The check is carried out with the engine warmed up to operating temperature.
Gasoline engines
1. Four-cylinder engine. Disconnect the ignition coil output stage connector.
2. Disconnect the multi-pin plug from the fuel injection unit (66 kW motor) or the power plug for all four valve injectors (85 kW motor).
3. Five-cylinder engine. Disconnect the ignition coil output stage connector.
4. Remove the #17 fuse from the fuse block.
5. Six-cylinder engine. Disconnect both plugs of the output stage of the ignition coils.
6. Disconnect the plugs of all six valve injectors.
7. Disconnect holders of wires of a high tension of spark plugs of third and fourth cylinders.
8. All engines. Remove spark plugs.
9. Insert the rubber cone of the compression gauge into the #1 cylinder spark plug hole, or screw the adapter tip into the spark plug hole. The sequence of the compression test does not matter. It is only recommended to record the number of the checked cylinder (see illustration).
10. Apply the handbrake.
11. Set the transmission to neutral. For vehicles with automatic transmission, set the gearshift lever to position «R».
12. Ask the assistant to rotate the engine with a starter. The accelerator pedal should be pressed to the stop in order to better fill the cylinders.
13. Record the reading as soon as the pressure increase in the cylinder stops.
14. Proceed to measurement of a compression on the following cylinder.
Diesel engines
15. Disconnect the fuel cut-off valve power wire on the injection pump.
16. TD engines. Disconnect the fuel lines from the injectors and place them on a clean rag.
17. Turn out all valve nozzles.
18. Remove the heat shield pads from the injector holes.
19. TD1 engines. Remove the tips from the glow plugs and unscrew the candles themselves.
20. All engines. Screw the tip of the adapter into the hole for the injector or glow plug of cylinder No. 1. When checking compression on a TD engine, place the old heat shield under the tip (see illustration).
21. Set the transmission to neutral.
22. Start a starter and wait for the pressure increase which is noted by a kompressometrom to stop.
23. Write down the received value.
24. Start measuring compression on the next cylinder.
After checking the glow plugs for a TD1 engine, screw in with a torque of 15 Nm, and for TD engines, install new heat-shielding gaskets under the valve injectors. Tighten the valve injectors with a torque of 70 Nm, and the nuts of the fuel lines on the injectors with a torque of 25 Nm.
Equally low compression, which does not go beyond the acceptable minimum values, is not a cause for concern. Lower values may be the result of tolerances specific to each type of compression meter. The cause for alarm is the increased pressure difference in adjacent cylinders. For gasoline engines, it should not go beyond 2-3 bar. The reason for the appearance of large values \u200b\u200bmay be:
- wear of pistons and piston gauges,
- jamming of piston rings with deposits,
- deformation of the cylinder as a result of piston jamming,
- accumulated deposits on the valve stems,
- burnt and leaking valves. In most cases, it is leaky valves that cause low compression and a drop in effective engine power. This defect can only be eliminated by rebuilding the cylinder head.
To determine the cause of the compression drop in gasoline engines, use the following technique. A few drops of engine oil are instilled into the spark plug hole with an oiler and the compression is measured again. If the readings are still poor, then the reason for this is valve leaks. If the pressure has increased, then the reason for its decrease is the piston rings or even the cylinders themselves. The dripped oil created an airtight film between the pistons and cylinder walls for some time, thus preventing the gases from escaping.
More accurate information about the reasons for the drop in compression pressure can be obtained by performing a compression test with compressed air. This check is performed by many workshops. During its implementation, compressed air is supplied to the combustion chamber through the hole for the spark plug. The pressure drop in the combustion chamber is recorded with a compression gauge, and the place of air leakage can be determined by ear.
The release of compressed air from the exhaust pipe, accompanied by a hiss, indicates that the exhaust valve is leaking. If compressed air comes out of the air filter, then this is evidence of a leak in the intake valve. If the cylinder head gasket is defective or the head is cracked, compressed air escapes through a hole in a nearby spark plug or through an open expansion tank with coolant. When the working walls of the cylinder, piston guides or piston rings are worn, compressed air enters the crankcase and exits through the open oil filler pipe or through the guide tube of the engine oil level indicator rod.
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