oxygen sensor LEXUS SC400 1991 Service User Guide

(b) Install the exhaust manifold with 8 new nuts. Uniformlytighten the nuts in several passes.
Torque: 44 N Vm (450 kgf Vcm, 33 ft Vlbf)
(c) Install the main heated oxygen sensor.
Torque: 44 N Vm (450 kgf Vcm, 33 ft Vlbf)
(d) Install the heat insulator with the 3 bolts.
3. INSTALL CYLINDER HEADS
A. Place cylinder head on cylinder block
(a) Place 2 new cylinder head gaskets in position on the cylinder
block.
HINT: On the rear side of the cylinder head gasket are
painted marks to distinguish the LH and RH banks, a white
painted mark for the RH bank and a yellow painted mark for
the LH bank.
NOTICE: Be careful of the installation direction.
(b) Place the 2 cylinder heads in position on the cylinder headgaskets.
EG±110
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(e) Retighten the cylinder head bolts 90
in the numerical order
shown.
(f) Check that the painted mark is now at a 90
angle to front.
4. CONNECT MAIN HEATED OXYGEN SENSOR CONNECTORS
Connect the RH and LH oxygen sensor connectors.
5. INSTALL CIRCULAR PLUGS
(a) Place 2 new circular plugs in position on the cylinder heads, facing the cup side forward.
(b) Remove any old packing (FIPG) material.
(c) Apply seal packing to the bearing caps as shown.
Seal packing: Part No. 08826±00080 or equivalent
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(i) Remove the bolt holding the engine wire clamp to the heaterwater valve bracket.
(j) Remove the 2 bolts holding the engine wire clamp to the
body.
(k) Pull out the engine wire from the cabin.
NOTICE: Be careful not to damage the engine wire.
28. DISCONNECT SUB HEATED OXYGEN SENSORS FROM FRONT EXHAUST PIPE
(a) Disconnect the 2 wire grommets from the floor panel.
(b) Disconnect the 2 oxygen sensors from the exhaust pipe.
29. REMOVE FRONT EXHAUST PIPE
(a) Remove the 4 bolts holding the pipe support bracket to the transmission.
(b) Remove the 2 bolts and nuts holding the front exhaust pipe to the center exhaust pipe.
(c) Remove the 4 bolts and nuts holding the front exhaust pipe to the TWC.
(d) Remove the pipe support bracket, front exhaust pipe and 3 gaskets.
30. REMOVE TWC (FRONT) Using a 14 mm deep socket wrench, remove the 3 nuts, TWC
and gasket. Remove the 2 TWC.
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7. INSTALL TAILPIPE
(a) Install the hook of the tailpipe to the ring on the tailpipebracket.
(b) Install a new gasket and tailpipe to the center exhaust pipe with 2 bolts. Install the 2 tailpipes.
Torque: 19 N Vm (195 kgf Vcm, 14 ft Vlbf)
8. INSTALL TWC (FRONT)
Using a 14 mm deep socket wrench, install a new gasket and
the TWC with 3 new nuts. Install the 2 TWC.
Torque: 62 N Vm (630 kgf Vcm, 46 ft Vlbf)
9. INSTALL FRONT EXHAUST PIPE
(a) Temporarily install the pipe support bracket with the 4 bolts.
(b) Temporarily install 3 new gaskets and the exhaust pipe with
the 6 bolts and nuts.
(c) Tighten the 4 bolts and nuts holding the TWC to the front exhaust pipe.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
(d) Tighten the 2 bolts and nuts holding the front exhaust pipe to
the center exhaust pipe.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
(e) Tighten the 4 bolts holding the pipe support bracket to the
transmission.
Torque: 43 N Vm (440 kgf Vcm, 32 ft Vlbf)
10. INSTALL SUB HEATED OXYGEN SENSORS
Install the 2 oxygen sensors to the front exhaust pipe.
Torque: 44 N Vm (450 kgf Vcm, 33 ft Vlbf)
HINT:
w Before installing the oxygen sensor, twist the sensor
wire counterclockwise 3 1/2 turns.
w After installing the oxygen sensor, check that the sensor
wire is not twisted. If it is twisted, remove the oxygen
sensor and reinstall it.
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(i) Remove the bolt holding the engine wire clamp to theheater water valve bracket.
(j) Remove the two bolts holding the engine wire clamp to the body.
(k) Pull out the engine wire from the cabin.
28. REMOVE FRONT EXHAUST PIPE (a) Disconnect the grommet from the floor, and disconnectthe sub±oxygen sensor from the exhaust pipe.
Disconnect the two sub±oxygen sensors.
(b) Remove the four bolts holding the front exhaust pipe to the transmission.
(c) Remove the two bolts and nuts holding the front exhaust
pipe to the center exhaust pipe.
(d) Re mo ve th e fo u r bo lts an d nu ts ho ld in g th e fro n t
exhaust pipe to the catalytic converter. Remove the pipe
support stay, front exhaust pipe and three gaskets.
29. REMOVE CATALYTIC CONVERTERS (MAIN) Remove the three nuts, catalytic converter and gasket. Re-
move the two catalytic converters.
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9. INSTALL CATALYTIC CONVERTERS (MAIN)Install a new gasket and the catalytic converter with three
new nuts. Install the two catalytic converters.
Torque: 62 N Vm (630 kgf Vcm, 46 ft Vlbf)
10. INSTALL FRONT EXHAUST PIPE
(a) Temporarily install the pipe support stay with the fourbolts.
(b) Install three new gaskets, the exhaust pipe and pipe support stay with the six bolts and 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)
(d) Install the two sub±oxygen sensors to the exhaust pipe.
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 1/2 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.
(e) Install the wire grommets to the floor.
11. CONNECT ENGINE WIRE TO CABIN (a) Push in the engine wire through the cowl panel.
(b) Install the engine wire clamp with the three bolts.
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Troubleshooting
If the CO/HC readings do not comply with regulations, pre-
form troubleshooting in the order given below.
(a) Check oxygen sensor operation.(See page FI±73)
(b) See the table below for possible cause, and then inspect
and correct the applicable causes if necessary.
 CO HC Symptoms Cause
 Normal High Rough idle 1. Faulty ignition:
     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 leak:
   (Fluctuating HC reading)  PCV hose
     EGR valve
     Intake manifold
     Air intake chamber
 Throttle body     ISC valve     Brake booster line    2 Lean mixture causing misfire High High Rough idle 1. Clogged air filter
   (Black smoke from exhaust) 2. Faulty EFI system
     Faulty pressure regulator
     Clogged fuel return line
     Defective engine coolant temp. sensor
     Defective intake air temp. sensor
     Faulty ECU
 Fault injectors     Faulty throttle position sensor     Faulty volume air flow meter
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ENGINE MECHANICAL Idle and/or 2,500 rpm CO/HC CheckEM±21
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Troubleshooting
If the HC/CO concentration does not comply with regulations,
perform troubleshooting in the order given below.
(a) Check oxygen sensor operation.(See page FI±113)
(b) See the table below for possible cause, and then inspect
and correct the applicable causes if necessary.
 

HC 

CO 

Symptoms\
 

\
Cause
 High Normal Rough idle\
 \
1. Faulty ignitions:
   \
 \

Incorrect timing
   \
 \

Fouled, shorted or improperly gapped plugs
   \
 \

Open or crossed high±tension cords
Ckddiib\

Cracked distributor cap
Ill   \
 \
2. Incorrect valve clearance
3 L k EGR l   \
 \
3. Leaky EGR valve
4L k i k d h l   \
 \
4. Leaky intake and exhaust valves
L k li d   \
 \
5. Leaky cylinders
 High Low Rough idle\
 \
1. Vacuum leaks:
   (Fluctuating HC reading)\
 \

PCV hoses
   \
 \

EGR valve
   \
 \

Intake manifold
Ai i k h b   \
 \

Air intake chamber
Th l b d   \
 \

Throttle body
ISC l\

ISC valve
Bkb li   \
 \

Brake booster line
2L i i ifi   \
 \
2. Lean mixture causing misfire
 High High Rough idle\
 \
1. Clogged air filter g g g
(Black smoke from exhaust)\
 \
gg
2. Faulty EFI systems:   ()\
 \
yy

Faulty pressure regulator
   \
 \

yg

Clogged fuel return line
   \
 \

gg

Defective water temp. sensor
   \
 \

Defective air temp. sensor
   \
 \

Faulty ECU
   \
 \

y

Faulty injectors
\

yj

Faulty cold start injector   \
 \
yj

Faulty throttle position sensor   \
 \

Faulty air flow meter
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ENGINE MECHANICAL Idle and/or 2,500 rpm HC/CO
Concentration Check MethodEM±29
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REMOVAL OF CYLINDER HEAD
(See Components on pages EM±34 and 35)1. DISCONNECT HIGH±TENSION CORDS FROM SPARK PLUGS
(See steps 1 to 8 on pages EM±10 and 11)
2. REMOVE SPARK PLUGS (See step 2 on page IG±8)
3. REMOVE DISTRIBUTOR AND CORDS
(See pages IG±11 and 12)
4. REMOVE WATER PUMP PULLEY AND RADIATOR (See steps 1 to 3, 6 and 7 on pages EM±64 to 66)
5. DISCONNECT TIMING BELT FROM CAMSHAFT TIMING PULLEYS
(See steps 2 to 5 on pages EM±24 and 25)
NOTICE:
wSupport the timing belt, so that the meshing of the
crankshaft timing pulley and timing belt does not shift.
w Be careful not to drop anything inside the timing belt
cover.
w Do not allow the timing belt to come into contact with oil,
water or dust.
6. REMOVE NO. 2 FRONT EXHAUST PIPE (See step 2 on page EM±71)
7. REMOVE EXHAUST MANIFOLDS (a) Disconnect the two oxygen sensor connectors.
(b) Remove the four nuts and manifold heat insulator.
(c) Remove the four nuts, exhaust manifold and gasket.Remove the No. 1 and No. 2 exhaust manifolds.
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16. INSTALL EXHAUST MANIFOLD(a) Install a new gasket and the exhaust manifold with thefour nuts. Install the No. 1 and No. 2 exhaust manifolds.
Torque: 39 N Vm (400 kgf Vcm, 29 ft Vlbf)
(b) Install the manifold heat insulator with the four nuts.
Torque: 18 N Vm (185 kgf Vcm, 13 ft Vlbf)
(c) Connect the two oxygen sensor connectors.
17. INSTALL NO. 2 FRONT EXHAUST PIPE (See step 5 on page EM±105)
18. INSTALL TIMING BELT (See steps 8 to 14 on pages EM±30 to 33)
19. INSTALL RADIATOR AND WATER PUMP PULLEY (See steps 15, 16, 19 and 24 on pages EM±110 to 112)
20. INSTALL SPARK PLUGS (See step 6 on page IG±9)
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
21. CONNECT HIGH±TENSION CORDS TO SPARK PLUGS
(See steps 14 to 21 on pages EM±17 to 21)
22. FILL ENGINE WITH COOLANT (See page CO±5)
Capacity (w/ Heater): M/T 8.5 liters (9.0 US qts, 7.5 lmp. qts)
A/T 8.4 liters (8.9 US pts, 7.4 lmp. qts)
23. START ENGINE AND CHECK FOR LEAKS
24. (A/T)CHECK AUTOMATIC TRANSMISSION FLUID LEVEL
(See page MA±11)
NOTICE: Do not overfill.
25. CHECK IGNITION TIMING (See page IG±14)
Ignition timing: 105 BTDC @ idle
(w/ Terminals TE1 and E1 connected)
26. PERFORM ROAD TEST Check for abnormal noise, shock, slippage, correct shift
points and smooth operation.
27. RECHECK ENGINE COOLANT LEVEL
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