Poor engine traction, sluggish acceleration, black exhaust - all these are, perhaps, links in the same chain - poor compression. To be sure of this for sure, it is necessary to measure the pressure in the cylinders.
Compression is the maximum pressure in the engine cylinder when the piston approaches top dead center. To measure compression, you need to get a special device - a compression meter: this is a pressure gauge attached to a rubber tube or metal tube with a fitting at the end. To take measurements, you will need an assistant to turn the crankshaft with the starter. Compression can be measured if the valves on the engine are correctly adjusted.
Compression measurement on VAZ2109
Start the engine and warm it up to operating temperature. Stop the engine, remove the spark plugs. Shut off the fuel supply; to do this, you can disconnect the fuel hose and pinch it so that the gasoline does not flow out. Throttle, air damper must be fully open. Now firmly insert the compression gauge fitting (or screw, depending on the model of the device) into the spark plug socket.
Ask an assistant to crank the crankshaft with the starter. Observe the readings of the compression gauge and record its readings separately for each cylinder. The minimum allowable amount of compression in the VAZ2109 cylinders is 10 kg / sq. see These values should not differ by more than 1 kg / cm. sq.
If the compression in one of the cylinders is less than the specified number, then there is cause for concern; the reason may lie in the wear of the piston rings, insufficient tightness of the cylinder head gasket (cylinder head), poorly ground valves, and wear of the cylinder walls. Almost all of these problems are solved through engine overhauls.
Determining the causes of poor compression
If, during the tests, a hiss is heard from the spark plug socket of the adjacent cylinder, then, most likely, the cylinder head gasket is damaged: it is not so difficult to replace it. It is more difficult if the hiss of air is heard from the exhaust pipe or in the area of the manifold, this means that one of the valves (or several) does not fit tightly to its seat.
There is another method for determining the cause of loss of compression in a problem cylinder. To use it, pour 25-30 g of engine oil through the plug socket and measure the compression again. Compare the readings: if they are the same, then the cause of poor pressure is a loose valve or a breakdown of the cylinder head gasket. To determine if the latter is damaged, just look under the radiator cap - in this case, you will see air bubbles. If the compression has increased, then the reason should be sought in worn out (broken) rings.
