Hyundai Sonata 1991 Shop Manual page 263

MPI SYSTEM INSPECTION
MPI SYSTEM
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If the MPI system components (sensors, ECU, injector, etc.) fail,
interruption or failure to supply the proper amount of fuel for
various engine operating conditions will result. The following
situations can be encountered.
1. Engine is hard to start or does not start at all.
2. Unstable idle
3. Poor driveability
If any of the above conditions is noted, first perform an
inspection by self-diagnosis and subsequent basic engine checks
(ignition system malfunction, incorrect engine adjustment, etc.),
and then inspect the MPI system components with the multi-use
tester (MUT).
CAUTIONS
1) Before removing or installing any part, read the diagnosis
code and then disconnect the battery negative (-)
terminal.
2) Before disconnecting the cable from battery terminal. turn
the ignition switch to OFF. Removal or connection of bat-
tery cable during engine operation or while the ignition
switch is ON could cause inaccurate operation of the ECU
or damage to semiconductors.
3) The control harnesses between the ECU and oxygen sen-
sor are shielded wires with the shield grounded to the
body in order to prevent the influence of ignition noises
and radio interference. When the shielded wire is faulty the
control harness must be replaced.
Malfunction Indicator Light (Only U.S.A.)
Among the self-diagnosis items, a malfunction indicator light
comes on to notify the driver of the emission control items when
an irregularity is detected.
However, when an irregular signal returns to normal and the
engine control unit judges that it has returned to normal, the
malfunction indicator light goes out.
Moreover, when the ignition switch is turned off, the light goes
out. Even if the ignition switch is turned on again, the light does
not come on until the irregularity is detected.
Immediately after the ignition switch is turn on, the malfunction
indicator light is lit for 5 seconds to indicate that the malfunction
indicator light operates normally.
Item Indicated By The MIL
o Computer
o Oxygen sensor
o Air-flow sensor
o Intake air temperature sensor
o Throttle position sensor
31-38
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Malfunction indicator light
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