1991 LEXUS SC400 Service Repair Manual

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Page 2225 of 4087

LEXUS SC400 1991 Service Repair Manual
28. REINSTALL RH NO.3 TIMING BELT COVER(a) Install the three gaskets to the timing belt cover.
(b) Fit portion A of the timing belt cover, matching it with the
lower high±tension cord cover.
(c)

Page 2226 of 4087

LEXUS SC400 1991 Service Repair Manual
35. REINSTALL LH ENGINE WIRE COVER(a) Connect portions A and B engine wire cover to the wirebrackets.
(b) Set the VSV (for fuel pressure control system) wire in
original position.
(c) Fit portio

Page 2227 of 4087

LEXUS SC400 1991 Service Repair Manual
38. RECONNECT CONTROL CABLES TO THROTTLE BODYConnect the following hoses:(1) Accelerator cable
(2) A/T throttle control cable
(3) (w/ Cruise Control System) Cruise control actuator cable
39. REINST

Page 2228 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 2229 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 2230 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 2231 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)

Page 2232 of 4087

LEXUS SC400 1991 Service Repair Manual
9. RECONNECT RH CAM POSITION SENSOR CONNECTOR
(a) Connect the sensor connector.
(b) Connect the connector to the ignition coil bracket.
10. RECONNECT LH CAM POSITION SENSOR CONNECTOR
11. RECONNEC

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