Monday, February 19, 2024

How is the compression pressure measured in the engine?

Reading time 4 Min.

How is the compression pressure measured in the engine?

In order to be able to measure the compression pressure in an internal combustion engine, the Spark plugs or injectors through a corresponding Measuring device be replaced. Appropriate adapters for the compression pressure recorder for a wide variety of engines are available here. The right connection piece can be determined in a database for the respective motor. As a rule, compression pressure gauges are used according to A distinction is made between gasoline and diesel engines.

Perform compression pressure test

Has the right adapter been found for the respective engine and that Compression pressure gauge attached, the engine is cranked with the starter to starter speed. The cylinders are now successively measured. In order to avoid intake throttling, must be with gasoline engines fully open throttle be measured. The professional measuring device for measuring compression pressure is usually a writing device. This then writes the result on a cardboard card. During the measurement, the cardboard card is pulled out a little for each cylinder. This means that several measurements per card are possible.

How is the compression pressure measured in the engine?

However, there are of course other measuring devices as well. If you have a measuring device that does not output a written record, a valve is usually built into the display to maintain the maximum pressure. In addition, these devices have a button to be able to release the pressure for the subsequent measurement. There is also a pressure gauge available as a further variant Drag pointer. This must be reset by hand before each further measurement.

How is the compression pressure measured in the engine?

In order to be able to evaluate a compression pressure measurement, one must first take a look at the common pressures of the engines. Modern engines are in pressure ranges of 11 to 15 bar for new and run-in petrol engines. Diesel engines are usually at a pressure value of 30 to 55 bar. Pre-chamber or swirl chamber diesel engines clearly have higher compression values as direct injection engines. Are the values below 8 bar in the case of a gasoline engine or below 20 bar in the case of a diesel, this is one in a modern engine Defect due to wear to go out.
Older engines, such as a VW boxer engine, have lower default and limit values. There are also special designs that have different values. Workshop manuals provide the expected pressure readings according to engine type. As the Rule of thumb one should remember: 10-15% less Compression as specified by the manufacturer is critical!

What to do if the measurement result is too low?

How is the compression pressure measured in the engine?

Should the case arise that the nominal value of the measurement is in a cylinder from unterschrit will, should be the measurement repeated to get to the bottom of the cause. Before the second measurement, however, is now some engine oil given into the combustion chamber. This has an influence on the sealing of the piston by the piston rings to the cylinder. On when measuring again higher reading indicates wear in the field of Cylinders, pistons and piston rings out.

A consistently bad measurement result rather indicates a wear-related error Cylinder head, head gasket or valve seat down. In the case of compressors or pumps, the measurement is, by the way anders carried out. A so-called pressure loss measurement is used here instead of a compression pressure measurement. For this purpose, a predefined pressure is built up when the machine is at a standstill. After switching off the pressure supply, the time for the pressure drop to the reference pressures is measured. There is even more information in our article "The pressure loss test - an engine diagnosis with air?".

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How is the compression pressure measured in the engine?

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About Thomas Wachsmuth

Thomas Wachsmuth - He has been an integral part of since 2013. His passion for cars is so intense that he invests every available penny in them. While he dreams of a BMW E31 850CSI and a Hennessey 6x6 Ford F-150, he currently drives a rather inconspicuous BMW 540i (G31/LCI). His collection of books, magazines and brochures on the subject of car tuning has now reached such proportions that he himself has become a walking reference work for the tuning scene.  More about Thomas

a comment

  1. Come may su un motore con un rapporto di compressione pari a 8 (ad esempio) nella misurazione della pressione massima di compressione (con manometro, farfalle aperte, a velocità di mot, avviamento) non si rileva 8 bar, ma un valore più alto?

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