1991 LEXUS SC400 oxygen sensor

(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.
EM±126
±
ENGINE MECHANICAL Cylinder Block
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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.
±
ENGINE MECHANICAL Cylinder BlockEM±169
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TORQUE SPECIFICATIONS
\
 \
Part tightened NVm kgf Vcm ft Vlbf
 No.1 idler pulley X Cylinder block  34 350 25
No.2 idler pulley X Cylinder block3435025 Hydraulic pump X Cylinder block 12 mm head 16 160 12  14 mm head 30 310 22
 Crankshaft pulley X Crankshaft  245 2,500 181
Camshaft timing pulley X Camshaft1081,10080 Timing belt tensioner X Oil pump  26 270 20 Spark plug X Cylinder head  18 180 13
 Drive belt tensioner X Cylinder block  16 160 12
Alternator X Alternator bracket3738027 Alternator X Cylinder block  37 380 27 Distributor housing X Cylinder head  18 185 13
 Distributor rotor X Distributor housing   3.8 39  34 in. Vlbf
Distributor cap X Camshaft timing pulley 3.839 34 in. Vlbf\
 \
RH No.2 timing belt cover X Cylinder block (for 12 mm head) 16 160 12 Drive belt idler pulley X Hydraulic pump  37 380 27
 A/C compressor X Hydraulic pump  49 500 36
A/C compressor X Cylinder block4950036 A/C compressor stay X Oil filter bracket  29 300 22 Exhaust manifold X Cylinder head  39 400 29
 Main oxygen sensor X Exhaust manifold  44 450 33
Cylinder head X Cylinder block1st3940029  2nd Turn 90 5  
 Camshaft bearing cap X Cylinder head  16 160 12
 Cylinder head cover X Cylinder head   5.9 60  52 in. Vlbf
Engine hanger X Cylinder head3738027 EGR pipe X Exhaust manifold  18 185 13 Rear water by±pass joint X Cylinder head  18 185 13
 Front water by±pass joint X Cylinder head  18 185 13
Intake manifold X Cylinder head1818513 Delivery pipe X Intake manifold  18 185 13\
 \
Fuel return pipe X RH delivery pipe(for union bolt) 35 360 26
 Fuel inlet hose X LH delivery pipe  39 400 29
for SST3334024 Cold start injector X Air intake chamber   7.8 80  69 in. Vlbf Air intake chamber X Intake manifold  18 185 13
 EGR pipe X Air intake chamber  18 185 13
EGR pipe X RH cylinder head1818513 Cold start injector tube X RH delivery pipe  15 150 11 Brake booster union X Air intake chamber  29 300 22
 Throttle body X Air intake chamber  18 185 13
ISC valve X Air intake chamber1818513 EGR valve adapter X Air intake chamber  18 185 13 EGR valve X EGR valve adapter  18 185 13
 Timing belt rear plate X Cylinder head   7.8 80  69 in. Vlbf
Water inlet housing X Water pump1818513\
 \
Catalytic converter (main) X Exhaust manifold 62 630 46\
 \
Catalytic converter (main) X Front exhaust pipe 43 440 32
\
 \
Front exhaust pipe support bracket X Transmission 43 440 32
PS pump X RH cylinder headBolt3940029  Nut 43 440 32 Main bearing cap X Cylinder block Nut 1st 27 275 20
  2nd Turn 90 5  
Bolt4950036
±
ENGINE MECHANICAL Service SpecificationsEM±181
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TORQUE SPECIFICATIONS (Cont'd)
\
 \
Part tightened NVm kgf Vcm ft Vlbf
 Connecting rod cap X Connecting rod 1st 25 250 18
2ndTurn 90 5 Rear oil seal retainer X Cylinder block   7.8 80  69 in. Vlbf Water seal plate X Cylinder block  14 145 10
 Alternator bracket X Cylinder block  18 185 13
 Oil pump X Cylinder block 12 mm head 16 160 12
14 mm head3031022 Water pump X Cylinder block  18 185 13 Water by±pass pipe X Cylinder block  18 185 13
 Knock sensor X Cylinder block  44 450 33
 Starter X Cylinder block  39 400 29
Engine mounting bracket X Cylinder block3738027 Drive plate X Crankshaft  98 1,000 72 A/T oil cooler pipe X Transmission  34 350 25 Rear engine mounting member X Body  25 260 19
\
 \
Rear engine mounting member X Engine mounting insulator 13 135 10
\
 \
Front engine mounting insulator X Suspension crossmember 59 600 43
Center floor brace X Body131309 Tailpipe X Center exhaust pipe  43 440 32 Front exhaust pipe X Center exhaust pipe  43 440 32
 Sub±oxygen sensor X Front exhaust pipe  44 450 33
EM±182±
ENGINE MECHANICAL Service Specifications
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The EFI system is composed of three basic sub±systems: Fuel, Air Induction and Elect\
ronic Control
Systems.
FUEL SYSTEM
An electric pump fuel pressure supplies sufficient fuel, under a constant pressure, to the EFI injectors. In
accordance with signals from the ECU (Electronic Control Unit), these \
injectors inject the quantity of fuel most
appropriate for the engine condition into the intake manifold.
AIR INDUCTION SYSTEM
The air induction system provides sufficient air for engine operation.
ELECTRONIC CONTROL SYSTEM
The 1UZ±FE engine (ECU±formerly EFI computer) with a microcomputer \
centrally controls the EFI, ESA,
ISC and Diagnosis system, etc. The ECU controls the following functions:
1. Electronic Fuel Injection (EFI)
The ECU receives signals from various sensors indicating changing engine op\
eration conditions such as:Intake air volume
Intake air temperature
Coolant temperature
Engine rpm
Acceleration/deceleration
Exhaust oxygen content etc.
The signals are utilized by the ECU to determine the injection duration nec\
essary for an optimum air±fuel
ratio.
2. Electronic Spark Advance (ESA) The ECU is programmed with data for optimum ignition timing under any and all opera\
ting conditions. Using
data provided by sensors which monitor various engine functions (rpm, coola\
nt temperature, etc.), the
Electronic Control Unit (ECU) triggers the spark at precisely right instant. (S\
ee IG section)
3. Idle Speed Control (ISC) The ECU is programmed with idle speed data for various engine conditions (\
coolant temperature, air condi-
tioner ON/OFF, etc.).
The air volume flowing through the throttle valve by±pass passage is adj\
usted according to the signal from
each sensor and the idle speed is kept at the set value.
4. Diagnosis Function When the ECU detects any malfunctions or abnormalities in the sensor network\
, it lights the ºCHECKº en-
gine warning light in the combination meter. At the same time, the trouble is identified and a diagnostic code
is recorded by the ECU. The diagnostic code can be read by the number of\
blinks of the ºCHECKº engine
warning light when terminals TE1 and E1 are connected. The diagnostic co\
des are refer to the later page.
(See TR section)
5. Self±Correction Function If any sensor malfunctions, an average value recorded in the back±up ci\
rcuit is substituted to make driving
possible.
If danger is predicted, the engine is stopped and the ºCHECKº engine\
warning light will light up.
6. Fail±Safe Function Even if an abnormality occurs in the ECU, the back±up circuit uses a specifie\
d fuel injection and ignition
timing to provide vehicle driveability, and also lightsup the ºCHECKº engine warning light.
FI±4
EFI SYSTEM
± Description
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ELECTRONIC CONTROL SYSTEM
The control system consists of sensors which detect various engine conditions, and a ECU which deter\
-
mines the injection volume (timing) based on the signals from the sens\
ors.
The various sensors detect the air intake volume, engine rpm, oxygen densit\
y in the exhaust gas, coolant
temperature, air intake temperature and atmospheric pressure etc. and convert the in\
formation into an electrical
signal which is sent to the ECU. Based on these signals, the ECU calculates th\
e optimum ignition timing for the
current conditions and operates the injectors.
The ECU not only controls the fuel injection timing, but also the self diag\
nostic function which records the
occurrence of a malfunction, ignition timing control, idle rpm control, \
EGR control, EVAP control, fuel pressure
control and fuel pump control. FI±9
EFI SYSTEM
± Operation
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PRECAUTIONS
1. Before working on the fuel system, disconnect the cablefrom negative (±) terminal of the battery.
HINT: Any diagnostic code retained by the computer will be
erased when the battery terminal is removed. Therefore, if
necessary, read the diagnosis before removing the battery
terminal.
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 negative (±) terminal
cable is disconnected from the battery.
2. Do not smoke or work on open flame when working on the fuel system.
3. Keep gasoline away from rubber or leather parts.
INSPECTION PRECAUTIONS
MAINTENANCE PRECAUTIONS
1. CHECK CORRECT ENGINE TUNE±UP (See page EM±8)
2. PRECAUTIONS WHEN CONNECTING GAUGE (a) Use the battery as the power source for the timing light,tachometer, etc.
(b) Connect the test probe of a tachometer to the terminal IG of the check connector.
3. IN EVENT OF ENGINE MISFIRE, FOLLOWING PRECAUTIONS SHOULD BE TAKEN
(a) Check proper connection of battery terminals, etc.
(b) Handle high±tension cords carefully.
(c) After repair work, check that the ignition coil terminalsand all other ignition system lines are reconnected
securely.
(d) When cleaning the engine compartment, be especially careful to protect the electrical system from water.
4. PRECAUTIONS WHEN HANDLING OXYGEN SENSOR (a) Do not allow oxygen sensor to drop or hit against anobject.
(b) Do not allow the sensor to come into contact with water.
FI±12
± Precautions, Inspection PrecautionsEFI SYSTEM
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Main Oxygen Sensors
INSPECTION OF MAIN OXYGEN
SENSORS
1. WARM UP ENGINEAllow the engine to warm up to normal operating
temperature.
2. INSPECT FEEDBACK VOLTAGE Connect the positive (+) probe of a voltmeter to terminal VF1
(for LH bank) or VF2 (for RH bank) of the check (ºDIAGNO-
SISº) connector, and negative (±) probe to terminal E1. Per-
form the test as follows described on the next page.
HINT: Use SST when connecting between terminals TE1 and
E1 of the check connector.
SST 09843±18020 FI±113
± Electronic Control System (\
Main Oxygen Sensors)EFI SYSTEM
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