The Control Unit Microprocessor Receives; Emergency Program; The Control Unit Microprocessor - Volvo 240 1989 Service Manual

Design and function
Fuel system LH2.4 - 240
The control unit microprocessor
receives:
Exhaust gas oxygen content information from the
Lambda-sand.
Rpm and crankshaft position information from the
ignition system control unit.
If
this information is
not forthcoming, the fuel system control unit will
not function.
Engine temperature information from the coolant
temperature sensor.
Engine load information from the air mass meter.
Information from the shutter switch as to whether
the throttle shutter is closed or wide open.
Electrical system voltage from the battery current.
The signal from the AC switch inform s if it is on,
and the signal from the compressor connection
indicates that the compressor is operating.
Emergency program
There is a "limp home" function provided if the signal
from the air mass meter ceases for some reas on,
such as the hot wi re burning off. A pre-programmed
value is used fo r Injection duration, allowing the
vehicle to be driven slowly to the garage.
The control unit microprocessor:
Sets the voltage of Ihe system by grounding the
system relay.
Breaks the sys tem relay ground if engine turns
ovartoo slo wly (engine has stopped). This keeps
the battery trom being drained and cuts off fuel
fl ow fro m the fuel pump when the engine isn't in
operation.
Grounds Ihe injectors, which regulates opening,
liming and injection duration.
Control s air valve tor constant idle speed (CIS).
Is connected to the diagnostic un it and provides
fault information about the various functions.
Provides the ignition system control unit with load
intormation .
Protects against too high rpm by shutting oH fuel
injection until the engine has stowed down.
USA/Canada: governs CH ECK ENG INE warning
lamps and shift indicator lamp.
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