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Engine Compression Test

Abhijit Naik
One of the best methods of evaluating the performance of your vehicle, engine compression test is fairly easy. In fact, you can carry out a manual test on your car engine by yourself.
For the engine to run smoothly, it is necessary that each cylinder sports equal engine compression ratio. Irregular compression in different cylinders will eventually show in the form of adverse effects on the performance of the vehicle.
The best way to check whether poor compression is the reason for your vehicle's poor performance, is to carry out an engine compression test. It won't just help you detect the compression levels in different cylinders, but will also help in detecting various engine problems, thus helping you initiate repairs before these problems become irreversible.

Compression Test Methods

Basically, there are two compression test methods. Both have their own advantages and disadvantages. If you plan to carry out the task on your own, you should ideally choose the manual method, as it is relatively easy to execute.

Manual Testing With a Compression Gage

You will require a compression gage to test engine compression. The foremost thing you need to do is, disable the power to the ignition or fuel system. This can be done by removing the ignition coil connector or fuel pump fuse. You should check the ignition system to ensure that power is genuinely disabled.
Remove the spark plug from the first cylinder and insert the compression gage into it. Once the gage has been properly inserted, you will have to crank the engine for approximately five seconds and record the compression readings shown on the gage. Repeat the same procedure with each of the cylinders and compare the readings at the end.

Electronic Testing With an Engine Analyzer

In case of electronic testing, a computer operated analyzer is used to estimate the compression status of each cylinder. This is done by measuring minor variations in engine cranking speed. Using the engine compression, a formula is fed in the machine.
Being computer operated, it is relatively less time-consuming. You don't have to remove spark plugs and you actually get a print out of the compression test readings, thus making comparison very easy.

Engine Compression Problem

Normal compression readings are assumed to be anywhere between 125 psi and 160 psi. A difference of 5 percent within the readings of all cylinders is normally allowed. Anything less or more than the normal readings has to be subjected to further scrutiny. Low compression ratings indicate cylinder malfunctioning.
In this case, you will have to take the vehicle to a proper workshop for further check up. The problem may be anything ranging from a broken piston ring to burned exhaust valves. On the other hand, high compression ratings indicate excessive carbon buildup in the engine.
Subjecting your vehicle to engine compression testing once in a while, is a healthy practice. Whether you do it on your own or get it done from a professional, it hardly matters. If you intend to do it yourself, you can refer to engine compression charts for the particular model you own, which will be available online.
As we have said earlier, the test is of great help in determining various problems associated with vehicle engine, and if you don't remember when was the last time you went for it, now is the time.