LEXUS SC400 1991 Service Repair Manual

SYSTEM CIRCUIT
OPERATION
To maintain the most appropriate ignition timing, the ECU sends a control \
signal so that the igniter sends
current to the ignition coil and the spark plugs produce a spark. IG±4
±
IGNITION SYSTEM System Circuit, Operation
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PREPARATION
SST (SPECIAL SERVICE TOOLS)
RECOMMENDED TOOLS
EQUIPMENT
Part NameNote
Engine tune±up testerIgnition timing
Megger (Insulation resistance meter)Spark plug
Spark plug cleaner
Torque wrench
16 mm plug wrench
±
IGNITION SYSTEM PreparationIG±5
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ON±VEHICLE INSPECTION
SPARK TEST
CHECK THAT SPARK OCCURS(a) Remove the No.3 timing belt covers.(See steps 2 to 8 on pages IG±11 to 13)
(b) Disconnect the high±tension cords (from the ignition
coils) from the distributor caps.
(c) Hold the end about 12.5 mm (0.50 in.) from the body ground.
(d) Check if spark occurs while engine is being cranked.
HINT: To prevent gasoline from being injected from injectors
during this test, crank the engine for no more than 1±2 se-
conds at a time.
If the spark does not occur, perform the test as follows:
(e) Reconnect the high±tension cords to the distributor caps.
(f) Reinstall the No.3 timing belt covers. (See steps 5 to 11 on pages IG±17 to 19)
IG±6
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IGNITION SYSTEM On±Vehicle Inspection
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INSPECTION OF HIGH±TENSION CORDS
1. REMOVE HIGH±TENSION CORDS(See steps 1 to 9 on pages IG±11 to 14)
2. INSPECT HIGH±TENSION CORD RESISTANCE
Using an ohmmeter, measure the resistance.
Maximum resistance: 25 k
per cord
If the resistance is greater than maximum, replace the high±
tension cord.
3. REINSTALL HIGH±TENSION CORDS (See steps 4 to 13 on pages IG±11 to 19)
INSPECTION OF SPARK PLUGS
NOTICE:
wNever use a wire brush for cleaning.
w Never attempt to adjust the electrode gap on used spark
plug.
w Spark plug should be replaced every 100,000 km (60,000
miles).
1. DISCONNECT HIGH±TENSION CORDS FROM SPARK
PLUGS (See steps 1 to 9 on pages IG±11 to 13)
2. INSPECT ELECTRODE
Using a megger (insulation resistance meter), measure the
insulation resistance.
Correct insulation resistance: 10 M
or more
If the resistance is less than specified, proceed to step 4.
HINT: If a megger is not available, the following simple meth-
od of inspection provides fairy accurate results.
(Simple Method)
(a) Quickly race the engine to 4,000 rpm five times.
(b) Remove the spark plug. (See step 3)
(c) Visually check the spark plug.
If the electrode is dry. . . . . Okay
If the electrode is wet . . . . . Proceed to step 4
(d) Reinstall the spark plug.
(See step 7 on page IG±8)
3. REMOVE SPARK PLUGS Using a 16 mm plug wrench, remove the spark plugs.
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IGNITION SYSTEM On±Vehicle InspectionIG±7
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4. VISUALLY INSPECT SPARK PLUGSCheck the spark plug for thread damage and insulator dam-
age.
If abnormal, replace the spark plug.
Recommended spark plug: ND PK20R11
NGK BKR6EP11
5. INSPECT ELECTRODE GAP
Maximum electrode gap: 1.3 mm (0.051 in.)
If the gap is greater than maximum, replace the spark plug.
Correct electrode gap of new spark plug:1.1 mm (0.043 in.)
NOTICE: If adjusting the gap of a new spark plug, bent
only the base of the ground electrode. Do not touch the
tip. Never attempt to adjust the gap on the used plug.
6. CLEAN SPARK PLUGS If the electrode has traces of wet carbon, allow it to dry and
then clean with a spark plug cleaner.
Air pressure: Below 588 kPa (6 kgf/cm2, 85 psi)
Duration: 20 seconds or less
HINT: If there are traces of oil, remove it with gasoline before
using the spark plug cleaner.
7. REINSTALL SPARK PLUGS Using a 16 mm plug wrench, install the spark plug.
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
8. RECONNECT HIGH±TENSION CORDS TO SPARK
PLUGS
(See steps 4 to 13 on pages IG±16 to 19)
IG±8
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IGNITION SYSTEM On±Vehicle Inspection
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INSPECTION OF IGNITION COIL
1. (RH IGNITION COIL)REMOVE IGNITION COIL (See page IG±21)
2. (LH IGNITION COIL)
DISCONNECT IGNITION COIL CONNECTOR AND HIGH±
TENSION CORD FROM IGNITION COIL
3. INSPECT PRIMARY COIL RESISTANCE Using an ohmmeter, measure the resistance between posi-
tive (+) and negative (±) terminals.
Primary coil resistance (Cold): 0.40±0.50

If the resistance is not as specified, replace the ignition coil.
4. INSPECT SECONDARY COIL RESISTANCE Using an ohmmeter, measure the resistance between posi-
tive (+) and high±tension terminals.
Secondary coil resistance (Cold): 10.0±14.0 k

If the resistance is not as specified, replace the ignition coil.
5. (RH IGNITION COIL) REINSTALL IGNITION COIL (See page IG±22)
6. (LH IGNITION COIL) RECONNECT IGNITION COIL CONNECTOR AND HIGH±
TENSION CORD FROM IGNITION COIL
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IGNITION SYSTEM On±Vehicle InspectionIG±9
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INSPECTION OF CAM POSITION
SENSORS
1. DISCONNECT CAM POSITION SENSOR CONNECTORS(a) (RH Cam Position Sensor)Disconnect the cam position sensor connector from the
ignition coil bracket.
(See steps 5 (a) on page IG±24)
(b) Disconnect the cam position sensor connectors.
2. INSPECT CAM POSITION SENSOR RESISTANCE Using an ohmmeter, measure the resistance between termi-
nals.
Resistance (Cold):
835±1,350
at ±10± +40 5C (14±104 5F)
If the resistance is not as specified, replace the cam position
sensor.
3. RECONNECT CAM POSITION SENSOR CONNECTORS
INSPECTION OF ENGINE SPEED
SENSOR
1. REMOVE ENGINE SPEED SENSOR (See page IG±30)
2. INSPECT ENGINE SPEED SENSOR RESISTANCE Using an ohmmeter, measure the resistance between termi-
nals.
Resistance (Cold):
835±1,350
at ±10± +40 5C (14±104 5F)
If the resistance is not as specified, replace the engine speed
sensor.
3. REINSTALL ENGINE SPEED SENSOR (See page IG±30)
INSPECTION OF ENGINE SPEED
SENSOR
(See procedure Spark Test on page IG±6)
IG±10
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IGNITION SYSTEM On±Vehicle Inspection
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HIGH±TENSION CORDS AND CORD
CLAMPS
COMPONENTS FOR REMOVAL AND
INSTALLATION
REMOVAL OF HIGH±TENSION CORDS
1. DISCONNECT CABLE FROM NEGATIVE TERMINAL OFBATTERY
CAUTION: Work must be started after approx. 20 se-
conds or longer from the time the ignition switch is
turned to the ºLOCKº position and the negative (±) termi-
nal cable is disconnected from the battery.
±
IGNITION SYSTEM High±Tension Cords and Cord ClampsIG±11
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2. REMOVE INTAKE AIR CONNECTOR(a) Disconnect the following hoses:(1) Air hose from ISC valve
(2) Air hose (from PS air control valve) from intake air connector
(b) Remove the bolt holding the intake air connector to the cylinder head cover.
(c) Loosen the two hose clamps.
(d) Disconnect the intake air connector from the throttle
body and air cleaner hose, and remove the throttle body.
3. REMOVE UPPER HIGH±TENSION CORD COVER (a) Remove the two mounting bolts.
(b) Disconnect the front side claw groove of the cord coverfrom the claw of the lower cover, and remove the cord
cover.
4. REMOVE RH ENGINE WIRE COVER Remove the bolt and engine wire cover.
5. REMOVE LH ENGINE WIRE COVER Remove the two bolts and engine wire cover.
IG±12
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IGNITION SYSTEM High±Tension Cords and Cord Clamps
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6. REMOVE VSV FOR EVAP SYSTEMRemove the two bolts, and disconnect the VSV from cylinder
head and timing belt cover.
7. REMOVE RH NO.3 TIMING BELT COVER Remove the three bolts and timing belt cover.
8. REMOVE LH NO.3 TIMING BELT COVER (a) Remove the four mounting bolts.
(b) Disconnect the cord grommet from the timing belt cover,
and remove the timing belt cover.
(c) Remove the cord grommet from the high±tension cord.
9. REMOVE HIGH±TENSION CORDS (a) Disconnect the high±tension cords from the spark plugs
and distributor caps. Disconnect the high±tension cords
at the rubber boot. Do not pull on the cords.
NOTICE: Pulling on or bending the cords may damage
the conductor inside.
±
IGNITION SYSTEM High±Tension Cords and Cord ClampsIG±13
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