How To Perform A Compression Test: Step-By-Step Guide

Nov 25

A compression test is an important way to check the engine’s health. For the engine to run smoothly, each cylinder needs to have similar compression. A drop in compression usually indicates an air leak, which could be due to worn piston rings, damaged cylinder walls, a faulty head gasket, a cracked engine block, or leaking intake and exhaust valves.

tools you will need

compression test

The first step is to warm up your engine until it reaches operating temperature, which should take about 10 to 15 minutes.
The second step is to open the fuse box and remove the fuel pump relay. This will help you cut the fuel supply to the engine.
Next, you want to start the car and burn off the leftover fuel. You should keep your car running until the engine dies. To ensure the fuel system is fully drained, try starting the car one more time.
The next step is to remove any obstructions around the ignition coils to make it easier to remove them.
With all the obstructions out of the way, unplug the ignition coil connectors.
The sixth step is to unscrew the bolts on the ignition coils and remove all four coils. When putting everything back together make sure each coil returns to the same cylinder it came from.
The next step is to remove all spark plugs using a spark plug socket.
The eighth step is to take out your compression tester and choose the correct adapter that matches the spark plug size in your vehicle. Now, screw the adapter onto the compression tester hose.
Starting with the cylinder 1, screw the compression tester hose in by hand.
Next, have someone press down on the gas pedal and start the car at the same time. Holding down the pedal is important because it allows the engine to take in the maximum amount of air. Wait until you hear 4-5 cranks, then tell them to turn off the car. Make sure to record the final reading.
Repeat this process with all cylinders and record each psi reading.
Generally speaking, you want the PSI pressure to be similar across all cylinders. On most vehicles, the pressure difference should not be greater than 20 percent from the smallest reading to the largest, however, make sure to look into your repair manual for specifications.
Hopefully, your engine passed the test and you don’t have any major issues. Finally, just put everything back together in reverse order.