A compression test tests the condition of your engine valves, valve seats, and piston rings in order to see whether they're wearing down evenly or not. This helps you decide which pistons to fix or if there's some adjustment needed on your vehicle itself.
The compression tester is the tool that's used to do compression tests. It's usually for high-performance engines in a racecar or an ATV. This tester can also be used to diagnose problems with the engine as well as measuring and improving your motor's overall performance when push comes to shove.
How to Use a Compression Tester like a Pro
- What It Tests: The tester tests the condition of the valves, valve seats, and piston rings of your engine. It specifically tests where they're wearing down evenly or in a skewed fashion. An engine that's optimally working should have over 100-PSI compression for every cylinder. There should also be no more than 10 percent variation between the highest and lowest ratings.
- What to Initially Expect: It takes about 20 minutes to do an engine compression test. Let your engine run for a few minutes to warm it up to normal running temperature if you haven't used it. If it's hot instead, let it cool down for a few minutes. Afterwards, switch your engine off, remove the fuel injection fuses and fuel pump, and start the test itself.
- Disconnections and Removals: Disconnect the electrical connection of your ignition coil pack. Disconnect the main wire to the coil and the spark plug wires then remove the spark plugs. Disconnect all wires for the spark plug and be careful not to break their ceramic insulators. Thread the adapter or the threaded end of the compression gauge into the spark plug hole of the first cylinder.
- Start Your Engine Then Turn It Off: Start the engine by yourself or by assistant. Have the throttle depressed and crank the engine for 4 revolutions. If there's no stable reading, have it cranked up to 10 revolutions for all 4 cylinders instead. As the engine is cranked continuously, the pressure gauge needle should go up. Once it gets maximum reading, turn off your engine. Mark by pen and paper or chalk the pressure reading for each cylinder.
- Reading Evaluation: The readings will tend to have a 100 PIS median and vary from 175 to 250 PSI. The higher the reading the healthier your engine. Check the manual for the ideal reading on your vehicle. If the cylinder is below 100 PSI, put a teaspoon of motor oil into the plug hole the redo the test. If the reading jumps then you have worn-out piston rings. If the reading remains under 100 PSI, your valves might have issues. Do the reading even if your engine can't start. Your mechanic can use that low reading as reference.