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Compression Test

Last Updated - 01/01/02

About this How-To:

Before doing any serious modifications to a vehicle, its always best to make sure that the engine is running in good condition in the first place. A compression test will show you if the engine is good condition or could show bad rings, head gasket, valve seats or other problems that would cause lack of power.

Tools Needed:

Socket Wrench
Sparkplug Socket
Long Extension
Compression Gauge (Available at any parts store for about 20 bucks)

Parts Needed:

N/A

Notes:

This is pretty much the same on any car. Although the pressure specs may vary depending on the type of engine, the most imortant thing your looking for is that all cylinders are consistent (+ or - 10-20psi).

Start off by removing the plug wires and plugs. (Note which wires go where, some aftermarket wires may have one or two that are the same length and you don't want to switch them around) Also you may notice that I have the valve cover bolts removed in this pic. that is only because I had just done a valve adjustment.
Next, remove the 15A FI (Fuel Injector) fuse so that you don't have fuel spraying into the cylinders. It should be located in the same place as in the picture on most Hondas.
Now take a little bit of motor oil and dab some of it on the threads of the compression gauge. Then screw the gauge into the first cylinder hand tight. Crank the engine at least 5-10 times making sure that you keep the gas pedal to the floor. Now check the gauge.
In the case of the b18c you should have around 270 Psi as the normal, 140 Psi as the minimum with a maximum variation of 28 Psi between cylinders. As you can see the first cylinder is at about 260 Psi which is on the high side of the scale (which is good.) Let the pressure out by pushing the release on the side of the tester. Now repeat these steps for the remaining cylinders.
As you can see, the remaining cylinders in this b18c are at 250 Psi which shows that the compression is good between all four cylinders. It is not uncommon to have three cylinders have about the same compression and the fourth to be a little higher or lower. As long as its within spec your ok. Now go ahead and replace the plugs and wires along with the fuel injector fuse. If you have found that there are any cylinders beyond the specs listed (Or the specs for the particular engine that you are working on) repeat the procedure on that cylinder and if you get the same readings, take the vehicle to a qualified technician for further testing.