1991 LEXUS SC400 check engine

ENGINE TUNE±UP
INSPECTION OF ENGINE COOLANT
1. INSPECT ENGINE COOLANT LEVEL AT RESERVOIRTANK
The coolant level should be above the ºCOLD LEVELº at
normal temperature (20 5C (68 5F)).
If low, check for leaks and add coolant up to the ºCOLD
LEVELº.
2. INSPECT ENGINE COOLANT QUALITY There should be any excessive deposits of rust or scales
around the radiator cap or reservoir tank filler hole, and the
coolant should be free from oil.
If excessively dirty, clean the coolant passages and replace
the coolant.
INSPECTION OF ENGINE OIL
1. INSPECT ENGINE OIL QUALITYCheck the oil for deterioration, entry of water, discoloring or
thinning.
If the quality is poor, replace the oil.
Oil grade: API grade SG, Energy±Conserving II multigrade.
Recommended viscosity is as shown, with SAE
5W±30 being the preferred engine oil.
Drain and refill oil capacity: w/ oil filter change4.8 liter (5.1 US qts, 4.2 lmp. qts)
w/o oil filter change 4.5 liter (4.8 US qts, 4.0 lmp. qts)
2. INSPECT ENGINE OIL LEVEL The oil level should be between the ºLº and ºFº marks on the
dipstick.
If low, check for leakage and add oil up to ºFº mark.
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ENGINE MECHANICAL Engine Tune±Up
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INSPECTION OF BATTERY
1. INSPECT BATTERY SPECIFIC GRAVITY ANDELECTROLYTE LEVEL
(a) Check the specific gravity of each cell.
Standard specific gravity:
1.27±1.29 when fully charged at 20 5C(68 5F)
If not within specification, charge the battery.
(b) Check the electrolyte quantity of each cell.
If insufficient, refill with distilled (or purified) water.
2. CHECK BATTERY TERMINALS Check that the battery terminals are not loose or corroded.
INSPECTION AND CLEANING OF AIR
FILTER
1. REMOVE AIR FILTER(a) Open the air cleaner cap.
(b) Remove the air filter.
2. INSPECT AIR FILTER (a) Visually check that the air filter is not excessivelydamaged or oily.
(b) Clean the air filter with compressed air.
First blow from the inside thoroughly, then blow off the out-
side of the air filter.
3. REINSTALL AIR FILTER
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ENGINE MECHANICAL Engine Tune±UpEM±9
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INSPECTION OF HIGH±TENSION CORDS
1. REMOVE HIGH±TENSION CORDS (See page IG±11)
2. INSPECT HIGH±TENSION CORDS (b) Using an ohmmeter, measure the resistance.
Maximum resistance: 25 k
per cord
If the resistance is greater than maximum, replace the cord.
3. REINSTALL HIGH±TENSION CORDS (See page IG±16)
INSPECTION OF DRIVE BELT
INSPECT DRIVE BELT
HINT: A belt tensioner is used, so checking the belt tension
is not necessary.
(a) Visually check the drive belt for excessive wear, frayedcords etc.
If necessary, replace the drive belt.
HINT:
w Cracks on rib side of a drive belt are considered
acceptable. If the drive belt has chunks missing from the
ribs, it should be replaced.
w The drive belt tension can be released by turning the
belt tensioner counterclockwise. The pulley bolt for the
belt tensioner has a left±hand thread.
(b) Check the belt tensioner operation. w Check that the belt tensioner moves downward
when the drive belt is pressed down at the points
indicated in the illustration with approx. 98 N (10
kgf, 22.0 lbf) of force.
w Check the alignment of the belt tensioner pulley to
make sure the drive belt has not slipped off the
pulley.
If necessary, replace the belt tensioner. w Check that the arrow mark on the belt tensioner
falls within area A of the scale.
If it is outside area A, replace the drive belt.
HINT:
w When a new belt is installed, it should lie within area B.
If not, the drive belt is not correct.
w After installing a belt, check that it fits properly in the
ribbed grooves.
w Check by hand to confirm that the belt has not slipped
out of the groove on the bottom of the pulley.
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(b) Check that the timing marks of the camshaft timingpulleys and timing belt rear plates aligned.
If not, turn the crankshaft one revolution (360 5) and align the
mark as above.
20. INSPECT VALVE CLEARANCE (a) Check only those valves indicated.w Using a feeler gauge, measure the clearance
between the valve lifter and camshaft.
w Record the out±of±specification valve clearance
measurements. They will be used later to
determine the required replacement adjusting
shim.
Valve clearance (Cold):
Intake 0.15±0.25 mm (0.006±0.010 in.)
Exhaust 0.25±0.35 mm (0.010±0.014 in.)
(b) Turn the crankshaft one revolution (360 °), and align the
mark as above. (See procedure step in 19 (a))
(c) Check only the valves indicated as shown. Measure the
valve clearance.
(See procedure in step (a))
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(b) Determine the replacement adjusting shim sizefollowing Formula or Charts:
w Using a micrometer, measure the thickness of the
removed shim.
w Calculate the thickness of a new shim so the valve
clearance comes within specified value.
T
Thickness of used shim
A
Measured valve clearance
N
Thickness of new shim
Intake N = T + (A±0.20 mm (0.008 in.))
Exhaust N = T + (A±0.30 mm (0.012 in.))
w Select a new shim with a thickness as close as
possible to the calculated values.
HINT: Shims are available in thirty±three sizes in increments
of 0.025 mm (0.0010 in.), from 2.50 mm (0.0984 in.) to 3.30
mm (0.1299 in.).
(c) Install a new adjusting shim. w Place a new adjusting shim on the valve lifter.
w Press down the valve lifter with SST (A), and
remove SST (B).
SST 09248±55011
(d) Recheck the valve clearance.
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ENGINE MECHANICAL Engine Tune±UpEM±19
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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
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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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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 operating tempera-
ture.
2. DISCONNECT DISTRIBUTOR CONNECTOR
3. DISCONNECT HIGH±TENSION CORDS FROM SPARK PLUGS (See steps 2 to 8 on pages EM±10 and 11)
4. DISCONNECT INJECTOR CONNECTORS
5. REMOVE SPARK PLUGS (See page IG±8)
6. CHECK CYLINDER COMPRESSION (a) Insert a compression tester into the spark plug hole.
(b) Fully open the throttle.
(c) While cranking the engine, measure the compressionpressure.
HINT: Always use a fully charged battery to obtain engine rev-
olution of 250 rpm or more.
(d) Repeat steps (a) through (c) for each cylinder.
NOTICE: This measurement must be done in as short
time as possible.
Compression:
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
(e) If the cylinder compression in one or more cylinders islow, pour a small amount of engine oil into the cylinder
through the spark plug hole and repeat steps (a) through
(c) for the cylinder with low compression.
w If adding oil helps the compression, the piston rings
and/or cylinder bore are probably worn or
damaged.
w If pressure stays low, a valve may be sticking or
seating improper, or there may be leakage past the
gasket.
7. REINSTALL SPARK PLUGS (See page IG±9)
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
8. RECONNECT INJECTOR CONNECTORS
9. RECONNECT HIGH±TENSION CORDS TO SPARK
PLUGS (See steps 14 to 20 on pages EM±17 to 19)
10. RECONNECT DISTRIBUTOR CONNECTOR
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ENGINE MECHANICAL Compression Check
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