Compression check
Attention! The check is performed using a special compression tester for diesel engines, designed for high pressure. The check is performed with the engine warmed up (oil temperature about 30°C).
1. If the engine output efficiency decreases, as well as if misfires occur, the compression pressure in the cylinders should be measured, the analysis of the results of which will allow determining the general condition of the engine. Regularly checking the compression pressure will help to identify the symptoms of malfunctions in time and prevent the development of their causes.
2. A special compression tester for diesel engines, equipped with a transition nozzle, is connected to the holes for installing fuel injection nozzles or glow plugs. The measuring device is quite expensive and it does not always make sense to buy it for personal use. If necessary, you can contact the services of car service specialists.
3. If there are no special instructions attached to the compression tester, the following general rules should be followed:
- a) The engine must be warmed up to normal operating temperature, the air filter cleaned and the battery fully charged;
- b) Before starting the procedure, all four injectors must be unscrewed (or all four glow plugs). The injectors should be removed together with the flame arrester washers to avoid the latter being blown out.
- c) The solenoid shut-off valve must be disconnected to prevent accidental engine starting or fuel spillage.
- d) Remember to disconnect the engine main wiring harness multi-pin connector located behind the left front suspension strut upper support.
Text taken from this website (SKODABOOK.RU)
4. Since the air tract of a diesel engine is not equipped with a throttle valve, the need to hold the gas pedal depressed is eliminated automatically.
5. The results of the compression measurement should be compared with those given in Specifications at the beginning of this Chapter with the required parameters. If you have any doubts, consult with car service specialists.
6. The reason for the decrease in compression pressure on a diesel engine is not as easy to determine as on a gasoline engine. The method of adding oil to the cylinders does not work in this case due to the risk of oil settling on the walls of the swirl chambers instead of going down to the piston rings. Below are the main points for interpreting the test results.
7. The pressure readings in all cylinders should be very close to each other. A spread of 5 bar indicates internal engine problems. In a healthy engine, the pressure should increase very quickly. A low reading on the first stroke, followed by a gradual increase on subsequent strokes, indicates worn piston rings. If the pressure does not increase at all, you should check the tightness of the valves and the condition of the cylinder head gasket (the possibility of cracks in the body of the head itself is also not excluded).
8. Equally low pressure in two adjacent cylinders most likely indicates a breach of the integrity of the head gasket in the area of the bridge between these cylinders. The presence of traces of coolant in the crankcase will confirm this assumption.
9. If the compression value significantly exceeds the norm, decarbonization of the cylinders should be performed, removing carbon formation products from their walls.
Checking cylinders for leaks
1. The method is based on measuring the rate of pressure reduction in the cylinder after compressed air is supplied to it. The procedure is a kind of alternative to checking the compression pressure, and its results allow obtaining more complete information about the condition of the engine due to the ability to more quickly identify the source of the leak (piston rings, valves, gaskets, etc.).
2. Due to the need to use special equipment, this check should be entrusted to car service specialists.