1991 LEXUS SC400 oxygen sensor

SERVICE SPECIFICATIONS
SPECIFICATIONS
VSV (For EVAP) Resistance30±34

VSV (For EGR)Resistance33±39

TORQUE SPECIFICATIONS
Part tightenedN mkgf cmftVlbf
VSV for EGR X Intake manifold18185 13
EGR valve X Intake manifold18185 13
EGR valve X EGR Pipe64650 47
Catalytic converter (Front) X Exhaust manifold62630 46
Catalytic converter (Front) X Front Exhaust pipe43440 32
Front exhaust pipe X Center exhaust pipe43440 32
Sub±oxygen sensor X Front exhaust pipe1818013
EC±20±
EMISSION CONTROL SYSTEMS Service Specifications
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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
±
EMISSION CONTROL SYSTEMS Three±Way Catalyst (TWC) SystemEC±29
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SERVICE SPECIFICATIONS
SERVICE DATA
VSVResistance30±34

for EVAP
VSVResistance33±39

for EGR
EGR valveResistance19.9±23.4

(CALIF. only)
TORQUE SPECIFICATIONS
Part tightenedNVmkgf Vcmft Vlbf
VSV for EGR X Air intake chamber (Exc. USA Spec.)1818513
EGR valve X Air intake chamber18185 13
Catalytic converter (Main) X Exhaust manifold62630 46
Catalytic converter (Main) X Front exhaust pipe43440 32
Front exhaust pipe support bracket X Transmission43440 32
Front exhaust pipe X Center exhaust pipe43440 32
Main oxygen sensor X Front exhaust pipe4445033
EC±30±
EMISSION CONTROL SYSTEMS Servuce Specifications
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(Rear Catalytic Converter)
1. (USA Spec.)REMOVE SUB±OXYGEN SENSOR
Remove the two nuts and sub±oxygen sensor from the front
exhaust pipe.
2. REMOVE REAR CATALYTIC CONVERTER (FRONT EXHAUST PIPE)
(a) Remove the two bolts and nuts holding the front exhaust
pipe to the center exhaust pipe.
(b) Remove the two bolts and nuts holding the front exhaust
pipe to the front catalytic converter, and remove the front
exhaust pipe and two gaskets.
3. REINSTALL REAR CATALYTIC CONVERTER (FRONT EXHAUST PIPE)
Install the two new gaskets, the front exhaust pipe with the
four bolts and new nuts.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
4. (USA Spec.)
REINSTALL SUB±OXYGEN SENSOR
Install the new gasket, the sub±oxygen sensor to the front ex-
haust pipe with the two nuts.
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
±
EMISSION CONTROL SYSTEMS Three±way Catalyst (TWC) SystemEC±19
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\
 \

Front suspension crossmember x Engine mounting insulator  59 600 43
\
 \
PS pump x Cylinder head for bolt 39 400 29
\
 \
 for nut 43 440 32
\
 \
Propeller shaft x Transmission  79 805 58\
 \

Propeller shaft x Differential
  
79
 
805
 
58\
 \

Propeller shaft x Body
  
37
 
375
 
27\
 \
Center floor crossmember brace x Body  13 130 9\
 \
Fuel inlet hose x Fuel tube  30 310 22\
 \
TWC (Front) x Exhaust manifold  62 530 46\
 \
Front exhaust pipe x TWC (Front)  43 440 32\
 \
Front exhaust pipe support bracket x Transmission  43 440 32\
 \
Front exhaust pipe x Center Exhaust pipe  43 440 32\
 \
Center exhaust pipe x Tailpipe  44 195 14
\
 \
Main heated oxygen Exhaust manifold  44 450 33
\
 \
Sub heated oxygen sensor x Front exhaust pipe  44 450 33
±
1UZ ± FE ENGINE ENGINE MECHANICALEG±211
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Troubleshooting
If the CO/HC concentration does not comply with regulations,
perform troubleshooting in the order given below.
(a) Check main heated oxygen sensor operation.
(See MFI System on page EG±400)
(b) See the table below for possible causes, and then inspect and correct the applicable causes if necessary.
 CO HC Problems\
 \
Causes
 Normal High Rough idle\
 \
1. Faulty ignitions: 


 


 


\
 

\

Incorrect timing
   \
 \
Fouled, shorted or improperly gapped plugs
   \
 \
Open or crossed high±tension cords
   \
 \
Cracked distributor cap
   \
 \
2. Incorrect valve clearance   \
 \
3. Leaky EGR valve 


 


 


\
 

\
4. Leaky intake and exhaust valves
   \
 \
5. Leaky cylinder
 Low High Rough idle\
 \
1. Vacuum leaks:
   (Fluctuating HC reading)\
 \

PCV hose
   \
 \
EGR valve 


 


 


\
 

\

Intake manifold
   \
 \
Throttle body
   \
 \
IAC valve
   \
 \
Brake booster line
   \
 \
2. Lean mixture causing misfire 

High 

High 

Rough idle\
 

\
1. Restricted air filter
   (Black smoke from exhaust)\
 \
2. Faulty MFI systems:
   \
 \

Faulty pressure regulator
   \
 \
Clogged fuel return line
   \
 \
Defective ECT switch   \
 \
Faulty ECM 


 


 


\
 

\

Faulty injector
   \
 \
Faulty throttle position sensor
   \
 \
Faulty volume air flow meter
V02130
EG±36±
1UZ±FE ENGINE ENGINE MECHANICAL
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40. DISCONNECT MAIN HEATED OXYGEN SENSORCONNECTORS
Disconnect the RH and LH oxygen sensor connectors.
41. REMOVE CYLINDER HEADS
(a) Uniformly loosen the ten cylinder head bolts one side of each
cylinder head in several passes, in the sequence shown,
then do the other side as shown. Remove the 20 cylinder
head bolts and plate washers.
NOTICE:
w Cylinder head warpage or cracking could result from
removing bolts in incorrect order.
w Do not drop the plate washer for cylinder head bolt into
portion A of the cylinder head. If dropped into portion A,
the plate washer will pass through the cylinder head and
cylinder block into the oil pan.
±
1UZ±FE ENGINE ENGINE MECHANICALEG±91
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(b) Lift the cylinder head from the dowels on the cylinder block,and place the 2 cylinder heads on wooden blocks on a bench.
HINT: If the cylinder head is off, pry between the cylinder
head and cylinder block with a screwdriver.
NOTICE: Be careful not to damage the contact surfaces of the
cylinder head and cylinder block.
42. REMOVE EXHAUST MANIFOLD FROM RH CYLINDERHEAD
(a) Remove the 3 bolts and heat insulator.
(b) Remove the main heated oxygen sensor.
(c) Remove the 8 nuts, exhaust manifold and gasket.
43. REMOVE EXHAUST MANIFOLD FROM LH CYLINDER
HEAD
(a) Remove the 3 bolts and heat insulator.
EG±92
±
1UZ±FE ENGINE ENGINE MECHANICAL
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