If you suspect that a cylinder has low compression, you should use a compression meter to check it in individual cylinders. This is more difficult to do on a diesel engine, since an adapter is required that is screwed in instead of spark plugs. This identifies pistons, valves or piston rings that are not holding pressure. If the engine is still relatively new, compression should be around 32.0 Bar. The wear limit is 20.0 Bar. If the compression is below this value, you must decide whether to replace or repair the engine. It is also important whether one or all cylinders have poor compression. If, for example, the difference between individual cylinders is 5.0 atm, it may be that "bad" the valves are stuck in the cylinder and only the cylinder head needs to be repaired, that is, the valves need to be repaired. It is also possible that the piston rings are burnt in the grooves, which leads to the release of pressure along the piston into the crank mechanism. With the same loss of compression, in most cases it can be judged that the cylinders are worn out. To check compression, warm up the engine to operating temperature and remove the glow plugs. Disconnect the wire from the fuel shut-off valve. Connect the compression tester in accordance with the manufacturer's operating instructions. The assistant should get into the car and turn on the starter for about 5 seconds, while pressing the gas pedal all the way. Check the compression in all cylinders sequentially and compare with the specified value. If the compression is low in one cylinder, you can pour an appropriate preparation into the spark plug hole as first aid to temporarily restore density. Information about these products can be obtained from auto parts dealers.