How to Check the Cylinders on a Car

Automobile internal combustion engines rely on the pressures developed within the individual cylinders for smooth, powerful performance. When one or more of the cylinders operate at a lower pressure level than the others, the engine runs rough, power is lost and fuel economy diminishes. As part of a complete and comprehensive tune-up, the cylinders should have a compression test performed that will reveal any pressure inconsistencies that may exist. The do-it-yourself car owner can perform a cylinder check of the car's engine with a compression tester and a few tools. Time involved will vary depending on the make and model of car.

• 1

  Run the car's engine until it has fully warmed up to perform an accurate check. The integrity of the test relies on all internal engine components and the oil being warm.

• 2

  Remove the engine fuel pump fuse with the fuse extractor if the car is equipped with an electric pump. Check the car's service manual for the location of this fuse.

• 3

  Remove the ignition coil wire with the plug wire pliers. Grip the wire as near to its base as possible and pull it straight out of its recess. Check the maintenance manual for your particular car to locate the coil wire.

• 4

  Remove one of the spark plugs using the appropriate size insulated deep-well socket connected to the ratchet wrench. Make sure the socket is seated fully on the plug. Turn it in a counterclockwise direction to remove.

• 5

  Insert the tapered rubber end of the compression tester into the cylinder spark plug hole. Hold the tester firmly in the hole to prevent air leakage.

• 6

  Instruct the helper to turn the engine over while holding the throttle pedal in the full open position. This ensures the engine takes in an adequate amount of air for the test. Five to ten turns of the engine will suffice for an accurate pressure reading.

• 7

  Record the compression tester reading for each of the engines' cylinders. If there is a variance between any of the cylinders of greater than 10 percent, a professional diagnostic test must be performed to diagnose the problem fully. If all cylinder readings are within 10 percent of each other, no further testing is required and compression is considered optimal.

• 8

  Replace the last removed spark plug, ignition coil wire and the fuel pump fuse using the appropriate tools.