1991 LEXUS SC400 Service Repair Manual

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Page 1409 of 4087

LEXUS SC400 1991 Service Repair Manual
(b) Connect the tester probe of a timing light to the high ±tension
cord for No.6 cylinder.
(c) Using a timing light, check the ignition timing.
Ignition timing: 8 ± 12 5 BTDC @ idle
(Transmissi

Page 1410 of 4087

LEXUS SC400 1991 Service Repair Manual
EG115±06
IDLE SPEED INSPECTION
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 access

Page 1411 of 4087

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 t

Page 1412 of 4087

LEXUS SC400 1991 Service Repair Manual
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

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:

\

\

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 leaks:
(Fluctuating HC reading)\
\

PCV hose
\
\
EGR valve

\

\

Intake manifold
\
\
Throttle body
\
\
IAC valve
\
\
Brake booster line
\
\
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±
1UZ±FE ENGINE ENGINE MECHANICAL
WhereEverybodyKnowsYourName

Page 1413 of 4087

LEXUS SC400 1991 Service Repair Manual
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

Page 1414 of 4087

LEXUS SC400 1991 Service Repair Manual
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

Page 1415 of 4087

LEXUS SC400 1991 Service Repair Manual
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

Page 1416 of 4087

LEXUS SC400 1991 Service Repair Manual
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

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