ENGINE COMPRESSION TEST: HOW IS IT DONE?

1. WARM YOUR ENGINE UNTIL IT REACH THE NORMAL OPERATION TEMPERATURE

Engine compression test is done with engine is at normal operating temperature. Let it idle for 20 mins. then turn it off. Do not let your engine becomes too hot because it will be dangerous for the spark plugs to be removed when it is too hot that it might break and cause more problem to your engine.

2. IF YOUR FUEL PUMP IS ELECTRONICALLY OPERATED - DISABLE IT

Turn off or disable electronic fuel pump to avoid the fuel from being injected into the cylinders

3. DISCONNECT THE HIGH TENSION WIRES AND REMOVE ALL SPARK PLUGS

Disconnect all high tension wires and remove all the spark plugs(remember do not remove spark plugs if the engine is too hot). Disconnect the high tension wire from the ignition coil to cut the secondary circuit.

4. CONNECT THE COMPRESSION TESTER ON EACH CYLINDER - ONE AT A TIME

Connect the compression tester to spark plug hole at each cylinder. DO NOT USE WRENCH OR ANY TOOL WHILE TIGHTENING THE COMPRESSION TESTER. Do it with your bare hands only.

5. ASK A FRIEND TO CRANK THE ENGINE

A friend or an assistant will crank the engine several times while pressing the accelerator pedal fully while you are holding the compression tester and check the needle's movement. Crank the engine several times until the needle stops rising then record the final reading. This test should be done on all cylinders.

6. CLOSELY MONITOR THE NEEDLE'S MOVEMENT WHILE YOUR ASSISTANT IS CRANKING THE ENGINE

In every engine crank the needle in the tester should respond and rise. If the needle is not responding to the cranking of the engine then suddenly rises or have a reading then you might have a sticky valve. Servicing the valve will correct the problem.

7. COMPARE THE READING OF EACH CYLINDERS

Each cylinders compression should be close to each other. If one or two cylinders are 14 psi lower than the other it might be the piston rings or the cylinder linings are at fault. Do the compression test again but this time squirt a small amount of oil to the cylinder and let it still for a couple of minutes then do the compression test. If the compression changes; then the piston rings or cylinder are at fault. If not. the valves are at fault.

The video below is an example of actual compression testing

HOW TO: ENGINE COMPRESSION TEST