vacuum LEXUS SC400 1991 Service Manual PDF

IDLE AND/OR 2,500 RPM CO/HC
CHECK
HINT: This check is used only to determine whether or not the
idle CO/HC complies with regulations.
1. INITIAL 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) SFI system wiring connectors fully plugged.
(g) Transmission in neutral.
(h) Tachometer and CO/HC analyzer calibrated and athand.
2. START ENGINE
3. RACE ENGINE AT 2,500 RPM FOR APPROX. 120 SECONDS
4. INSERT CO/HC ANALYZER TESTING PROBE INTO TAILPIPE AT LEAST 40 cm (1.3 ft)
5. CHECK CO/HC CONCENTRATION AT IDLE AND/OR
2,500 RPM
Complete the measuring within three minutes.
HINT: When performing the two mode (2,500 rpm and idle)
test, follow the measurement order prescribed by the regula-
tions.
If the CO/HC 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±20
±
ENGINE MECHANICAL Idle and/or 2,500 rpm CO/HC Check
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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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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
±
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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8. REMOVE WATER BY±PASS OUTLET AND NO. 1 WATERBY±PASS PIPE
(a) Remove the two bolts, water by±pass outlet and No. 1water by±pass pipe.
(b) Remove the three O±rings from the water by±pass outlet and No. 1 water by±pass pipe.
9. REMOVE WATER OUTLET AND NO. 1 BY±PASS HOSE (a) Remove the two nuts, bolt and water outlet.
(b) Disc onnect the No. 1 by±pass hose from the hose
clamp.
10. REMOVE VACUUM CONTROL VALVE SET AND NO. 2 VACUUM PIPE
(a) Disconnect the two connectors from the VSV.
(b) Disconnect the following hoses:(1) Vacuum hose from ACIS vacuum tank
(2) Three vacuum hoses from VSV
(c) Remove the four nuts, vacuum control valve set and
vacuum pipe.
11. REMOVA OIL DIPSTICK GUIDES FOR ENGINE AND TRANSMISSION (A/T)
(a) Disconnect the fuel return hose from the engine oildipstick guide.
(b) Remove the mounting bolt.
(c) Pull out the dipstick guide together with dipstick. Plug the oil pan.
(d) Remove the O±ring from the dipstick guide.
12. REMOVE AIR INTAKE CHAMBER (a) Remove the bolt, nut and intake chamber stay. Removethe No. 1 and No. 2 stays.
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ENGINE MECHANICAL Cylinder HeadEM±37
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(b) Disconnect the following hoses:(1) Vacuum hose from brake booster union
(2) Vacuum hose (from ACIS vacuum tank)
(3) Vacuum sensing hose
(4) Air hose (from PS air control valve)
(c) Remove the two bolts, and disconnect the data link connector 1 and harness protector from the air intake
chamber.
(d) Remove the five bolts, two nuts and air intake chamber and gasket.
13. REMOVE DELIVERY PIPE AND INJECTORS (See steps 4, 5, 8 and 10 on pages FI±28 and 29)
14. REMOVE NO. 1 AND NO. 2 FUEL PIPES
15. DISCONNECT ENGINE WIRE FROM INTAKE MANIFOLD (a) Disconnect the following connectors:
(1) Engine coolant temperature sensor connector
(2) Engine coolant temperature sender gauge connec- tor
(3) Two knock sensor connectors
(4) Oil pressure switch connector
(5) Oil level sensor connector
(6) A/C compressor connector
(b) Remove the three nuts and two clamp bolts.
(c) Remove the two bolts, and disconnect the harness
protector from the intake manifold.
16. REMOVE INTAKE MANIFOLD (a) Remove the two bolts and intake manifold stay.
(b) Remove the six bolts, two nuts, intake manifold andgasket.
EM±38
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ENGINE MECHANICAL Cylinder Head
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8. CONNECT ENGINE WIRE TO INTAKE MANIFOLD(a) Install the harness protector to the intake manifold withthe two bolts.
(b) Install the three clamp bolts and two nuts.
(c) Connect the following connectors:
(1) Engine coolant temperature sensor connector
(2) Engine coolant temperature sender gauge connec- tor
(3) Two knock sensor connectors
(4) Oil pressure switch connector
(5) Oil level sensor connector
(6) A/C compressor connector
9. INSTALL NO. 1 AND NO. 2 FUEL PIPES
Torque: 8.8 N Vm (90 kgf Vcm, 78 in. Vlbf)
10. INSTALL DELIVERY PIPE AND INJECTORS
(See steps 1, 3, 6 and 7 on pages FI±33 and 34)
Torque: 21 N Vm (210 kgf Vcm, 15 ft Vlbf)
11. INSTALL AIR INTAKE CHAMBER
(a) Install a new gasket and the intake chamber with the five
bolts and two nuts.
Torque: 21 N Vm (210 kgf Vcm, 15 ft Vlbf)
(b) Install the check connector and harness protector to the
air intake chamber with the two bolts.
(c) Connect the following hoses: (1) Vacuum hose to brake booster union
(2) Vacuum hose (to ACIS vacuum tank)
(3) Vacuum sensing hose
(4) Air hose (to PS air control valve)
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ENGINE MECHANICAL Cylinder HeadEM±59
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(d) Install the intake chamber stay with the bolt and nut.Install the No. 1 and No. 2 stay.
Torque: 18 N Vm (185 kgf Vcm, 13 ft Vlbf)
HINT: The No. 1 stay is marked ºFº and No. 2 stay is marked
with ºRº.
12. INS TALL OIL DIP S TICK GUIDE S FO R ENG INE AND TRANSMISSION (A/T)
(a) Install a new O±ring on the dipstick guide.
(b) Apply soapy water on the O±ring.
(c) Connect the dipstick guide end to the tube of the oil pan.
(d) Install the dipstick guide with a bolt.
(e) Connect the fuel return hose to the engine oil dipstick guide.
13. INSTALL VACUUM CONTROL VALVE SET AND NO. 2 VACUUM PIPE
(a) Install the vacuum control valve set and vacuum pipewith the four nuts.
Torque: 21 N Vm (210 kgf Vcm, 15 ft Vlbf)
(b) Connect the following hoses:
(1) Vacuum hose to ACIS vacuum tank
(2) Three vacuum hoses to VSV
(c) Connect the two connectors to the VSV.
14. INSTALL WATER OUTLET AND NO. 1 BY±PASS HOSE (a) Insert the No. 1 by±pass hose to the intake manifold,and connect the hose to the clamp.
(b) Install the water outlet with the two nuts and bolt.
Torque: 21 N Vm (210 kgf Vcm, 15 ft Vlbf)
15. INSTALL WATER BY±PASS OUTLET AND NO. 1 WATER
BY±PASS PIPE
(a) Install two new O±rings to the No. 1 water by±pass pipe.
(b) Install a new O±ring and the water by±pass outlet with the two bolts.
Torque: 8.8 N Vm (90 kgf Vcm, 78 in. Vlbf)
EM±60±
ENGINE MECHANICAL Cylinder Head
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REMOVAL OF CYLINDER HEADS
(See Components on pages EM±58 and 59)
1. DISCONNECT TIMING BELT FROM CAMSHAFT TIMING PULLEYS
(See steps 1 to 28 on pages EM±35 to 42)
2. REMOVE CAMSHAFT TIMING PULLEYS AND HYDRAULIC PUMP
(See steps 29 and 31 on pages EM±42 and 43)
HINT:
w Be careful not to drop anything inside the timing belt
cover.
w Do not allow the timing belt to come into contact with oil,
water or dust.
3. DISCONNECT PS PUMP FROM LH CYLINDER HEAD (a) Disc onnect the vacuum hose from the air intake
chamber.
(b) Remove the three bolts and nut, and disconnect the PS pump.
HINT: Put aside the PS pump, and suspend it.
4. REMOVE CATALYTIC CONVERTERS (MAIN) (a) Remove the four bolts holding the pipe support bracketto the transmission.
(b) Remove the four bolts and nuts holding the catalytic converters to the front exhaust pipe. Remove the pipe
support bracket.
(c) Disconnect the front exhaust pipe from the catalytic
converter, and remove the two gaskets.
(d) Remove the three nuts, catalytic converter and gasket. Remove the two catalytic converters.
EM±60
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ENGINE MECHANICAL Cylinder Heads
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9. REMOVE TIMING BELT REAR PLATESRemove the two bolts and rear plate. Remove the two rear
plates.
10. REMOVE VACUUM PIPE (a) Disconnect the following hoses:(1) (USA Spec.)
Vacuum hose from throttle body
(2) (Exc. USA Spec.) Three vacuum hoses from throttle body
(3) Vacuum hose from fuel pressure regulator
(4) Two vacuum hoses from VSV for fuel pressure con-
trol system
(5) (Exc. USA Spec.) Two vacuum hoses from EGR vacuum modulator
(6) Two vacuum hoses (from VSV for EVAP system)
from vacuum pipe
(7) Vacuum hose (from VSV for fuel pressure control system) from air intake chamber
(8) Vacuum hose (from charcoal canister) from vacu-
um pipe.
(b) Remove the two bolts, the vacuum pipe and vacuum hoses assembly.
EM±62
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ENGINE MECHANICAL Cylinder Heads
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