1991 LEXUS SC400 VSV

EXHAUST GAS RECIRCULATION (EGR) SYSTEM
DESCRIPTION
To reduce NOx emission, part of the exhaust gases are recirculated through\
the EGR valve to the intake man-
ifold to lower the maximum combustion temperature.
OPERATION
To reduce NOx emission, part of the exhaust gases are recirculated through\
the EGR valve to the intake manifold to lower the
maximum combustion temperature.
Coolant
Temp.VSVThrottle Valve OpeningPressure in the EGR Valve Pressure ChamberEGR VacuumModulatorEGR
ValveExhaust Gas
Below 45
COPENCLOSEDNot recircu-
(113
F)OPEN±±±CLOSEDlated
Positioned be-
low EGR port±±CLOSEDNot recircula- ted
Above 50 5C
(122 5F)CLOSEDPositioned be-
tween EGRport
(1)
LOW* Pressure constantly
alternating between
OPENS passage to atmosphereCLOSEDNot recircula- ted
tween EGR port
and R port(2)
HIGHalternating between
low and highOPENS passage
to atmosphereOPENRecirculated
Above 50 5C
(122 5F)CLOSEDPositioned
above R port(3)
HIGH**CLOSES passage to atmosphereOPENRecirculated(increase)
* Pressure increases Modulator closes EGR valve opens Pressure drops EGR Valve closes Modulator opens
** When the throttle valve is positioned above the R port, the EGR vacuum m\
odulator will close the atmosphere passage and
open the EGR valve to increase the EGR gas, even if the exhaust pressure\
is insufficiently low.
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±11
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(e) Check whether the engine rpm increases 100±300 rpmunder the following conditions:
Coolant temp.
Below 45 5C (113 5F) . . . NO increase
Above 50 5C (122 5F) . . . Increases
INSPECTION OF VSV
1. REMOVE VSV
(a) Disconnect the VSV connector.
(b) Disconnect the two vacuum hoses from VSV.
(c) Remove the bolt and VSV from the intake manifold.
2. INSPECT VSV (a) Inspect VSV for open circuit.Using an ohmmeter, check that there is continuity be-
tween the terminals.
Resistance (Cold): 33±39

If there is no continuity, replace the VSV.
(b) Inspect VSV for ground.
Using an ohmmeter, check that there is no continuity be-
tween each terminal and the body.
If there is continuity, replace the VSV.
(c) Inspect VSV operation: 1) Check that the air flows from ports E to G
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±13
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2) Apply battery voltage across the terminals
3) Check that the air flows from port E to port G
If operation is not as specified, replace the VSV.
3. REINSTALL VSV (a) Install the VSV with the nut.
Torque: 18 N Vm (185 kgf Vcm, 13 ft Vlbf)
(b) Connect the following hoses:
(1) Vacuum hose (from throttle body)
(2) Vacuum hose (from EGR vacuum modulator)
(c) Connect the VSV connector.
INSPECTION OF EGR VACUUM
MODULATOR
1. DISCONNECT VACUUM HOSES FROM EGR VACUUM MODULATOR
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 the 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±14
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) System
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INSPECTION OF VSV (Exc. 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. REMOVE VSV (a) Disconnect the VSV connector.
(b) Disconnect the following hoses:(1) Vacuum hose (from EGR valve) from VSV
(2) Vacuum hose (from EGR vacuum modulator) from VSV
(c) Remove the bolt and VSV.
3. INSPECT VSV
A. Inspect VSV for open circuit Using an ohmmeter, check that there is continuity between
the terminals.
Resistance (Cold): 33±39

If there is no continuity, replace the VSV.
B. Inspect VSV for ground Using an ohmmeter, check that there is no continuity be-
tween each terminal and the body.
If there is continuity, replace the VSV.
C. Inspect VSV operation (a) Check that the air flows from ports E to G.
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±19
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(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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(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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(b) Remove the bolt holding the intake air connector to thecylinder head cover.
(c) Remove the 2 hose clamps.
(d) Disconnect the intake air connector from the throttle body and air cleaner hose, and remove the intake air connector.
6. REMOVE UPPER HIGH±TENSION CORD COVER
(a) Remove the 2 bolts.
(b) Disconnect the front side claw groove of the upper cord cover
from the claw of lower cord cover, and remove the upper cord
cover.
7. REMOVE RH ENGINE WIRE COVER Remove the bolt and engine wire cover.
8. REMOVE LH ENGINE WIRE COVER Remove the 2 bolts and engine wire cover.
9. REMOVE VSV FOR EVAP SYSTEM Remove the 2 bolts, and disconnect the VSV from the cylin-
der head cover and timing belt cover.
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1UZ±FE ENGINE ENGINE MECHANICALEG±15
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