1991 LEXUS SC400 sensor

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


 


 


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


 


 


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


 


 


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

High 

High 

Rough idle\
 

\
1. Restricted air filter
   (Black smoke from exhaust)\
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2. Faulty MFI systems:
   \
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Faulty pressure regulator
   \
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Clogged fuel return line
   \
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Defective ECT switch   \
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Faulty ECM 


 


 


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Faulty injector
   \
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Faulty throttle position sensor
   \
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Faulty volume air flow meter
V02130
EG±36±
1UZ±FE ENGINE ENGINE MECHANICAL
WhereEverybodyKnowsYourName

10. DISCONNECT COLD START INJECTOR CONNECTOR
11. DISCONNECT RH CAMSHAFT POSITION SENSORCONNECTOR
(a) Disconnect the connector from the ignition coil bracket.
(b) Disconnect the camshaft position sensor connector.
12. D I S C O N N E C T L H C A M S H A F T P O S I T I O N S E N S O R
CONNECTOR
13. DISCONNECT HIGH±TENSION CORDS FROM SPARK PLUGS
Disconnect the high±tension cords at the rubber boot. Do not
pull on the cords.
NOTICE: Pulling on or bending the cords may damage the con-
ductor inside.
14. REMOVE SPARK PLUGS Using a 16 mm plug wrench, remove the 8 spark plugs.
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1UZ±FE ENGINE ENGINE MECHANICALEG±39
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15. CHECK CYLINDER COMPRESSION PRESSURE
(a) Reconnect the battery negative (±) cable.
(b) Insert a compression gauge into the spark plug hole.
(c) Fully open the throttle.
(d) Wh ile cra n kin g th e en g in e , me a su re th e co mp re ssio npressure.
HINT: Always use a fully charged battery to obtain engine
speed of 250 rpm or more.
(e) Repeat steps (b) through (d) for each cylinder. NOTICE: This measurement must be done in as short a
time as possible.
Compression pressure:
1,226 kPa (12.5 kgf/cm
2, 178 psi) or more
Minimum pressure: 981 kPa (10.0 kgf/cm
2, 142 psi)
Difference between each cylinder: 98 kPa (1.0 kgf/cm
2, 14 psi) or less
(f) If the cylinder compression in one or more cylinders is low,pour a sm all amount of engine oil into the cylinder through the
spark plug hole and repeat steps (b) through (d) for cylinders
with low compression.
w If adding oil helps the compression, it is likely that the
piston rings and/or cylinder bore are worn or damage.
w If pressure stays low, a valve may be sticking or seating
is improper, or there may be leakage past the gasket.
(g) Disconnect the battery negative (±) cable.
16. REINSTALL SPARK PLUGS
Using a 16 mm plug wrench, install the 8 spark plugs.
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
17. R E C O N N E C T H I G H ± T E N S I O N C O R D S TO S PA R K
PLUGS
18. RECONNECT RH CAMSHAFT POSITION SENSOR CONNECTOR
(a) Connect the camshaft position sensor connector.
(b) Install the camshaft position sensor connector to the ignition
coil bracket.
EG±40
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19. RECONNECT LH CAMSHAFT POSITION SENSORCONNECTOR
20. RECONNECT COLD START INJECTOR CONNECTOR
21. REINSTALL RH NO.3 TIMING BELT COVER
(a) Install the 3 gaskets to the timing belt cover.
(b) Fit the portion A of the timing belt cover, matching it with the lower high±tension cord cover.
(c) Install the timing belt cover with the 3 bolts.
22. REINSTALL VSV FOR EVAP SYSTEM Install the VSV with the 2 bolts.
23. REINSTALL LH NO.3 TIMING BELT COVER
(a) Install the 3 gaskets to the timing belt cover.
(b) Install the cord grommet to the high±tension cord (from the LH ignition coil).
(c) Install the cord grommet to the timing belt cover.
(d) Fit the portion A of the timing belt cover, matching it with the lower high±tension cord cover.
(e) Install the timing belt cover with the 4 bolts.
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EG21P±02
TIMING BELT REMOVAL
(See Components for Removal and Installation)
1. REMOVE BATTERY CAUTION: Work must be started after 90 seconds from
the time the ignition switch is turned to the ªLOCKº posi-
tion and the negative (±) terminal cable is disconnected
from the battery.
2. REMOVE ENGINE UNDER COVER
3. DRAIN ENGINE COOLANT
4. REMOVE DRIVE BELT
Loosen the drive belt tension by turning the drive belt tension-
er counterclockwise, and remove the drive belt.
HINT: The pulley bolt for the drive belt tensioner has a left±
hand thread.
5. REMOVE RADIATOR RESERVOIR TANK
(a) Disconnect the coolant level sensor connector.
(b) Disconnect the following hoses: (1) Reservoir hose from water inlet housing
(2) Reservoir hose from radiator
(c) Remove the 2 bolts and reservoir tank bracket.
(d) Remove the bolt holding the reservoir tank to the radiator.
(e) Disconnect the reservoir tank from the reservoir tank bracket,
and remove the reservoir tank.
6. REMOVE RADIATOR ASSEMBLY
(a) Disconnect the ECT sensor connector (for cooling fan).
(b) Disconnect the ECT sensor wire clamp from the radiator fan shroud.
EG±46
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1UZ±FE ENGINE ENGINE MECHANICAL
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20. REMOVE DISTRIBUTOR CAPSLoosen the 3 bolts, and remove the distributor cap.
Remove the 2 distributor caps.
HINT: Arrange the distributor caps (RH side and LH side).
21. REMOVE DISTRIBUTOR ROTORS Loosen the 2 bolts, and remove the distributor rotor.
Remove the 2 distributor rotors.
HINT: Arrange the distributor rotors (RH side and LH side).
22. REMOVE DISTRIBUTOR HOUSINGS
(a) RH Distributor Housing: Disconnect the camshaft position sensor connector.
(b) Remove the 3 bolts and distributor housing. Remove the 2 distributor housings.
23. REMOVE GENERATOR
(a) Disconnect the generator connector.
(b) Remove the cap and nut, and disconnect the generator wire.
(c) Remove the bolt, and disconnect the transmission oil cooler pipe bracket from the generator.
(d) Remove the nut and generator.
24. REMOVE DRIVE BELT TENSIONER Remove the bolt, 2 nuts and belt tensioner.
EG±52
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31. REMOVE CRANKSHAFT PULLEY
(a) Using SST, remove the pulley bolt.SST 09213±70010, 09330±00021
(b) Using SST, remove the crankshaft pulley. SST 09213±31021
32. REMOVE HYDRAULIC PUMP HINT (When re±using timing belt): Before removing the hy-
draulic pump, using the crankshaft pulley bolt, turn the crank-
shaft pulley and align the installation mark of the timing belt
with the end of the hydraulic pump.
(a) Disconnect the solenoid valve connector.
(b) Remove the 2 bolts and 2 nuts.
(c) Disconnect the crankshaft position sensor wire clamp.
(d) Remove the hydraulic pump.
33. REMOVE NO.1 TIMING BELT COVER Remove the 4 bolts, timing belt cover and gasket.
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1UZ±FE ENGINE ENGINE MECHANICALEG±55
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34. REMOVE TIMING BELT COVER SPACERRemove the belt cover spacer and gasket.
35. REMOVE TIMING BELT GUIDE (CRANKSHAFT ANGLE SENSOR PLATE)
36. REMOVE TIMING BELT HINT (When re±using timing belt): If the installation marks
have disappeared, place a new installation mark on the tim-
ing belt to the match the dot mark of the crankshaft timing
pulley.
37. REMOVE NO.2 IDLER PULLEY Remove the bolt and idler pulley.
38. REMOVE NO.1 IDLER PULLEY Using a 10 mm hexagon wrench, remove the bolt, idler pulley
and plate washer.
EG±56
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1UZ±FE ENGINE ENGINE MECHANICAL
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