LEXUS SC400 1991 Service Repair Manual

(b) Apply battery voltage across the terminals.
(c) Check that the air flows from port E to the filter.
If operation is not as specified, replace the VSV.
4. REINSTALL VSV (a) Install the VSV with the bolt.
Torque: 18 N Vm (185 kgf Vcm, 13 ft Vlbf)
(b) Connect the following hoses:
(1) Vacuum hose (from EGR valve) to VSV
(2) Vacuum hose (from EGR vacuum modulator) to VSV
(c) Connect the VSV connector.
5. RECONNECT CABLE TO NEGATIVE TERMINAL OF BATTERY
INSPECTION OF EGR VACUUM
MODULATOR (Exc. USA Spec.)
1. DISCONNECT VACUUM HOSES FROM EGR VACUUMMODULATOR
Disconnect the three vacuum hoses from ports P, Q and R of
the EGR vacuum modulator.
2. INSPECT EGR VACUUM MODULATOR OPERATION (a) Block ports P and R with your finger.
(b) Blow air into port Q, and check that the air passesthrough to the air filter side freely.
(c) Start the engine, and maintain speed at 2,500 rpm.
(d) Repeat the above test. Check that there is a strong resistance to air flow.
3. RECONNECT VACUUM HOSES TO EGR VACUUM MODULATOR
Connect the three vacuum hoses to the proper locations.
EC±20
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) System
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COMPONENTS FOR REMOVAL AND INSTALLATION OF EGR VALVE
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±21
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INSPECTION OF EGR VALVE
(USA Spec.)
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.
2. DISCONNECT EGR VALVE CONNECTOR
3. INSPECT EGR VALVE RESISTANCE Using an ohmmeter, measure the resistance between termi-
nal B1 (or B2) and other terminals (S1, S2, S3 and S4).
Resistance (Cold): 19.9±23.4

4. DRAIN ENGINE COOLANT (See page CO±6)
5. REMOVE EGR VALVE (a) Disconnect the following hoses:(1) Water by±pass hose (from ISC valve) from the EGR
valve
(2) Water by±pass hose (from rear water by±pass joint) from the EGR valve
(b) Remove the two nuts, EGR valve and gasket.
6. INSPECT EGR VALVE
A. Visually inspect EGR valve Check for sticking and heavy carbon deposits.
If a problem is found, replace the EGR valve assembly.
EC±22
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) System
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B. Inspect EGR valve operation(a) Remove the three bolts and stepping motor from thehousing.
(b) Apply battery voltage to terminal B1 (or B2), and while repeately grounding (*S4)±(S4 and *S3)±(S3 and
*S2)±(S2 and *S1)±(S1 and *S4) in sequence, check
that the valve moves toward the open position.
HINT: Keep the terminal marked with an asterisk (*) grounded
while proceeding to the next grounding.
(c) Apply battery voltage to terminal B1 (or B2), and while repeately grounding (*S1)±(S1 and *S2)±(S2 and
*S3)±(S3 and *S4)±(S4 and *S1) in sequence, check
that the valve moves toward the closed position.
HINT:
w Keep the terminal marked with an asterisk (*) grounded
while proceeding to the next grounding.
w Perform this operation after opening the valve by
performing step (b) above.
If operation is not as specified, replace the EGR valve assem-
bly.
(d) Reinstall the stepping motor to the housing with the three bolts.
7. REINSTALL EGR VALVE (a) Place a new gasket on the EGR valve adaptor.
NOTICE:
w Do not touch the adaptor and EGR valve surfaces of the
gasket with your hand.
w Align the port holes of the gasket and adaptor. Be careful
of the installation direction.
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±23
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(b) Install the EGR valve with the two nuts.
Torque: 18 NVm (185 kgf Vcm, 13 ft Vlbf)
(c) Connect the following hoses:
(1) Water by±pass hose (from ISC valve) to the EGR valve
(2) Water by±pass hose (from rear water by±pass joint) to the EGR valve
8. RECONNECT EGR VALVE CONNECTOR
9. RECONNECT CABLE TO NEGATIVE TERMINAL OF BATTERY
10. REFILL WITH ENGINE COOLANT (See page CO±7)
INSPECTION OF EGR VALVE
(Exc. USA Spec.)
1. DRAIN ENGINE COOLANT (See page CO±6)
2. REMOVE EGR VALVE (a) Disconnect the following hoses:(1) Vacuum hose (from VSV) from EGR valve
(2) Vacuum hose (from VSV) from EGR vacuum
modulator
(3) Vacuum hose (from EGR vacuum modulator) f rom EGR valve
(4) Water by±pass hose (from ISC valve) from the
EGR valve
(5) Water by±pass hose (from rear water by±pass joint) from the EGR valve
(b) Disconnect the vacuum modulator bracket from the
EGR valve.
(c) Remove the two nuts, EGR valve and gasket.
EC±24
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) System
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3. INSPECT EGR VALVECheck for sticking and heavy carbon deposits.
If a problem is found, replace the EGR valve assembly.
4. REINSTALL EGR VALVE (a) Place a new gasket on the EGR valve adaptor.
NOTICE:
w Do not touch the adaptor and EGR valve surfaces of the
gasket with your hand.
w Align the port holes of the gasket and adaptor.
Be careful of the installation direction.
(b) Install the EGR valve with the two nuts.
Torque: 18 N Vm (185 kgf Vcm, 13 ft Vlbf)
(c) Install the vacuum modulator bracket to the EGR valve.
(d) Connect the following hoses:
(1) Vacuum hose (from VSV) to EGR valve
(2) Vacuum hose (from VSV) to EGR vacuum modula- tor
(3) Vacuum hose (from EGR vacuum modulator) to EGR valve
(4) Water by±pass hose (from ISC valve) to the EGR
valve
(5) Water by±pass hose (from rear water by±pass joint) to the EGR valve
5. REFILL WITH ENGINE COOLANT (See page CO±7)
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±25
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THREE±WAY CATALYST (TWC) SYSTEM
DESCRIPTION
To reduce HC, CO and NOx emissions, they are oxidized, reduced and convert\
ed to nitrogen (N2), carbon
dioxide (CO2) and water (H2O) by the catalyst.
OPERATION
EC±26±
EMISSION CONTROL SYSTEMS Three±Way Catalyst (TWC) System
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INSPECTION OF EXHAUST PIPE
ASSEMBLY
1. CHECK CONNECTIONS FOR LOOSENESS OR DAMAGE
2. CHECK CLAMPS FOR WEAKNESS, CRACKS OR
DAMAGE
INSPECTION OF CATALYTIC
CONVERTERS
CHECK FOR DENTS OR DAMAGE If any part of protector is damaged or dented to the extent that
it contacts the converter, repair or replace it.
INSPECTION OF HEAT INSULATORS
1. CHECK HEAT INSULATOR FOR DAMAGE
2. CHECK FOR ADEQUATE CLEARANCE BETWEEN
CATALYTIC CONVERTER AND HEAT INSULATOR
COMPONENTS FOR REPLACEMENT OF CATALYTIC CONVERTERS
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EMISSION CONTROL SYSTEMS Three±Way Catalyst (TWC) SystemEC±27
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COMPONENTS FOR REPLACEMENT OF CATALYTIC CONVERTERS (Cont'd)
REPLACEMENT OF CATALYTIC
CONVERTERS
(Main Catalytic Converters)
1. REMOVE CATALYTIC CONVERTERS (MAIN)
(a) Check that the converter is cool.
(b) Remove the four bolts holding the pipe support bracket to thetransmission.
(c) Remove the four bolt and nuts holding the catalytic converters
to the front exhaust pipe. Remove the support bracket.
(d) Disconnect the front exhaust pipe from the catalytic converter,
and remove the two gaskets.
(e) Remove the three nuts, converter and gasket. remove the two
catalytic converters.
2. REINSTALL MAIN CATALYTIC CONVERTER
(a) Install a new gasket and the catalytic converter to the exhaust manifold with three new nuts. Install the two catalytic
converters.
Torque: 62 N Vm (630 kgf Vcm, 46 ft Vlbf)
(b) Install a new gasket to each front end of the front exhaust pipe,
and temporarily connect the front exhaust pipe to the catalytic
converters.
(c) Temporarily install the pipe support bracket to the transmission with the four bolts.
(d) Connect the front exhaust pipe to the catalytic converter with the four bolts and new nuts.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
(e) Tighten the four bolts holding the pipe support bracket to the transmission.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
EC±28±
EMISSION CONTROL SYSTEMS Three±Way Catalyst (TWC) System
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(Sub±Catalytic Converter (USA Spec.
only)
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.
2. DISCONNECT SUB±OXYGEN SENSOR CONNECTORS Disconnect the grommet from the floor, and disconnect the
sub±oxygen sensor from the front exhaust pipe.
3. REMOVE FRONT EXHAUST PIPE (SUB±CATALYTIC CONVERTER)
(a) Remove the four bolts holding the front exhaust pipe tothe transmission.
(b) Remove the two bolts and nuts holding the front exhaust
pipe to the center exhaust pipe.
(c) Remove the four bolts and nuts holding the front pipe to the catalytic converter, and remove the pipe support
bracket, front pipe and three gaskets.
4. REINSTALL FRONT EXHAUST PIPE (SUB±CATALYTIC CONVERTER)
(a) Temporarily install the pipe support bracket to thetransmission with the four bolts.
(b) Install three new gaskets, the front exhaust pipe and pipe support bracket with the six bolts and new nuts.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
(c) Tighten the four bolts holding the pipe support bracket
to the transmission.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
5. RECONNECT SUB±OXYGEN SENSOR CONNECTORS
(a) Install the two sub±oxygen sensors to the front exhaustpipe.
Torque: 44 N Vm (450 kgf Vcm, 33 ft Vlbf)
HINT:
w Before installing the s ub±oxygen sensor, twist the
sensor wire counterclockwise 3 \frb\1/2\fre turns.
w After installing the sub±oxygen sensor, check that the
sensor wire is not twisted. If it is twisted, remove the
sub±oxygen sensor and reinstall it.
(b) Install the two wire grommets to the floor.
6. RECONNECT CABLE TO NEGATIVE TERMINAL OF
BATTERY
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EMISSION CONTROL SYSTEMS Three±Way Catalyst (TWC) SystemEC±29
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