Checking Compression Pressure

Before checking the engine compression, check the engine oil level. Also check that the starter motor and battery are all in normal operating condition.
Start the engine and wait until the engine coolant temperature reaches 80-95°C (176~205°F).
Stop the engine and disconnect the spark plug cables.
Remove the spark plugs.
Crank the engine to remove any foreign material in the cylinders.
Insert the compression gauge into the spark plug hole.
Depress the accelerator pedal to open the throttle fully.
Crank the engine and read the gauge.
Standard value: 1,200 kpa (12.2 kg/cm² , 170 psi)

Limit: 1,050 kpa (10.7 kg/cm² , 149 psi)

Fig 1: Checking Engine Compression With Compression Gauge
Courtesy of HYUNDAI MOTOR CO.
Repeat steps 6 to 8 for all cylinders, making sure that the pressure difference for each of the cylinders is within the specified limit.
Limit:

Max. 100 kpa (1.0 kg/cm² , 14 psi) between cylinders
If a cylinder's compression or pressure differential is outside the specification, add a small amount of oil through the spark plug hole, and repeat steps 6 to 9.
1. If the addition of oil causes the compression to rise, it is possible that the piston ring is worn.
2. If the compression remains the same, valve seizure, poor valve seating or a compression leak in the cylinder head gasket are all possible causes.
  Tightening torque
  
  Spark plug: 20 ~ 30 Nm (200 ~ 300 kg.cm, 14 ~ 22 lb. ft)