Compression Check - Toyota 4-Runner 1985 Repair Manual

ENGINE MECHANICAL - Compression Check
EM-11
COMPRESSION CHECK
NOTE: If there is lack of power, excessive oil consump-
tion or poor fuel mileage, measure the cylinder compres-
sion pressure.
1. WARM UP ENGINE
2. REMOVE FOUR SPARK PLUGS
3. DISCONNECT HIGH TENSION WIRE FROM IGNITION COIL
4. MEASURE CYLINDER COMPRESSION PRESSURE
(a) Insert a compression gauge into the spark plug hole.
(b) Fully open the throttle.
(c) While cranking the engine with the starter motor,
measure the compression pressure.
CAUTION: This test must be done for as short a time as
possible to avoid overheating of the catalytic converter.
NOTE: A fully changed battery must be used to obtain
at least 250 rpm.
(d) Repeat steps (a) through (c) for each cylinder.
Compression pressure: 12 kg/cm2 (171 psi, 1,177 kPa)
Minimum pressure: 10 kg/cm2 (142 psi, 981 kPa)
Difference between each cylinder:
Less than 1.0 kg/cm2 (14 psi,
98 kPa)
(e)
If 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 low compression cylinder.
• If adding oil helps the compression, chances are that
the piston rings and/or cylinder bore are worn or
damaged.
• If pressure stays low, a valve may be sticking or
seating improperly, or there may be leakage past
the gasket.