Control Unit; Seof-Adjusting Functions; Self-Adjusting Idle Speed Regulation; Self-Adjusting Lambda-Song - Volvo 240 1989 Service Manual

Design and function
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Ignition
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rela'y
Fuel system L H2.4 - 240
Control unit
The control unit has a microproce ssor that receives
s ignal s fro m the various sensors regarding
operational conditions, evaluates them in relation to
pre-programmed valuas and calculates the correct
injector opening durations (in mil/i-seconds per revo­
lution) .
The conlrol unit govern s idling rpm by regulating the
amount of aIr by-passing th e throttle valve. It also
controls other functions, such as the cold start valve,
the fuel pump and the rel ay. O ne important function
is monitoring fault fracing via th e diagnostic socket.
Self-adjusting functions
The control unit is adaptive in that it adjusts its calcu­
lations according to assimilated input.
Sell-adjusting Idle speed regu lation
In time, wear and coatings will affect the operation of
th e throHle valve, causing less aIr to enter the intake
system . Instead 01 w orking fro m a pre- programmed
value the idle valve receives a signal that is adapted
to the experiences which the control unit has learned
from previous driving periods .
Self-adjusting Lambda-sand
The Lambda-sond operates in a similar fas hion . It
senses if the fuel mixture is rich or lean and adjusts
the control unit's Lambda regulator accordingly.
The self-regulating mechanism keeps the control unit
function at midpoint. This does away with the need
to adjust the CO content and automatically compen­
sates for the effects of tolerances and wear in the in­
jection system.
Whenever th e vehicle is started and driven, the con­
trol unit will use the value that has been learned from
previous driving periods.
8