LEXUS SC400 1991 Service Repair Manual

IDLE AND/OR 2,500 RPM CO/HC
CHECK
EG116±05
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 system, etc. should be prop-
erly connected.
(f) MFI system wiring connectors fully plugged
(g) Ignition timing set correctly
(h) Transmission in neutral position
(i) Tachometer and CO/HC meter calibrated by hand
2. START ENGINE
3. RACE ENGINE AT 2,500 RPM FOR APPROX. 180 SECONDS
4. INSERT CO/HC METER TESTING PROBE INTO TAILPIPE AT LEAST 40 cm (1.3 ft) DURING IDLING
5. IMMEDIATTELY CHECK CO/HC CONCENTRATION AT
IDLE AND/OR 2,500 RPM
HINT: When performing the 2 mode (2,500 rpm and idle) test,
follow the measurement order prescribed by the applicable
local regulations.
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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\
 \
Causes
 Normal High Rough idle\
 \
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   \
 \
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\
 \
1. Vacuum leaks:
   (Fluctuating HC reading)\
 \

PCV hose
   \
 \
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)\
 \
2. Faulty MFI systems:
   \
 \

Faulty pressure regulator
   \
 \
Clogged fuel return line
   \
 \
Defective ECT switch   \
 \
Faulty ECM 


 


 


\
 

\

Faulty injector
   \
 \
Faulty throttle position sensor
   \
 \
Faulty volume air flow meter
V02130
EG±36±
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COMPRESSION CHECK
EG21U±02
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 NEGATIVE TERMINAL CABLE FROM 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.
3. REMOVE INTAKE AIR CONNECTOR
(a) Disconnect the following hoses: (1) Air hose from IAC valve
(2) Air hose (from air control valve on PS pump) from intake
air connector
(b) Remove the bolt holding the intake air connector to the cylinder head cover.
(c) Remove the 2 hose clamps.
(d) Disconnect the intake air connector from the throttle body
and air cleaner hose, and remove the intake air connector.
4. REMOVE UPPER HIGH±TENSION CORD COVER
(a) Remove the 2 bolts.
(b) Disconnect the front side claw groove of the upper cord cover
from the claw of lower cord cover, and remove the upper cord
cover.
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5. REMOVE RH ENGINE WIRE COVERRemove the bolt and engine wire cover.
6. REMOVE LH ENGINE WIRE COVER Remove the 2 bolts and engine wire cover.
7. REMOVE VSV FOR EVAP SYSTEM Remove the 2 bolts, and disconnect the VSV from the cylin-
der head cover and timing belt cover.
8. REMOVE RH NO.3 TIMING BELT COVER Remove the 3 bolts, timing belt cover and 3 gaskets.
9. REMOVE LH NO.3 TIMING BELT COVER
(a) Remove the 4 bolts
(b) Disconnect the cord grommet from the timing belt cover, and remove the timing belt cover and 3 gaskets.
(c) Remove the cord grommet from the high±tension cord.
EG±38
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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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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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24. REINSTALL RH ENGINE WIRE COVER
(a) Fit portions A and B of the engine wire cover, matching themwith the lower high±tension cord cover and No.3 timing belt
cover.
(b) Install the timing belt cover with the bolt.
25. REINSTALL LH ENGINE WIRE COVER
(a) Connect portions A and B of the engine wire cover to the wire
brackets.
(b) Set the VSV (for the fuel pressure) wire in original position.
(c) Fit portions C and D of the engine wire cover, matching them with the lower high±tension cord cover and No.3 timing belt
cover.
(d) Install the timing belt cover with the 2 bolts.
26. REINSTALL UPPER HIGH±TENSION CORD COVER
(a) Fit portion A of the upper high±tension cord cover matching the top of the lower high±tension cord cover.
(b) Push the front side of the upper high±tension cord cover, and
fit the front side claw groove of the upper high±tension cord
cover to the claw of the lower high ±tension cord cover.
(c) Install the upper high±tension cord cover with the 2 bolts.
27. REINSTALL INTAKE AIR CONNECTOR
(a) Connect the end portions of the intake air connector to the throttle body and air cleaner hose.
(b) Tighten the 2 hose clamps.
(c) Install the bolt holding the intake air connector to the cylinder head cover.
EG±42
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(d) Connect the following hoses:(1) Air hose to IAC valve
(2) Air hose (from air control valve on PS pump) to intake air
connector
28. RECONNECT NEGATIVE TERMINAL CABLE TO BATTERY
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TIMING BELT
EG21Q±01
COMPONENTS FOR REMOVAL AND
INSTALLATION
EG±44±
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