Checking Compression Pressure

Before checking compression, check the engine oil level and that the starter motor and battery are all in normal operating condition.
Start the engine and wait until engine coolant temperature has risen to 80-95°C
Stop the engine and disconnect the spark plug cables.
Remove the spark plugs.
Turn over the engine to remove any foreign objects in the cylinders.
Attach the compression gauge to the spark plug hole.
Depress the accelerator pedal to fully open the throttle valve.
Turn over the engine and read the gauge.
Standard value:

1,275 kPa (13.0 kg / cm² , 185 psi).

Limit: 1,128 kPa (11.5 kg / cm² , 164 psi).

Fig 1: Checking Compression Pressure
Courtesy of KIA MOTORS AMERICA, INC.
Repeat steps 6 - 8 on all cylinders, making sure ensuring that the pressure difference for each of the cylinders is within the specified limit.
Limit:

Max 100 kPa (1.0 kg/cm² , 14 psi) for all cylinders.
If a cylinder's compression or pressure difference is below the specification, add a small amount of oil through the spark plug hole and repeat steps 6 - 9 .
1. If the addition of oil causes the compression to rise, it is possible that there is wear between the piston ring and cylinder wall.
2. If the compression doesn't rise, valve seizure, poor valve seating or a compression leak from the cylinder head gasket are all possible causes.
Tightening torque:

Spark plug:

20-30 N.m

(200-300 kg. cm, 14.75-22.13 lb. ft)