Content

• To step
• Tips
• Necessities

A compression measurement is normally taken to test the engine of racing cars and tuned cars. The measurement can be used to diagnose problems in the engine or to measure and improve engine performance. If you want to learn how to perform a compression measurement, it is useful if you have some basic knowledge about car parts and maintenance.

To step

1. Bring the engine block to operating temperature. This can be done in the following ways.
   • If you have not just driven your car, the engine is probably cold. Start your engine as normal and let the engine run for a few minutes. This way you bring the block to normal operating temperature; but watch that the engine does not overheat by idling for too long. Normally, 20 minutes of running is enough.
   • If you have just ridden the engine, turn the engine off and let it cool down. If the block is hot, let the engine cool for about an hour before taking the compression measurement.
   • If you cannot start the car, you can still carry out the measurement. In that case, you cannot accurately measure engine operation, but you can still determine if there is a problem with the internal compression if you get a low reading.
2. Turn off the engine completely before starting the measurement.
3. Remove the fuel pump relay. By removing the voltage from the fuel pump, you ensure that no fuel is injected into the cylinders.
4. Disconnect the ignition coil electrical connection. In this way, the ignition no longer works, because the ignition coil cannot generate and distribute spark plug spark.
5. Remove the spark plugs and disconnect the wires from each spark plug. Handle the spark plugs carefully, as the ceramic insulation of a spark plug can be damaged or broken.
6. Insert the compression gauge into the spark plug hole of the first cylinder (this is the hole closest to the timing belt). Do not use any extra tools to secure the compression gauge, just use your hand to apply pressure.
7. Ask someone to start the engine. The pointer on the meter will go up, when the pointer stops rising, your assistant can turn off the engine. What the meter now indicates is the maximum compression value of the first cylinder.
8. Repeat the compression measurement for the remaining cylinders until you have measured all cylinders in your car.

Tips

• The results of a compression measurement typically fall between 175 and 250 PSI (Pounds per Square Inch). A higher reading normally indicates better engine performance. But it is a good idea to check what the ideal measurement should be for your car.

Necessities

• Compression gauge