Sequence of execution
1. Prepare the car for work (see "Preparing the car for maintenance and repair").
2. Warm up the engine to operating temperature and turn off the ignition.
3. Remove the fuses of the ECU and engine control system circuits (see "Fuses and relays of the engine management system").
4. Relieve the fuel pressure (see "Fuel Line - Pressure Relief").
5. Unscrew the spark plugs (see "Spark plugs - replacement").
6. Install the compression gauge into the spark plug hole of one of the engine cylinders.
7. The assistant presses the gas pedal all the way to the floor (to fully open the throttle valve) and turns on the starter for 5-10 s.
Note: Measurements must be taken with a fully charged battery, otherwise the readings will be incorrect.
8. Remember or write down the compression meter readings and reset the device.
9. Similarly, we measure the compression in the three remaining cylinders.
In a serviceable engine, the compression in the cylinders should be at least 1.0 MPa (10 bar), and the difference in compression between the cylinders should be no more than 0.1 MPa (1.0 bar).
10. If the compression is lower, then using a medical syringe or oiler, pour about 10 cm³ of motor oil into the spark plug holes of the cylinders of the engine with low compression.
11. Repeat the compression test. If the compression has increased, the rings may be stuck or the piston group may be worn out (see "Piston rings and connecting rod bearings - replacement"). Otherwise, the valves do not close tightly or the cylinder head gasket is faulty.
Recommendation. You can try to eliminate valve sticking with special preparations poured into the fuel tank or directly into the engine cylinders (see the "Instructions" for the preparation). The tightness of the valves can be checked with compressed air under a pressure of 0.2-0.3 MPa (2-3 kgf/cm³), supplied through the spark plug holes. Air must be supplied when the camshaft is in a position where both valves of the cylinder being tested are closed. If the exhaust valve is faulty, air will escape through the exhaust system, and if the intake valve is faulty, air will escape through the throttle body. If the piston group is faulty, air will escape through the oil filler neck. Air bubbles escaping through the coolant in the expansion tank indicates a faulty cylinder head gasket.