1991 LEXUS SC400 Service Repair Manual

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Page 1697 of 4087

LEXUS SC400 1991 Service Repair Manual
4. INSTALL TIMING BELT GUIDEInstall the guide, facing the cup side outward.
5. INSTALL NO. 1 TIMING BELT COVER (a) Install the two gaskets to the timing belt cover.
(b) Install the timing belt cov

Page 1698 of 4087

LEXUS SC400 1991 Service Repair Manual
(b) Turn the camshaft, and align the timing marks of thecamshaft timing pulleys and No. 4 timing belt cover.
SST 09278±54012
9. INSTALL TIMING BELT HINT (When re±using timing belt): Align the mat

Page 1699 of 4087

LEXUS SC400 1991 Service Repair Manual
11. INSTALL TIMING BELT TENSIONER(a) Temporarily install the tensioner with the two bolts.
(b) Alternately tighten the two bolts.
Torque: 26 N Vm (270 kgf Vcm, 20 ft Vlbf)
(c) R e m o v e t h e 1

Page 1700 of 4087

LEXUS SC400 1991 Service Repair Manual
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 fil

Page 1701 of 4087

LEXUS SC400 1991 Service Repair Manual
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 o

Page 1702 of 4087

LEXUS SC400 1991 Service Repair Manual
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 tabl

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
±
ENGINE MECHANICAL Idle and/or 2,500 rpm HC/CO
Concentration Check MethodEM±29
WhereEverybodyKnowsYourName

Page 1703 of 4087

LEXUS SC400 1991 Service Repair Manual
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

Page 1704 of 4087

LEXUS SC400 1991 Service Repair Manual
(b) Using a 16 mm spark plug wrench, remove the eightspark plugs.
7. CHECK CYLINDER COMPRESSION PRESSURE (a) Insert a compression tester into the spark plug hole.
(b) Fully open the throttle.
(c)

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