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Compression problems in the engine: what is the cause and how to detect it?

The internal combustion engine receives this name because it generates mechanical energy from a fuel and oxygen combustion process carried out inside a chamber designed for this purpose.

This chamber is the cylinder, inside which a two or four stroke cycle, depending on the type of engine we are talking about.

In the case of automotive engines, the engines usually have at least three or four cylinders and all of them must work in a very similar way and under very specific conditions in order to develop their full potential.

What is compression ratio

For these conditions to be met, the compression ratio, as it directly influences the thermal performance of the engine or, in other words, the engine’s ability to take advantage of the energy generated in combustion.

The compression ratio is the difference in volume between the air / fuel mixture (only air in diesel engines, since diesel is injected later) when it is compressed and when it has already been detonated inside the cylinder.

Poor compression usually occurs because the cylinder seal deteriorates or loses

We can also interpret it as the difference in volume between the two extreme positions of the piston inside the cylinder: when it is in its PMI (Lower Dead Center) and when it amounts to your TDC (Top Dead Center).

If the compression ratio of a cylinder drops, then an abnormality will occur resulting in problems and lower performance of that engine.

What causes compression problems

Poor compression, which is actually a drop in compression or low compression in the cylinder, usually occurs because its sealing deteriorates or loses as a result of some leakage or defect. The most common are:

Synchronization: If the engine timing is not correct, the valves do not seat correctly or do so at the wrong time. Similarly, if one of the valves is damaged, leakage and compression drop will occur.Butt: If the gasket is damaged or improperly installed or there are cracks in the cylinder head, it will cause leakage and a compression drop. The same can be said for the engine block.Spark plug– If it is misplaced, loose, or the thread is defective, it will leak.Piston rings and / or cylindersThese elements guarantee the seal, but if they are loose or worn they will create gaps or leaks and will not be able to fulfill their function.Oil: generates low compression if it is of poor quality as a result of degradation or an incorrect specification for that type of engine.Air filter or catalyst: clogging these elements can also cause poor compression.

How to know if there is a compression problem

When one of the engine elements fails, they develop symptom that allow us to determine the cause. The same is true for compression problems, which often cause the following problems:

Smoke present in the exhaust due to poor combustion. powersince the usual power cannot be generated. consumption of fuel by forcing the engine to work harder to achieve the same performance.Slow motion unstable as there is no uniformity of work in the motor. start or unwanted engine shutdown Water and coolant consumption Increased amount of emissions pollutants as a result of poor combustion.

As a general rule, a difference of more than 10% between the compression of the cylinders indicates a problem that needs to be fixed.

So we can measure the compression of the engine.

If low compression is present in all cylinders, the problem may be in what is called ‘cylinder wash’, which occurs when the oil layer that covers the cylinder walls, piston and rings is lost as a result of an excess of fuel, since the seal of the whole is canceled.

If, on the other hand, one of the cylinders offers a very low or no compression measure, it is most likely that the piston or connecting rod that cylinder is broken or a valve is stuck or leaking. It can also occur when the camshaft is worn excessively, preventing proper valve operation.

Finally, if what happens is that the compression is too high in one or more cylinders, what can happen is that too much soot has been deposited in the engine. Something that can only be corrected by carrying out a chemical process decarbonization on the engine or by removing the cylinder head from the engine to clean the top of the piston head and the valve opening area.

How to measure compression

Although it is always advisable to go to a specialized workshop, we can perform a compression measurement if we have the appropriate tools, mainly a compression gauge and one spark plug wrench:

Disconnect the ignition system Remove the spark plug wires as well as the spark plugs themselves Connect the pressure gauge to one of the spark plug holes Throttle fully to fully open the throttle handle Turn the ignition key to the start position for at least 5 seconds Check the values ​​indicated by the pressure gauge Repeat the operation on all cylinders Compare the values ​​with those recommended by the manufacturer.

We must take into account that modern vehicles will generate a Error code caused by the disconnection of the ignition, something that will pose problems in the ITV. there are tools or code readers to eliminate them.

Do you want to know why each engine needs a certain compression ratio and what is the connection between it and the octane rating, or why it is higher in diesel engines? Do not miss this article.