Engine compression is one of the primary measures of power and efficiency. In a multi-cylinder engine, it is important that the power is balanced along the crankshaft. One method of measuring the balance is by testing how much each cylinder loses pressure with a tool known as a Cylinder Leak-down Tester. Rather than determining the raw amount of compression, a leak-down test can more accurately pinpoint the reason for lack of compression as well as an imbalance in cylinder pressure. Compression and efficiency depend on the perfect integration of straight cylinder walls, completely sealed piston rings and fully closed valves.
Open the hood. Start and warm up the engine. Put the vehicle in park or neutral and set the brake. Locate the distributor, it is a cylindrical shape with wires attached at the perimeter and one in the center. The plastic cap will have a mark to indicate the position of the number one cylinder. Mark this position on an easy to see component with the crayon or paint pen. Use the tags to mark each wire's position on the cylinders. Remove the distributor cap using a screwdriver from your kit. Carefully pull the wires off the spark plugs by gripping the boot.
Locate the crankshaft pulley at the front of the engine. It will be the lowest mounted pulley in the center of the engine. Use a long-handled ratchet with a socket from your kit to turn the engine until the pointer in the distributor is aimed at the number one cylinder mark you made on the engine. Use the spark plug wrench to remove all spark plugs. Keep them in order to reinstall in the same position.
Check the position of the distributor indicator. If the piston is not at top dead center the readings will be erroneous. Insert the spark plug adapter from the tester kit in the number one cylinder and connect the gauge. Use the air compressor to pump approximately 100 pounds of pressure into the cylinder or follow the manufacturer's instructions. Watch the leak-down gauge and make a note of the percentage indicated.
Turn the crankshaft bolt and move the pointer in the distributor to each subsequent cylinder in the firing order. Test each for leakage and note the gauge reading. If any cylinder shows a wide variation, make sure you have followed the firing order and the cylinder you are testing is at top dead center. Listen carefully for air leakage and try to determine its source. Take notes of the character (loud, soft, low-pitch, high-pitch) for comparison to the product manual's reference section.
