Compression test
Attention! The check is carried out using a special compression tester for diesel engines, designed for high pressure. The check is made with the engine warm (oil temperature around 30°C).
1. If the engine efficiency decreases, as well as in the event of misfiring, the compression pressure in the cylinders should be measured, the analysis of the results of which will determine 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 an adapter, is connected to the holes for installing fuel injection nozzles or glow plugs. The meter is quite expensive and it does not always make sense to purchase it for personal use. If necessary, you can contact the services of car service specialists.
3. Unless special instructions are attached to the compression gauge, 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, unscrew all four nozzles (or all four glow plugs). The nozzles should be removed complete with flame arrester washers to prevent the latter from blowing out.
- c) The solenoid shut-off valve must be disconnected to prevent accidental engine starting or fuel ejection.
- d) Be sure to disconnect the main engine cable multi-pin connector located behind the left front suspension strut upper mount.
4. Due to the fact that the air path of the diesel engine is not equipped with a throttle valve, the need to hold the gas pedal depressed is automatically eliminated.
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. In case of doubt, please consult a car service specialist.
6. The reason for the reduction in compression pressure on a diesel engine is not as easy to establish as on a gasoline one. The method with adding oil to the cylinders in this case does not work due to the risk of oil settling on the walls of the vortex chambers, instead of lowering it to the piston rings. Below are the main points of interpretation of the test results.
7. The results of measuring the pressure in all cylinders should be very close to each other. A spread of 5 bar indicates the presence of internal problems in the engine. In a healthy engine, pressure should build up very quickly. A low reading on the first stroke, followed by a gradual increase in subsequent strokes, indicates worn piston rings. If the pressure does not rise at all, you should check the tightness of the closing 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 with a high degree of probability indicates a violation of the integrity of the head gasket in the area of the jumper between these cylinders. The presence of traces of coolant in the crankcase will confirm this assumption.
9. If the compression value is noticeably higher than the norm, the cylinders should be decarbonized by removing carbon deposits on 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 compression pressure, but its results allow you to get more complete information about the condition of the engine due to the ability to quickly determine the source of the leak (piston rings, valves, gasket, etc.).
2. Due to the need to use special equipment, this check should be entrusted to car service specialists.