposed to excessively h ig htemperatures.For example, removal of the unit prior to the
completion of the stoving process during manufacture may result in its destruction .Because of its sensitivity to temperature, the
unit is normally installed in alocation well protected from engine heal.
15

Group 28 Ignition systems
Design and function - Components
A,-
• JD
~ [
•
B
ci
~
:oJ
JI
-J
'"
Ui
D
Control unit, power stage and ignition coil configurations
The control unit. power s tage and ignition coil configuration may take one of four different forms .
As a general rule , the con tro l unit delivers ignition pulses to the power stage (which co ntrols the current in the pri .
mary w in ding of the igni tion coil) in response to signals from the various sensors and pick-ups. A high · tension volt-
age is induced in the secondary and fed to the distributor, wh ich delivers it to the appropriate spark plug, generating
aspark across the eleClrodes and igniting the fuel /air mixture.
A.The control unit , power stage and ignition coil may all be separate components. This app lies to EZ-Ksyst ems.
B.The con trol unit and power stage may be combi ned in a single unit. with aseparate ignition coil. This applies to
TZ· 28H .
C.The power stage and ignition coil may be com b ined, with the con trol unit separate. This applies to Rex-I.
O.
The control un it, power stage and ignition coil may compr ise a single unit .
• Alth ough the TZ-28H 'control u nit' does inco rpo rate a number of Ci r CUits additional to those used in EZ -K power s lages ,i ls pr i-
mary funct ion is closer 10 thaI of a power stage. and the term 'con lr ol Unit' is somewhat misleading.
16

Group 28 Igni t ion systems
Design and function - Components
Power stage and ignition coil
Function of power stage
The power stage (1) functions as an electronic switch controlling the current in the ignition coil on command from
the control unit (31. (The illustration shows the components of an EZ -K system. In the Renix-F system, the power
stage is integral with the control unit, although the principle of operation is the same .I
The function of the power stage is analogous to that of the points in a mechanica l ignition system, in that it alternate-
ly opens and closes the coil primary ground connection. Each time a cylinder fires, the power stage interrupts the
current in the primary , inducing a high-tension vol tage in the secondary.
Control signal
Once the control unit has computed a timing se tt ing, based on the signals from the various sensors, th e value is con-
verted
into a control signal for the power stage. When this signal goes high (+5 VI, the power stage permi ts the igni-
tion coil to charge. When the signal again falls (10 0Vl, the power stage interrupts the current in the ignition coil pri -
mary and the stored energy is released in the form of a high-tension pulse in the secondary.
Constant charge
In the EZ-K and TZ-28H systems , the power stage incorporates a circuit which continuously monitors the primary
cu rrent used to charge the igni tion coil and ensures that the charging current remains cons tant ,regardless of engine
speed or battery voltage. This feature is designed to ensure that the ignition coil (2) receives a constant charge at all
times ,irrespective of these parameters. As aresult, the charge in the coil is always a maximum and the ignition volt-
age remains constan t ly high.
Standing current protection
To avoid overheating of the ignition coil if the ignition is swi tched on with the engine atrest, the control unit in -
corporates a circuit which operates the standing current protection function via the power stage. Since the control
unit no longer receives signals from t he Hall generator or speed pick-up (whichever is applicablel when the eng i ne
has been stopped , it commands the power stage to interrupt the current in the primary winding of the coil.
Power stage cooling
Since operation of the power stage generates heat, the unit is mounted on aheat sink attached to the body. Secure
contact
between the unit and heat sink is essential to ensure that the working temperature is maintained wi thin ac-
ce pt able l imi t s. The heat is generat ed by the power circuit which ac ts as the 'wo rk ing' sec tion of the power stage,
making the 'control' circuits vulnerable to destruction. In systems in which the power stage is integral with the con -
trol
unit, the former is mounted on the inside of the control unit frame to ensure adequate cooling.
Ignition coil
The primary winding of the ignition coil in an electronic ignition system ( wh i ch generates extremely high voltages
up to a co ntinuou s 30 kV compared with an average of 15-18 kV in a conventional coil) has a relatively low resist-
ance.
Consequently , coils of this type are fitted with a plug (4) which opens to relieve the pressure in the unit in the
event of over heat ing and prevent deformation . NOTE : The plug muat be fi tted with a protective cap in the case ofacoil
ins
talled vertically in the engine compartment.
17

Group 28 Ign ition sys tem s
D
esign and funct ion - Components
2
1
REX-I
General
Since itis not technically pract ic al to use the control unit to regulate the relatively hi gh current in the ignition coil pri·
mary , this function is performed by a power stage wh ich employs control signals from the control unit to vary both
the charging time of the coil and the instant at which it delivers its high- tens ion pulse. The power stage opens and
closes the primary circuit ,in du cin ga high - tension voltage in the secondary each time the primary cu rrent is in-
terru pted.
Construction
The p ower stage (1) and igni tion coil (2) are assembled by means of screws (enabling t he units to be r ep laced indi -
vidually) . The power stage receives control signa ls from the control unit(g re en lead) across th e two - pole centre con -
nector (3) ( which is also used to ground the signal). The thr ee-pole co nnector ( 4) on the right supp lies the power
stage and igni t ion coil wilh battery voltage, grounds the coil and supplies the rev counter with asignal. The connec-
tor (5) on the left is not used .
The power s tage (1)i ncorporates the electrical circui ts which control the primary current in the ignition coil. Mount -
ed
on a bracket in the eng ine compartment, the power stagelignition coil assembly is provided with a large contac t
area
with the suspens ion strut hous ing to ensure that the heat generated is diSSipated.
The
ignition coil (2) is of the conv ent ion al type wi th a pr i mary and secondary wir ing. The high-tension induced in the
secondary is fed to the distributor from t erminal (6). As on most modern igni t ion systems , the HT voltage is of the
order of 30 kV .
Standing current protection
A functi on known as 's tand ing curren tprote ction' is provided 10 preventoverhea ti ng of th e igni t ion coil when the ig-
nition is s witch edon with the en gine atrest. When the engine is st opped, the control unit receives no speed signals
-and deliversa 'low' cont rol signal to the power stage, whi ch responds by opening the p rimary circui t of the coil.
18