ect LEXUS SC300 1991 Service Repair Manual

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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COMPRESSION CHECK
HINT: If there is lack of power, excessive oil consumption or
poor fuel economy, measure the compression pressure.
1. WARM UP AND STOP ENGINE Allow the engine to warm up to normal operating tempera-
ture.
2. DISCONNECT DISTRIBUTOR CONNECTOR
3. DISCONNECT HIGH±TENSION CORDS FROM SPARK PLUGS (See steps 2 to 8 on pages EM±10 and 11)
4. DISCONNECT INJECTOR CONNECTORS
5. REMOVE SPARK PLUGS (See page IG±8)
6. CHECK CYLINDER COMPRESSION (a) Insert a compression tester into the spark plug hole.
(b) Fully open the throttle.
(c) While cranking the engine, measure the compressionpressure.
HINT: Always use a fully charged battery to obtain engine rev-
olution of 250 rpm or more.
(d) Repeat steps (a) through (c) for each cylinder.
NOTICE: This measurement must be done in as short
time as possible.
Compression:
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
(e) If the cylinder compression in one or more cylinders islow, pour a small amount of engine oil into the cylinder
through the spark plug hole and repeat steps (a) through
(c) for the cylinder with low compression.
w If adding oil helps the compression, the piston rings
and/or cylinder bore are probably worn or
damaged.
w If pressure stays low, a valve may be sticking or
seating improper, or there may be leakage past the
gasket.
7. REINSTALL SPARK PLUGS (See page IG±9)
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
8. RECONNECT INJECTOR CONNECTORS
9. RECONNECT HIGH±TENSION CORDS TO SPARK
PLUGS (See steps 14 to 20 on pages EM±17 to 19)
10. RECONNECT DISTRIBUTOR CONNECTOR
EM±22
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ENGINE MECHANICAL Compression Check
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(a) Alternately loosen the two bolts, and remove them, thetensioner and dust boot.
(b) Disconnect the timing belt from the camshaft timing pulleys.
6. REMOVE CAMSHAFT TIMING PULLEYS Using SST, remove the bolt for the timing pulley. Remove
both timing pulleys.
SST 09278±54012
7. REMOVE CRANKSHAFT PULLEY (a) Using SST to hold the crankshaft pulley, loosen thepulley mounting bolt.
SST 09213±54015 (91651±60855) and 09330±00021
(b) Remove SST and pulley bolt.
(c) Using SST, remove the pulley.
SST 09213±31021
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ENGINE MECHANICAL Timing BeltEM±25
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8. REMOVE NO. 1 TIMING BELT COVERRemove the five bolts, timing belt cover and two gaskets.
9. REMOVE TIMING BELT GUIDE
10. REMOVE TIMING BELT HINT (When re±using timing belt): Draw an arrow on the tim-
ing belt in the direction of engine revolution, and place match-
marks on the timing belt and crankshaft timing pulley.
11. REMOVE IDLER PULLEY Using a 10 mm hexagon wrench, remove the pivot bolt, plate
washer and idler pulley.
12. REMOVE CRANKSHAFT TIMING PULLEY If the pulley cannot be removed by hand, use SST to remove
the crankshaft timing pulley.
SST 09213±60017 (09213±00020, 09213±00030,09213±00040, 09213±00050)
EM±26
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ENGINE MECHANICAL Timing Belt
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INSPECTION OF TIMING BELT
COMPONENTS
1. INSPECT TIMING BELTNOTICE:w Do not bend, twist or turn the timing belt inside
out.
w Do not allow the timing belt to come into contact
with oil, water or steam.
w Do not make use of timing belt tension when
installing or removing the mount bolt of the
camshaft timing pulley.
If there are any defects as shown in the illustrations, check
the following points:
(a) Premature parting
w Check for proper installation.
w Check the timing cover gasket for damage and
proper installation.
(b) If the belt teeth are cracked or damaged, check to see if either the camshaft or water pump is locked.
(c) If there is noticeable wear or cracks on the belt face, check to see if there are nicks on the side of the idler
pulley lock.
(d) If there is wear or damage on only one side of the belt, check the belt guide and the alignment of each pulley.
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ENGINE MECHANICAL Timing BeltEM±27
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(e) If there is noticeable wear on the belt teeth, check thetiming cover for damage, correct gasket installation and
foreign material on the pulley teeth.
If necessary, replace the timing belt.
2. INSPECT IDLER PULLEY Check the turning smoothness of the idler pulley.
If necessary, replace the idler pulley.
3. INSPECT DRIVE BELT TENSIONER Check the turning smoothness of the tensioner.
If necessary, replace the tensioner.
4. INSPECT TIMING BELT TENSIONER (a) Visually check tensioner for oil leakage.
HINT: It is normal for a tensioner to show a small trance of oil
on the pushrod seal.
However, if there is an outright oil leak, the tensioner must be
replaced.
(b) Hold the tensioner with both hands, and push the push rod firmly against the floor or wall to check that it doesn't
move.
If the push rod moves, replace the tensioner.
EM±28
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ENGINE MECHANICAL Timing Belt
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(c) Measure the protrusion of the push rod from housingend.
Protrusion: 7.7±10.5 mm (0.303±0.413 in.)
If the protrusion is not as specified, replace the tensioner.
INSTALLATION OF TIMING BELT
(See Components page EM±23)1. INSTALL CRANKSHAFT TIMING PULLEY (a) Align the pulley set key with the key groove of the pulley.
(b) Slide on the timing pulley facing the flange side inward.
2. INSTALL IDLER PULLEY (a) Apply adhesive to two or three threads of the pivot bolt.
Adhesive: Part No. 08833±00080, THREE BOND 1344, LOCTITE 242 or equivalent
(b) Using a 10 mm hexagon wrench, install the plate washer
and pulley with the pivot bolt.
Torque: 34 N Vm (350 kgf Vcm, 25 ft Vlbf)
(c) Check that the pulley bracket moves smoothly.
3. TEMPORARILY INSTALL TIMING BELT NOTICE: The engine should be cold.
(a) Use the crankshaft pulley bolt to turn the crankshaft andalign the timing marks on the crankshaft timing pulley
and on the oil pump body.
(b) Remove any oil or water on the crankshaft timing pulley and idler pulley, and keep them clean.
(c) Install the timing belt on the crankshaft timing pulley and
idler pulley.
HINT (When re±using timing belt): Align the matchmarks of
the crankshaft timing pulley and timing belt, and install the
belt with the arrow pointing in the direction of engine revolu-
tion.
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ENGINE MECHANICAL Timing BeltEM±29
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14. INSTALL NO. 2 AND NO. 3 TIMING BELT COVERS(a) Install the gasket on the timing belt cover.
(b) Using a 5 mm hexagon wrench, install the belt coverswith the nine bolts.
(c) Install the oil filler cap.
15. INSTALL RADIATOR AND WATER PUMP PULLEY (See steps 15, 16, 19 and 24 on pages EM±110 to 112)
16. FILL ENGINE WITH COOLANT (See page CO±5)
Capacity (w/ Heater):
M/T 8.5 liters (9.0 US qts, 7.5 Imp. qts)
A/T 8.4 liters (8.9 US qts, 7.4 Imp. qts)
17. (A/T)CHECK AUTOMATIC TRANSMISSION FLUID LEVEL
(See page MA±11)
NOTICE: Do not overfill.
18. START ENGINE AND CHECK FOR LEAKS
19. CHECK IGNITION TIMING (See page IG±14)
Ignition timing:
105 BTDC @ idle
(w/ Terminals TE1 and E1 connected)
20. PERFORM ROAD TEST Check for abnormal noise, shock, slippage, correct shift
points and smooth operation.
21. RECHECK ENGINE COOLANT LEVEL
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ENGINE MECHANICAL Timing BeltEM±33
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IDLE AND/OR 2,500 RPM HC/CO
CONCENTRATION CHECK METHOD
HINT: This check is used only to determine whether or not the
idle HC/CO complies with regulations.
1. INTIAL CONDITIONS (a) Engine at normal operating temperature.
(b) Air cleaner installed.
(c) All pipes and hoses of air induction system connected.
(d) All accessories switched OFF.
(e) All vacuum lines properly connected.
HINT: All vacuum hoses for EGR systems, etc. should be
properly connected.
(f) EFI system wiring connectors fully plugged.
(g) Transmission in neutral range.
(h) Tachometer and HC/CO meter calibrated at hand.
2. START ENGINE
3. RACE ENGINE AT 2,500 PRM FOR APPROX. 120 SECONDS
4. INSERT HC/CO METER TESTING PROBE INTO TAILPIPE AT LEAST 40 cm (1.3 ft)
5. CHECK HC/CO CONCENTRATION AT IDLE AND/OR 2,500 PRM
Complete the measuring within three times.
HINT: When performing the 2 mode (2,500 rpm and idle) test,
follow the measurement order prescribed by the regulations.
If the HC/CO concentration at 2,500 rpm does not comply
with regulations, try the following procedure.
Race the engine again at 2,500 rpm for approx. 1 minute and
quickly repeat steps 4 and 5 above.
This may correct the problem.
EM±28
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ENGINE MECHANICAL Idle and/or 2,500 rpm HC/CO
Concentration Check Method
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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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