Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 107

ESA - Functions of Engine EC U
AIR-FUEL RATIO FEEDBACK CORRECTION
(engines with oxygen sensor )
During air-fuel ratio feedback correction, the
engine speed varies according to the increase or
decrease in the fuel injection volume . The
engine is especially sensitive to changes in the
air-fuel ratio when it is idling, so stable idling is
ensured by advancing the ignition timing at this
time in order to match the fuel injection volume
of air-fuel ratio feedback correction .
The ignition timing angle is advanced a
maximum of approximately 5° by this correction .
This correction is not executed while the vehicle
is being driven .
-RELEVANT SIGNALS
• Oxygen sensor (OX)
• Thro tt le position (IDL)
• Vehicle speed (SPD)
KNOCKING CORRECTION
a
If engine knocking occurs, the knock sensor
converts the vibrations created by the knocking
into voltage signals and sends them to the
Engine ECU .
Distributo r
Spark plug
Igniter & coi l
Sensor
Engine EC U
w
Engine knocking
correctio n circuitry
OHP 6 7
The ECU judges whether the strength of the
knocking is at one of three levels, strong,
medium or weak, according to the strength of
the KNK signals, and changes the corrective
ignition retard angle accordingly . In other words,
if the knocking is strong, the ignition timing is
retarded a lot, while if knocking is Weak, it is
retarded only a li tt le .
When engine knocking stops, the ECU stops
retarding and begins advancing the ignition
timing by fixed angles a li tt le at a time .
This ignition timing advance continues until
engine knocking recurs, at which point the
ignition timing is again retarded .
The ignition timing angle is retarded a maximum
of approximately 10° by this correction .
Retarding of the ignition timing during knocking
is carried out within the knocking correction
range . In some engines, this means when the
engine is operating under a heavy load (vacuum
below approx . 26 .7 kPa [200 mmHg, 7 .9 in .Hg]),
while in other engines, it covers vi rt ually the full
engine load range .
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