Volvo 819 E - Design and Function

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 d service 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 icant factors 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 to a minimum . As a result, Volvo has, in recent years, co mp letely replaced its r 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 a series 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 ts are 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 its 700 series models, in terms of design
and function , as well as fault tracing, repair and maintenance. The fir st part 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 are in-
cluded.
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