Lexus SC300 / Lexus SC400. Manual - part 426

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. 

REMOVE NO.3 TIMING BELT COVERS
(See steps 1, 5 to 10 and 14 on pages 

EM–11

 to 13)

3. 

DISCONNECT COLD START INJECTOR CONNECTOR

4. DISCONNECT RH CAM POSITION SENSOR

CONNECTOR
(a)  Disconnect the connector from the ignition coil bracket.
(b)  Disconnect the sensor connector.

5. DISCONNECT LH CAM POSITION SENSOR

CONNECTOR

6. REMOVE 

SPARK 

PLUGS

(a)  Disconnect the eight high–tension cords from the spark

plugs.

Disconnect the high–tension cords at rubber boot. Do
not pull on the cords.

NOTICE: Pulling on or bending the cords may damage
the conductor inside.

EM–30

–

ENGINE MECHANICAL

Compression Check

(b)  Using a 16 mm spark plug wrench, remove the eight

spark plugs.

7. 

CHECK CYLINDER COMPRESSION PRESSURE
(a)  Insert a compression tester into the spark plug hole.
(b)  Fully open the throttle.
(c)  While cranking the engine, measure the compression

pressure.

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 pressure:

1,226 kPa (12.5 kgf/cm, 178 psi) or more

Minimum pressure:

981 kPa (10.0 kgf/cm, 142 psi)

Difference between each cylinder:

98 kPa (1.0 kgf/cm, 14 psi) or less

(e)  If the cylinder compression in one or more cylinders is

low, 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.

•

If adding oil helps the compression the piston rings
and/or cylinder bore  are probably worn or
damaged.

•

If pressure stays low, a valve may be sticking or
seating improper, or there may be leakage past the
gasket.

8. REINSTALL 

SPARK 

PLUGS

(a)  Using a 16 mm plug wrench, install the eight spark

plugs.

Torque: 18 N

⋅

m (180 kgf

⋅

cm, 13 ft

⋅

lbf)

(b) Connect the eight high–tension cords to the spark

plugs.

(c)  Fit the high–tension cords to the cord clamps.

(See page 

IG–16

)

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ENGINE MECHANICAL

Compression Check

EM–31

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.  RECONNECT COLD START INJECTOR CONNECTOR

12.  REINSTALL NO.3 TIMING BELT COVERS

(See steps 28 to 30, 34 to 37, 40 and 41 on pages 

EM–25

to 27)

EM–32

–

ENGINE MECHANICAL

Compression Check

TIMING BELT

COMPONENTS FOR REMOVAL AND
INSTALLATION

–

ENGINE MECHANICAL

Timing Belt

EM–33