Content

• Steps
• Tips
• What do you need

Engine compression measurements are most commonly done on racing cars and other high-powered cars. This measurement is made in order to identify a malfunction of the engine or to increase its power. To learn how to measure compression, you will need basic knowledge of engine design.

Steps

1. 1 Warm up the engine to its operating temperature. This can be done as follows.
   • If you have driven your car some time ago, it is most likely cold. Start the engine and let it run for a while.After a while, the engine will reach its operating temperature, but you should be careful not to overheat the engine. Often 20 minutes is enough.
   • If you've just driven a car, allow the engine to cool slightly. If the engine is hot, wait approximately 1 hour before taking a compression measurement.
   • If you are unable to start the engine, you can still measure the compression. At the same time, you will not be able to find out how efficiently the engine works, but you will understand if the engine does not start due to too low compression.
2. 2 Stop the engine before testing.
3. 3 Remove the fuel pump relay. This will shut off the fuel system and no fuel will be supplied to the cylinders.
4. 4 Disconnect the wires from the ignition coil. This will de-energize the ignition coil and will not supply voltage to the spark plugs.
5. 5 Disconnect the spark plug wires and then remove the spark plugs. Handle spark plugs with care as you can damage the ceramic insulator and cause plug malfunction.
6. 6 Insert the compression gauge in place of the first spark plug, the one closest to the timing belt. Do not use any wrenches to tighten the appliance, hand tighten only.
7. 7 Have an assistant start the engine. The needle of the device will react and reach its maximum, as soon as it has reached its maximum, ask the assistant to stop turning the engine. This value is the compression in the first cylinder.
8. 8 Repeat measurements for all cylinders using this procedure.

Tips

• Compression readings for different engines should range from 175 to 250 PSI. More compression means more engine power, but you should check the instructions for your car's engine to find out which value is optimal.

What do you need

• Compressometer