Compression is one of the main indicators of the technical condition of a diesel engine. Compression testing is carried out at service stations using special devices - compressometers and compressographs.
Compression is the pressure that is created in the engine cylinder while it is being rotated by the starter motor, when the fuel delivery system has not yet come into operation. Compression is one of the most important indicators of engine health. Compression ratings for various engines under normal atmospheric conditions are 28-40 atmospheres.
Checking the compression of a diesel engine involves diagnostics of the cylinder-piston group, which is carried out with a special device - a compression meter or a compressor. The device includes a shut-off valve that prevents pressure release when cranking the crankshaft.
The difference between the two devices is the different way of displaying information. The dial of the dial gauge serves for these purposes in the compressometer, and the compressor allows you to display the data on a computer monitor or print a report on the test results on paper.
Compression check procedure
1. Disconnect the high pressure pump fuel shut off valve connectors.
2. Disconnect the high pressure pump dispenser.
3. Remove one of the glow plugs.
4. Connect a compressor or a compressor to the glow plug flange.
5. Measure the compression with the starter turned on. The measurement is considered complete when the compression gauge readings stop increasing.
6. Repeat the measurement, placing the device in the place of the next candle. Record the results of each test.
7. Reinstall the spark plugs.
8. Reconnect the fuel cutoff valve connectors and turn on the high pressure pump dispenser.
Test conditions
The nominal compression value and the value of the limit tolerance can be found in the operating documentation for the car.
Compression testing should be performed at a crankshaft speed of 200-250 rpm. The condition of the air filters is also a prerequisite for the accuracy of the measured readings. A clogged filter may distort the compression reading.
Compression is measured under those temperature conditions in which the actual engine start usually takes place. There is a direct relationship between ambient temperature and the minimum compression at which the engine can start. This performance for a specific engine can be obtained from a series of tests carried out in a workshop environment.
