How to Use Compression Tester

The internal combustion engine has four strokes: intake, compression, combustion and exhaust. Several components must work in harmony to create the perfect environment to keep the engine running.

Moreover, each stage is integral to the process – if something is not right, your automobile will alert you. Compression problems do not occur very often, but when they do, you are already looking at significant repairs. Using a compression test to diagnose them early can save you a lot of time and hassle in the long run.


The cause of low compression can be anything from worn piston rings to stuck valves to a blown head gasket to a broken timing belt. And more! There could be misfiring, decreased power when climbing hills, or your car might not start.

When it comes to most of these scenarios, compression problems shouldn’t be the first thing you consider. However, if you’ve ruled out other causes, or if the engine begins cranking excessively quickly when you turn it on, get a compression tester.


The engine should be cold when you begin. Fuel pump relay and main ignition coil wires should be disconnected. The procedure will be prevented from being hampered by fuel and spark.

Next, make a note of the order and location of spark plug wires prior to removing them so that you can replace them in the same order later. Be careful not to damage the ends of the spark plugs when you remove them. Keep them in order, as well, and inspect each one for clues that something is wrong with the combustion chamber.


Starting with cylinder 1 (consult your owner’s manual for the cylinder ordering numbers), thread the compression adapter into the spark plug hole. The majority of compression testers consist of two or more pieces that are threaded or snapped together from the closest parts toward the engine out – all by hand.

After that, have a friend crank the engine for five seconds or so while you observe the gauge. On most vehicles, you want to find the highest number reached, which is typically between 125 and 160 psi. Make a note of this number and disconnect the tester, then repeat for each cylinder.

By comparing one cylinder’s compression with the others, you’ve narrowed down the compression issue to that cylinder. In the event that you have low measurements across the board, it is likely a timing chain issue or a mechanical failure.

In any case, head on over to your localĀ NAPA AutoCare, we recommend a comprehensive diagnosis because low compression is no joke, and continuing to drive (if you can) will cause a lot of damage. Take care of this problem as soon as possible before things get worse.

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